Posted: 10/28/2013 9:32:41 AM EDT
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I'm sure it's been asked but I'm lazy today so I am not going to search.
Portable generator, which will be attached to power mains via interlock assembly. Do I still need to supply a ground for the generator by physically attaching it to the ground rod for the house? Can I drive a ground rod next to the generator and use that? Thanks. P |
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Yes, it <should> be grounded. Some appliances require it (our microwave won't run on the generator unless I ground it). Some appliances don't care. Some codes/localities REQUIRE it to be grounded. There should be a grounding point on your generator somewhere. You simply buy a small grounding rod and piece of grounding copper and leave it as dedicated, you can tie into the grounding rod for your house, etc. I have yet to ground mine. That said, ground it.
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Quoted: Yes, it <should> be grounded. Some appliances require it (our microwave won't run on the generator unless I ground it). Some appliances don't care. Some codes/localities REQUIRE it to be grounded. There should be a grounding point on your generator somewhere. You simply buy a small grounding rod and piece of grounding copper and leave it as dedicated, you can tie into the grounding rod for your house, etc. I have yet to ground mine. That said, ground it. This information is marginally correct and dangerous! Short answer? YES it needs to be grounded, but the details of how/where are IMPORTANT! By code, there is to be a SINGLE bonding point between Neutral and Earth-Ground, this is almost always in the Main Panel. Some generators have a "floating neutral" while others have a "bonded neutral". When you are connecting the genny to your Main Panel via an interlock kit, you will be grounding the generator through the ground wire fed through the cable from your panel. If you have a "floating neutral" that's all you need to worry about; the generator is grounded AND you only have one bonding location. If you're generator has a "bonded neutral", you need to break the bond which will require some rewiring on the generator. If you have more than one bonding point, you increase the chance of the ground & neutral wires carrying voltage which would mean touching anything metal & grounded could result in a shock. Many portable generators come with bonded neutral since they're primarily intended to be used with extension cords and the neutral & ground need to be bonded in this situation. When used in this manner, you would (and OSHA requires) need to provide a ground point at the generator. |
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Quoted: So how to know if your generator has a "bonded neutral" or "floating neutral" ? And if your setup includes a transfer switch, then you are using the ground in the panel? Is that correct? The generator will be labeled bonded vs. floating either on the unit or in the manual. Barring that, you can remove the outlet covers and look for a jumper wire between ground & neutral; note that you may need a wiring schematic to be certain of this method... Unless a more knowledgeable electrician can determine otherwise, there's still to be only a single bonding point for Earth-Ground & Neutral. You can change the location of it to some degree, but never should you have more than one bond point. ETA: Forgot to answer that... Yes the transfer switch will use the ground from the main panel. The transfer switch is really nothing more than a sub-panel with an interlock on every breaker. Unless of course you're referring to a service rated transfer switch; those are installed ahead of the main panel and are wired accordingly. |
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Quoted: The generator will be labeled bonded vs. floating either on the unit or in the manual. Barring that, you can remove the outlet covers and look for a jumper wire between ground & neutral; note that you may need a wiring schematic to be certain of this method... Unless a more knowledgeable electrician can determine otherwise, there's still to be only a single bonding point for Earth-Ground & Neutral. You can change the location of it to some degree, but never should you have more than one bond point. ETA: Forgot to answer that... Yes the transfer switch will use the ground from the main panel. The transfer switch is really nothing more than a sub-panel with an interlock on every breaker. Unless of course you're referring to a service rated transfer switch; those are installed ahead of the main panel and are wired accordingly. Quoted: Quoted: So how to know if your generator has a "bonded neutral" or "floating neutral" ? And if your setup includes a transfer switch, then you are using the ground in the panel? Is that correct? The generator will be labeled bonded vs. floating either on the unit or in the manual. Barring that, you can remove the outlet covers and look for a jumper wire between ground & neutral; note that you may need a wiring schematic to be certain of this method... Unless a more knowledgeable electrician can determine otherwise, there's still to be only a single bonding point for Earth-Ground & Neutral. You can change the location of it to some degree, but never should you have more than one bond point. ETA: Forgot to answer that... Yes the transfer switch will use the ground from the main panel. The transfer switch is really nothing more than a sub-panel with an interlock on every breaker. Unless of course you're referring to a service rated transfer switch; those are installed ahead of the main panel and are wired accordingly. My house (that was "professionally" re-wired before we bought it) has 3 ground rods in various places. Should I call an electrician in?
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Quoted: Explain this singular bonding point a little more to me. As in there should only by 1 grounding rod for a house? My house (that was "professionally" re-wired before we bought it) has 3 ground rods in various places. Should I call an electrician in? No, no. The singular bonding point is in reference the the bonding of the neutral & ground bus bars in the main panel. It is permissible to electrically join the neutral & ground in only a single location, usually this is done in the main panel. |
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My house (that was "professionally" re-wired before we bought it) has 3 ground rods in various places. Should I call an electrician in? They should all be bonded together. If they are not, it creates a potential hazard, although the potential is limited. it is not unheard of for this situation though to result in damage to satellite TV, cable TV, or telephone systems. I find this ironic since it is often these very suppliers that in the past have added unbonded ground rods for some reason. these days the code requires an intersystem bonding connection that these low voltage systems can be grounded to that gets rid of this problem. Most of the time, generators that have built in receptacles are listed by UL and UL requires a factory bond between the generator frame and neutral at the generator. This is because these style of generators are intended to be used standalone. often the bond is accessible and can be removed, but then it would not be safe if you went back to using it alone. |
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For 99% it doesn't matter.
The last time this came up, it degenerated into ship's electrical, floating grounds, and battle short. The best practices of an Army guy who has worked on them are going to be different from an NEC electrical guy or a sub-sailor. My .02: -if you're plugging in after a storm every few years, you prob will never notice a difference...don't bother. -if you're putting something in a permanent spot for prolonged operation, a genny ground rod will be "safer" for a few reasons that some will debate. You may have some kind of extra rods for lightning protection, don't be alarmed. |
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For 99% it doesn't matter. The last time this came up, it degenerated into ship's electrical, floating grounds, and battle short. It was kind of humorous watching the clueless make stuff up as they went that had little to do with the issue at hand. The best practices of an Army guy who has worked on them are going to be different from an NEC electrical guy or a sub-sailor. Army requires NEC be followed these days for stuff that is actually installed. Portable stuff is something else. My .02: -if you're plugging in after a storm every few years, you prob will never notice a difference...don't bother. Won't matter any. -if you're putting something in a permanent spot for prolonged operation, a genny ground rod will be "safer" for a few reasons that some will debate. perhaps you would be willing to enlighten us on just what those few reasons might be. You may have some kind of extra rods for lightning protection, don't be alarmed. It does not matter why they are there. they are supposed to be bonded together. OTOH, it probably will not matter. people obsess way too much about ground rods which do very little to add any level of safety at all to most residential electrical installations but do stupid crap that is totally unsafe, usually because they just do not know any better, and worse, do not know enough to know they do not know, so they often listen to others who do not know. |
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Quoted: My house (that was "professionally" re-wired before we bought it) has 3 ground rods in various places. Should I call an electrician in? Quoted: Quoted: Explain this singular bonding point a little more to me. As in there should only by 1 grounding rod for a house? My house (that was "professionally" re-wired before we bought it) has 3 ground rods in various places. Should I call an electrician in? No, no. The singular bonding point is in reference the the bonding of the neutral & ground bus bars in the main panel. It is permissible to electrically join the neutral & ground in only a single location, usually this is done in the main panel. ETA: Or is this more of a matter of when you tie your house into your panel rather than run extension cords? ETA 2: I just re-read the OP, and I see that tying into the mains is what he is talking about. Totally missed that fist time around. I did probably give bad advise. |
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Let me make sure I'm using the correct terminology.
I am going to feed the generator output through a 30-amp breaker that I installed as part of a kit that I bought. The cord from the generator to the house has four conductors. In order to supply power to the house I have to manually turn all breakers off, throw the main breaker, 200-amps, to the off position, and only then I am able to turn the 30-amp breaker on. I think I am really not feeding from the mains, i.e. the drop from the overhead lines. Finally, the generator does have a small stud which is labeled 'ground'. P |
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Quoted: Let me make sure I'm using the correct terminology. I am going to feed the generator output through a 30-amp breaker that I installed as part of a kit that I bought. The cord from the generator to the house has four conductors. In order to supply power to the house I have to manually turn all breakers off, throw the main breaker, 200-amps, to the off position, and only then I am able to turn the 30-amp breaker on. I think I am really not feeding from the mains, i.e. the drop from the overhead lines. Finally, the generator does have a small stud which is labeled 'ground'. P Reference the posts above about the neutral bonding; check your generator output for a bond wire between neutral & ground and remove it. Is, if you have a meter, there should be NO continuity between the neutral & ground terminals on the output of the generator. Obviously with plugs disconnected and the generator OFF. The generator will source it's ground through the 4 wire plug.
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My generator has built in receptacles and a hook up for a transfer switch. The neutral floats. They recommend grounding the generator when using the receptacles. When hooking to a transfer switch it uses the ground at the panel. This much I know for certain, you never want 2 different grounds. All ground rods should be bonded together. |
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This thread is of interest, because in the past week, getting ready for winter, I ran conduit from two gennies, an MQ Whisperwatt 25 kw 3 phase and a light tower genny, it's 6000 watts 240/120 single phase.
The install is off grid. The conduit terminates in the 'barn'. The reason I need 3 phase is for a mill, lathe, bandsaw and welder, altho it also can run on single phase but I feel the light tower is a little small to run it. [Five wires for the 25kw genny, U,V,W the 3 208 vac phases and, O neutral, and gnd.] A selector inside the genny allows the wiring to be switched to 120/240 vac single phase and then uses just 4 of the wires] 480/277 3 phase is also available from the MQ but I've got no ap for it. Another reason is to run a modest air compressor, that the 1800 watt inverter on the solar system doesn't like to won't start and the light tower genny also won't start running on one side of it's 240 balanced output. Plus, I don't know but suspect running a max load on one side of the light tower's genny winding might be a bad idea as far as the life of the genny. A bit more background... The light tower 6kw 120/240 genny that won't start the compressor on 1/2 of its alternator, so I connected the little 6kw genny to an 'auto transformer' rated at about 6000 watts. [I'll do a topic on auto transformers maybe because sometimes they can be found for less than the cost of a used 'regular transformer' and I think, are more efficient, since some windings are eliminated. I found a nice one almost free.  They are abt 14" by 10" by 8" and weigh abt 25 pounds or maybe a little more.
Measuring the losses thru the auto transformer under a 120 vac 15 amp load seems to bear this out. Parasitic losses IIRC were less than one amp with a Fluke clamp on but I need to run it w/out load and see how much it warms up to get a better idea because of the difficulty for me to visualize what's going on with the windings connected to neutral at the center and possible imbalances elsewhere -genny... The auto transformer takes the 240 from the genny into two of its windings in series and 120 is taken off one of the windings. The windings are heavy and this transformer is designed to be used this way. Neutral from the genny is connected to the connection of the two windings W1 and W3 let's call them and the 120 out is taken from that junction and the other side one of the windings. This allows approx a full 6000 watts of 120 vac, altho some are most likely to debate this... 
So, all the wiring is into the barn, the little genny is hooked to the transformer, the transformer feeds a small load 'box' with capacity for 2 breakers [box is a hell od a deal at ~$12 at box stores and GE half space breakers are ~$6] This little load center is perfect for a small solar system in that the source and output of the solar controller can be switched independently, and breakers up to 30 amps can be installed. [Subject for another topic] Now, my decision is to break the 2 genny frames from neutral inside both gennies or to leave them connected. The gennys are spaced about 20 feet apart. One is abt 15 feet from the metal bldg and the other is further away. I WILL bond neutral and gnd from both at their respective termination panels in the barn and attach those points to the building. The issue in my mind, irrespective of code, is what difference does it make if the frame assembly of the genny outside, that is bonded to the building and inside wiring panel, gets -or doesn't- its neutral isolated inside the genny? Sure there are two possible paths for the neutral TO THE genny structure if I don't unbond it [the 'white' wire from the load center, and the gnd wire from the barn via the genny's internal jumper] But what are the safety failure mode issues of leaving the neutral and gnd bonded in the gennies316???? |
8. What does a "grounded electrical power distribution system" refer to?The National Electrical Code (NEC) requires the use of a "grounded electrical distribution system" for a permanently connected AC power source. As per this system, one of the two current-carrying conductors is required to be grounded. This grounded conductor is called the "Neutral / Cold / Return". As this conductor is bonded to earth ground, it will be at near zero voltage or potential. There is no risk of electrical shock if this conductor is touched. The other current carrying conductor is called the "Line / Live / Hot". The connection between the "Neutral" and the grounding electrode conductor is made only at one point in the system. This is known as the system ground. This single point connection (bond) is usually made in the service entrance or in the load center. If this connection is inadvertently made in more than one place, then unwanted currents will flow in the equipment grounding conductors. These unwanted currents may cause inverters and charge controllers to be unreliable and may interfere with the operation of ground-fault detectors and over-current devices NOTE: In a single phase AC power source, a current-carrying conductor that is not bonded to the earth ground cannot be called a "neutral". This conductor will be at an elevated voltage with respect to the earth ground and may produce electrical shock when touched. From: http://www.samlexamerica.com/support/faqs/faq16.aspx Note the section I've underlined. If more than one neutral-ground bond is made, there can be a potential difference can build between Neutral & Ground; potential difference = voltage. That means touching a grounded item or the neutral wire could result in a shock! FYI, since you're dealing with a transformer you may need an additional neutral-ground bond. I'm not entirely clear on how you set up your wiring, but most transformers isolate the secondary neutral from the bonded ground on the primary side due to the nature of the device. As such, your secondary side neutral may not have a ground reference and could carry voltage. |
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From: http://www.samlexamerica.com/support/faqs/faq16.aspx Note the section I've underlined. If more than one neutral-ground bond is made, there can be a potential difference can build between Neutral & Ground; potential difference = voltage. That means touching a grounded item or the neutral wire could result in a shock! FYI, since you're dealing with a transformer you may need an additional neutral-ground bond. I'm not entirely clear on how you set up your wiring, but most transformers isolate the secondary neutral from the bonded ground on the primary side due to the nature of the device. As such, your secondary side neutral may not have a ground reference and could carry voltage. Quoted:
8. What does a "grounded electrical power distribution system" refer to?The National Electrical Code (NEC) requires the use of a "grounded electrical distribution system" for a permanently connected AC power source. As per this system, one of the two current-carrying conductors is required to be grounded. This grounded conductor is called the "Neutral / Cold / Return". As this conductor is bonded to earth ground, it will be at near zero voltage or potential. There is no risk of electrical shock if this conductor is touched. The other current carrying conductor is called the "Line / Live / Hot". The connection between the "Neutral" and the grounding electrode conductor is made only at one point in the system. This is known as the system ground. This single point connection (bond) is usually made in the service entrance or in the load center. If this connection is inadvertently made in more than one place, then unwanted currents will flow in the equipment grounding conductors. These unwanted currents may cause inverters and charge controllers to be unreliable and may interfere with the operation of ground-fault detectors and over-current devicesNOTE: In a single phase AC power source, a current-carrying conductor that is not bonded to the earth ground cannot be called a "neutral". This conductor will be at an elevated voltage with respect to the earth ground and may produce electrical shock when touched. From: http://www.samlexamerica.com/support/faqs/faq16.aspx Note the section I've underlined. If more than one neutral-ground bond is made, there can be a potential difference can build between Neutral & Ground; potential difference = voltage. That means touching a grounded item or the neutral wire could result in a shock! FYI, since you're dealing with a transformer you may need an additional neutral-ground bond. I'm not entirely clear on how you set up your wiring, but most transformers isolate the secondary neutral from the bonded ground on the primary side due to the nature of the device. As such, your secondary side neutral may not have a ground reference and could carry voltage. I wonder who writes this stuff. In a residential system, the grounded conductor is required to be the neutral if you have a typical 3 wire system (i.e.-240/120). there is just no way around it. neutral is not the same thing as grounded conductor, although in a 120/240 3 wire system like in most residences, the neutral is the grounded conductor. as for risk of shock, I can't even begin to tell you what a bad idea it is to tell amateurs that they can safely touch the white wire. its a bad idea for people that know what they are doing. |
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From: http://www.samlexamerica.com/support/faqs/faq16.aspx Note the section I've underlined. If more than one neutral-ground bond is made, there can be a potential difference can build between Neutral & Ground; potential difference = voltage. That means touching a grounded item or the neutral wire could result in a shock! FYI, since you're dealing with a transformer you may need an additional neutral-ground bond. I'm not entirely clear on how you set up your wiring, but most transformers isolate the secondary neutral from the bonded ground on the primary side due to the nature of the device. As such, your secondary side neutral may not have a ground reference and could carry voltage. Quoted:
8. What does a "grounded electrical power distribution system" refer to?The National Electrical Code (NEC) requires the use of a "grounded electrical distribution system" for a permanently connected AC power source. As per this system, one of the two current-carrying conductors is required to be grounded. This grounded conductor is called the "Neutral / Cold / Return". As this conductor is bonded to earth ground, it will be at near zero voltage or potential. There is no risk of electrical shock if this conductor is touched. The other current carrying conductor is called the "Line / Live / Hot". The connection between the "Neutral" and the grounding electrode conductor is made only at one point in the system. This is known as the system ground. This single point connection (bond) is usually made in the service entrance or in the load center. If this connection is inadvertently made in more than one place, then unwanted currents will flow in the equipment grounding conductors. These unwanted currents may cause inverters and charge controllers to be unreliable and may interfere with the operation of ground-fault detectors and over-current devicesNOTE: In a single phase AC power source, a current-carrying conductor that is not bonded to the earth ground cannot be called a "neutral". This conductor will be at an elevated voltage with respect to the earth ground and may produce electrical shock when touched. From: http://www.samlexamerica.com/support/faqs/faq16.aspx Note the section I've underlined. If more than one neutral-ground bond is made, there can be a potential difference can build between Neutral & Ground; potential difference = voltage. That means touching a grounded item or the neutral wire could result in a shock! FYI, since you're dealing with a transformer you may need an additional neutral-ground bond. I'm not entirely clear on how you set up your wiring, but most transformers isolate the secondary neutral from the bonded ground on the primary side due to the nature of the device. As such, your secondary side neutral may not have a ground reference and could carry voltage. The transformer is an auto-transformer and there is no secondary in the usual sense. As I explained, the neutral ftom the genny is connected to the center of the 2 'series' windings and is the common point for the bonding of any ground [aside from in the genny, that my question regarding safety failure modes, is all about] |
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I wonder who writes this stuff. In a residential system, the grounded conductor is required to be the neutral if you have a typical 3 wire system (i.e.-240/120). there is just no way around it. neutral is not the same thing as grounded conductor, although in a 120/240 3 wire system like in most residences, the neutral is the grounded conductor. as for risk of shock, I can't even begin to tell you what a bad idea it is to tell amateurs that they can safely touch the white wire. its a bad idea for people that know what they are doing. Quoted:
Quoted:
8. What does a "grounded electrical power distribution system" refer to?The National Electrical Code (NEC) requires the use of a "grounded electrical distribution system" for a permanently connected AC power source. As per this system, one of the two current-carrying conductors is required to be grounded. This grounded conductor is called the "Neutral / Cold / Return". As this conductor is bonded to earth ground, it will be at near zero voltage or potential. There is no risk of electrical shock if this conductor is touched. The other current carrying conductor is called the "Line / Live / Hot". The connection between the "Neutral" and the grounding electrode conductor is made only at one point in the system. This is known as the system ground. This single point connection (bond) is usually made in the service entrance or in the load center. If this connection is inadvertently made in more than one place, then unwanted currents will flow in the equipment grounding conductors. These unwanted currents may cause inverters and charge controllers to be unreliable and may interfere with the operation of ground-fault detectors and over-current devicesNOTE: In a single phase AC power source, a current-carrying conductor that is not bonded to the earth ground cannot be called a "neutral". This conductor will be at an elevated voltage with respect to the earth ground and may produce electrical shock when touched. From: http://www.samlexamerica.com/support/faqs/faq16.aspx Note the section I've underlined. If more than one neutral-ground bond is made, there can be a potential difference can build between Neutral & Ground; potential difference = voltage. That means touching a grounded item or the neutral wire could result in a shock! FYI, since you're dealing with a transformer you may need an additional neutral-ground bond. I'm not entirely clear on how you set up your wiring, but most transformers isolate the secondary neutral from the bonded ground on the primary side due to the nature of the device. As such, your secondary side neutral may not have a ground reference and could carry voltage. I wonder who writes this stuff. In a residential system, the grounded conductor is required to be the neutral if you have a typical 3 wire system (i.e.-240/120). there is just no way around it. neutral is not the same thing as grounded conductor, although in a 120/240 3 wire system like in most residences, the neutral is the grounded conductor. as for risk of shock, I can't even begin to tell you what a bad idea it is to tell amateurs that they can safely touch the white wire. its a bad idea for people that know what they are doing. "I wonder who writes this stuff." My guess is folks who have a fundamental understanding of the code book... But little 'practical' understanding of the deeper technical and applied issues, other than bending conduit, mounting NEMA boxes, and twisting wires together ---generally. There are certainly exceptions, but of all the electricians I've known, they have some rather confused interpretations of technical reality, that they are unable to resolve from their world of 'electrical fantasy'.
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Quoted: I wonder who writes this stuff. In a residential system, the grounded conductor is required to be the neutral if you have a typical 3 wire system (i.e.-240/120). there is just no way around it. neutral is not the same thing as grounded conductor, although in a 120/240 3 wire system like in most residences, the neutral is the grounded conductor. as for risk of shock, I can't even begin to tell you what a bad idea it is to tell amateurs that they can safely touch the white wire. its a bad idea for people that know what they are doing. Quoted: Quoted: 8. What does a "grounded electrical power distribution system" refer to?The National Electrical Code (NEC) requires the use of a "grounded electrical distribution system" for a permanently connected AC power source. As per this system, one of the two current-carrying conductors is required to be grounded. This grounded conductor is called the "Neutral / Cold / Return". As this conductor is bonded to earth ground, it will be at near zero voltage or potential. There is no risk of electrical shock if this conductor is touched. The other current carrying conductor is called the "Line / Live / Hot". The connection between the "Neutral" and the grounding electrode conductor is made only at one point in the system. This is known as the system ground. This single point connection (bond) is usually made in the service entrance or in the load center. If this connection is inadvertently made in more than one place, then unwanted currents will flow in the equipment grounding conductors. These unwanted currents may cause inverters and charge controllers to be unreliable and may interfere with the operation of ground-fault detectors and over-current devicesNOTE: In a single phase AC power source, a current-carrying conductor that is not bonded to the earth ground cannot be called a "neutral". This conductor will be at an elevated voltage with respect to the earth ground and may produce electrical shock when touched. From: http://www.samlexamerica.com/support/faqs/faq16.aspx Note the section I've underlined. If more than one neutral-ground bond is made, there can be a potential difference can build between Neutral & Ground; potential difference = voltage. That means touching a grounded item or the neutral wire could result in a shock! FYI, since you're dealing with a transformer you may need an additional neutral-ground bond. I'm not entirely clear on how you set up your wiring, but most transformers isolate the secondary neutral from the bonded ground on the primary side due to the nature of the device. As such, your secondary side neutral may not have a ground reference and could carry voltage. I wonder who writes this stuff. In a residential system, the grounded conductor is required to be the neutral if you have a typical 3 wire system (i.e.-240/120). there is just no way around it. neutral is not the same thing as grounded conductor, although in a 120/240 3 wire system like in most residences, the neutral is the grounded conductor. as for risk of shock, I can't even begin to tell you what a bad idea it is to tell amateurs that they can safely touch the white wire. its a bad idea for people that know what they are doing. Quite frankly I only skimmed the stuff I quoted and never saw where it said it was OK to touch a wire in a live system...  Also I believe the section I quoted is only referencing residential 3-wire single phase systems, and I believe still complies with what you're saying. Having reread the information, it's rather confusing and somewhat misleading. It appears to be referring to single phase 120V, though it doesn't actually state that, since obviously a 240V run would be wired differently. |
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Quoted: The transformer is an auto-transformer and there is no secondary in the usual sense. As I explained, the neutral ftom the genny is connected to the center of the 2 'series' windings and is the common point for the bonding of any ground [aside from in the genny, that my question regarding safety failure modes, is all about] If I'm reading how you have this wired, the neutral effectively is "passed-thru" from the genny to the appliance side of the circuit with the auto-transformer using it as a reference voltage? You still need to bond neutral & ground together at some point. I think you're OK having the transformer output feed into your distribution panel as a 120V feed (3 wires; line, neutral, & ground). The bonding would be in the panel and the neutral-ground bond at the generator should be broken. |
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If I'm reading how you have this wired, the neutral effectively is "passed-thru" from the genny to the appliance side of the circuit with the auto-transformer using it as a reference voltage? You still need to bond neutral & ground together at some point. I think you're OK having the transformer output feed into your distribution panel as a 120V feed (3 wires; line, neutral, & ground). The bonding would be in the panel and the neutral-ground bond at the generator should be broken. Quoted:
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The transformer is an auto-transformer and there is no secondary in the usual sense. As I explained, the neutral ftom the genny is connected to the center of the 2 'series' windings and is the common point for the bonding of any ground [aside from in the genny, that my question regarding safety failure modes, is all about] If I'm reading how you have this wired, the neutral effectively is "passed-thru" from the genny to the appliance side of the circuit with the auto-transformer using it as a reference voltage? You still need to bond neutral & ground together at some point. I think you're OK having the transformer output feed into your distribution panel as a 120V feed (3 wires; line, neutral, & ground). The bonding would be in the panel and the neutral-ground bond at the generator should be broken. I guess so, sorta, but I'm missing the voltage reference issue, these aren't op amps... 
I'm lazy and WHY does the N/gnd bond in the genny need to be broken? The PRACTICAL/TECHNICAL reason, not what some book says... And aside from liability issues. |
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I'm lazy and WHY does the N/gnd bond in the genny need to be broken? The PRACTICAL/TECHNICAL reason, not what some book says... And aside from liability issues. It is considered undesirable to have any current at all flowing on the G wires under normal circumstances, especially past the service point. If you connect N-G at more than one point you will force current to flow in the G wires because you have placed the G wires in parallel with the N wires. How bad this is in real life is hard to say. Jack leg neutrals are pretty common and rarely kill people but they will cause GFCIs and AFCIs to trip. |
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It is considered undesirable to have any current at all flowing on the G wires under normal circumstances, especially past the service point. If you connect N-G at more than one point you will force current to flow in the G wires because you have placed the G wires in parallel with the N wires. How bad this is in real life is hard to say. Jack leg neutrals are pretty common and rarely kill people but they will cause GFCIs and AFCIs to trip. Quoted:
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I'm lazy and WHY does the N/gnd bond in the genny need to be broken? The PRACTICAL/TECHNICAL reason, not what some book says... And aside from liability issues. It is considered undesirable to have any current at all flowing on the G wires under normal circumstances, especially past the service point. If you connect N-G at more than one point you will force current to flow in the G wires because you have placed the G wires in parallel with the N wires. How bad this is in real life is hard to say. Jack leg neutrals are pretty common and rarely kill people but they will cause GFCIs and AFCIs to trip. OK, now we're getting somewheres. Can't do it today, but I'll see if there is any appreciable current flowing in the gnd/neutral wires from the genny when we go back up. Since the auto-former is fed balanced 240 vac, I expect it will be minimal. |
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Quoted: OK, now we're getting somewheres. Can't do it today, but I'll see if there is any appreciable current flowing in the gnd/neutral wires from the genny when we go back up. Since the auto-former is fed balanced 240 vac, I expect it will be minimal. Quoted: Quoted: Quoted: I'm lazy and WHY does the N/gnd bond in the genny need to be broken? The PRACTICAL/TECHNICAL reason, not what some book says... And aside from liability issues. It is considered undesirable to have any current at all flowing on the G wires under normal circumstances, especially past the service point. If you connect N-G at more than one point you will force current to flow in the G wires because you have placed the G wires in parallel with the N wires. How bad this is in real life is hard to say. Jack leg neutrals are pretty common and rarely kill people but they will cause GFCIs and AFCIs to trip. OK, now we're getting somewheres. Can't do it today, but I'll see if there is any appreciable current flowing in the gnd/neutral wires from the genny when we go back up. Since the auto-former is fed balanced 240 vac, I expect it will be minimal. On my light tower, there was a jumper wire under the cover of the generator head bonding neutral & ground. It was a quick 2 minutes to remove it; I have plans to place a switch in there so I can have it either way I want easily. Then I'm good when connected to my house panel AND when I'm powering loads at a jobsite. |
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Quoted:
On my light tower, there was a jumper wire under the cover of the generator head bonding neutral & ground. It was a quick 2 minutes to remove it; I have plans to place a switch in there so I can have it either way I want easily. Then I'm good when connected to my house panel AND when I'm powering loads at a jobsite. You really do not want the fault current to flow through the switch. in any case, this kind of arrangement is not permitted by code for good reasons. The connection to the frame needs to be more permanent. |
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Quoted: You really do not want the fault current to flow through the switch. in any case, this kind of arrangement is not permitted by code for good reasons. The connection to the frame needs to be more permanent. Quoted: Quoted: On my light tower, there was a jumper wire under the cover of the generator head bonding neutral & ground. It was a quick 2 minutes to remove it; I have plans to place a switch in there so I can have it either way I want easily. Then I'm good when connected to my house panel AND when I'm powering loads at a jobsite. You really do not want the fault current to flow through the switch. in any case, this kind of arrangement is not permitted by code for good reasons. The connection to the frame needs to be more permanent. I was afraid of that... Hadn't spent anymore time thinking about it beyond it being a hair brained idea. |
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Quoted:
I was afraid of that... Hadn't spent anymore time thinking about it beyond it being a hair brained idea. Quoted:
Quoted:
Quoted:
On my light tower, there was a jumper wire under the cover of the generator head bonding neutral & ground. It was a quick 2 minutes to remove it; I have plans to place a switch in there so I can have it either way I want easily. Then I'm good when connected to my house panel AND when I'm powering loads at a jobsite. You really do not want the fault current to flow through the switch. in any case, this kind of arrangement is not permitted by code for good reasons. The connection to the frame needs to be more permanent. I was afraid of that... Hadn't spent anymore time thinking about it beyond it being a hair brained idea. Ah, put a zip tie on it.
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It looks like we're going "there" after all.
-Grounding the gen frame (w/ a rod) allows any kind of chaffed wire, failure, etc to be shunted to ground (you don't become the path to ground) -reduces the chance of static during fueling operations (rare, but wshtf there is no FD coming to help) My opinion is based on installing 60k's to ALAM's, tents and acft maint and fueling. They are indeed different from a house, but I see no detractors. I saw quite a few issues with grounding vs bonding w/ 3 phase power..however the mil uses 5 conductor wire for gens in the field (3 ph, N, Gnd) and doesn't hook up to "homes" that have a neutral going to a pole and some transformer. As previously stated, my civ genny has no wires on the GND terminal of the "residential" jacks...none. Merely 2 hots and the neutral. If hacking in at a sub panel and backfeeding, as a ton of folks won't admit they do, then ensure your panel is compliant (no N to GND bond) and hook up to 2 hots and Neutral. There is no issue with grounding the frame w/ a rod that I can determine. ....or as 99% don't care, just use the nema plug and forget about it. PS: if you have a license and see something wrong with what I have said, please let me know the "dangers/physics", not just because it says so somewhere, but why...thanks |
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To the above poster- Adding a ground rod, might reduce the voltage, but it's frequently not enough to trip a 20A circuit breaker during a fault. A ground rod is the least prefered ground for a house. Say your ground resistance is 20 ohms- at 120V, you will get 6 amps of current flow- the ground wires will be energized with potentially lethal voltage, and the breaker will never trip. FWIW, 20 ohms is a satisfactory resistance per the NEC.
I'd recomend one of the two following scenerios. 1) Connect everything with cord and plugs, making sure all of the ground pins are intact on the cords (OSHA would have you ohm them, but 99% of the failures are the male pin breaking off. ) This is legal for temporary use. 2) Connect the generator to a branch circuit transfer switch (with a bunch of 15 or 20A breakers) or a whole house switch between the utility and the main service disconnect. Or a main breaker interlock kit. Either way preserves the houses ground connection and the utility's ground/neutral connection, giving you a decent ground. As to if you keep the bond at the generator, I could care less. If the owner of the generator is country_boy, I am required NOT to bond the neutral and ground. If the same YDG3700 is owned by Alabama Power, then the bond IS required. I've extensivally studied calculus, physics, and electrical engineering, and I can find not evidence that the electrons are aware of who made them move, thus are going to follow the same path regardless of who the owner of record of the generator is. If however, you do not have the bond, you need 4 wire cable, which is more expensive. I choose to leave the bond in place, and use 4 wire cable. When I've placed the generator elsewhere, I've used 3 wire cable because I have 150' of 3-6 and only 60' of 8-4 (That might not sound like much, but it's over $1000 in cable) The "risk" from a bonded generator is as follows: The neutral curren that would otherwise return on the white is split between the white and green. The slight voltage drop across this wire will mean the frame of the generator might be several volts higher then true ground, and if you stand in a water puddle while touching the generator, you will have several volts across you body. As a result NEC wants the bond gone in some cases, and the NESC wants it present in others. Since the neutral only carried the imballance between phase conductors (12 A on red, and 10 on black means 2A on neutral) the risk is low. And its the same risk your child takes if they wake up to a power pole barefoot. At work we deploy dozens to hundreds of small generators after hurricanes- and almost all are wired with 3 conductor cable, and the generator bond is left alone. We have large trailer mounted generators with the bond intentionally in place also. These usually get a cadweld connection to our counterpoise except in emergencies |
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Quoted:
It looks like we're going "there" after all. -Grounding the gen frame (w/ a rod) allows any kind of chaffed wire, failure, etc to be shunted to ground (you don't become the path to ground) -reduces the chance of static during fueling operations (rare, but wshtf there is no FD coming to help) Neutral. There is no issue with grounding the frame w/ a rod that I can determine. The following comments assume that by grounding you mean an actual connection to earth. This seems reasonable to me, since it is what it actually means, but one never really knows what someone thinks it means. You just plain cannot "shunt" electricity to ground. Electricity, and residential electrical systems do not work that way. Period. If you do not understand that very basic fact about electricity nothing anyone says about it that is in fact true will make any sense to you. I agree that connecting any number of ground rods to the frame of a generator will not hurt anything. it won't do any good at all, but it will not harm anything. |
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Quoted: The following comments assume that by grounding you mean an actual connection to earth. This seems reasonable to me, since it is what it actually means, but one never really knows what someone thinks it means. You just plain cannot "shunt" electricity to ground. Electricity, and residential electrical systems do not work that way. Period. If you do not understand that very basic fact about electricity nothing anyone says about it that is in fact true will make any sense to you. I agree that connecting any number of ground rods to the frame of a generator will not hurt anything. it won't do any good at all, but it will not harm anything. Quoted: Quoted: It looks like we're going "there" after all. -Grounding the gen frame (w/ a rod) allows any kind of chaffed wire, failure, etc to be shunted to ground (you don't become the path to ground) -reduces the chance of static during fueling operations (rare, but wshtf there is no FD coming to help) Neutral. There is no issue with grounding the frame w/ a rod that I can determine. The following comments assume that by grounding you mean an actual connection to earth. This seems reasonable to me, since it is what it actually means, but one never really knows what someone thinks it means. You just plain cannot "shunt" electricity to ground. Electricity, and residential electrical systems do not work that way. Period. If you do not understand that very basic fact about electricity nothing anyone says about it that is in fact true will make any sense to you. I agree that connecting any number of ground rods to the frame of a generator will not hurt anything. it won't do any good at all, but it will not harm anything. I must be missing something. Why are ground rods used if not to shunt electricity to ground? I know they work to shunt electricity to ground during a lightning strike and when working on live equipment you try to insulate yourself from ground in case of an accidental shock. I've always thought they were to provide a path of least resistance to earth ground. I was reading about the dangers of having antennas and radio equipment connected to separate disconnected ground rods when lightning strikes. Lighting can hit the power lines and if the radio equipment has a better path to ground, it will come though your house wiring to the equipment grounding, some of the current bypassing the ground rods on the utility pole and service entrance. If they work to shunt lightning to ground why wouldn't electricity from a residential system or generator behave the same? http://www.w8ji.com/station_ground.htm |
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I must be missing something. Why are ground rods used if not to shunt electricity to ground? I know they work to shunt electricity to ground during a lightning strike and when working on live equipment you try to insulate yourself from ground in case of an accidental shock. I've always thought they were to provide a path of least resistance to earth ground. Quoted:
I must be missing something. Why are ground rods used if not to shunt electricity to ground? I know they work to shunt electricity to ground during a lightning strike and when working on live equipment you try to insulate yourself from ground in case of an accidental shock. I've always thought they were to provide a path of least resistance to earth ground. This kind of thing is a basic misconception held by many, including those who should know better. The SOLE purpose of grounding (connecting an electrical system to earth) is to attempt to keep the voltage of your electrical system with respect to earth at a constant value. This is actually in article 250.4(A) of the NEC. Electrical systems that
are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation. That is it. Period. fact - if a residential electrical system is grounded properly, the earth is NOT part of the fault clearing path. fact - even if the earth was part of the fault clearing path, there is nothing in the electrical code that requires it to be a good enough current carrying path that it could actually clear a fault. there is no specific performance specification for the earth connection. some people think it is 25 Ohms, but if you read the NEC carefully, it never actually says that anywhere. In any case if you had a 25 Ohm resistance on a 120V ground fault, you would only have a fault current of less than 5A which would never trip any residential circuit breaker. |
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I'm sure it's been asked but I'm lazy today so I am not going to search. Portable generator, which will be attached to power mains via interlock assembly. Do I still need to supply a ground for the generator by physically attaching it to the ground rod for the house? Can I drive a ground rod next to the generator and use that? Thanks. P I can tell you what WILL happen if you forget or dont. I messed up on a 4 pole twistlock and didnt verify the wiring prior to running it. I made a rookie mistake. in the house while i was doing a test run i had line power off and was running the whole house off the generator (8kw) i noticed the lights were brighter,,, Hmmmm. i got out the fluke and checked the wall outlet, 160vac
then things started poping, blew up 3 UPS and a few surge suppressors and power strips. blew up the garage door opener. So YES. it absolutely does have to be grounded.
that was an expensive lesson. I have been doing commercial and industrial electrical all my life, 20 yrs or so. first time i admitted to this one. the anonymity of arfcom |
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I can tell you what WILL happen if you forget or dont. I messed up on a 4 pole twistlock and didnt verify the wiring prior to running it. I made a rookie mistake. in the house while i was doing a test run i had line power off and was running the whole house off the generator (8kw) i noticed the lights were brighter,,, Hmmmm. i got out the fluke and checked the wall outlet, 160vac
then things started poping, blew up 3 UPS and a few surge suppressors and power strips. blew up the garage door opener. So YES. it absolutely does have to be grounded.
that was an expensive lesson. I have been doing commercial and industrial electrical all my life, 20 yrs or so. first time i admitted to this one. the anonymity of arfcom Quoted:
Quoted:
I'm sure it's been asked but I'm lazy today so I am not going to search. Portable generator, which will be attached to power mains via interlock assembly. Do I still need to supply a ground for the generator by physically attaching it to the ground rod for the house? Can I drive a ground rod next to the generator and use that? Thanks. P I can tell you what WILL happen if you forget or dont. I messed up on a 4 pole twistlock and didnt verify the wiring prior to running it. I made a rookie mistake. in the house while i was doing a test run i had line power off and was running the whole house off the generator (8kw) i noticed the lights were brighter,,, Hmmmm. i got out the fluke and checked the wall outlet, 160vac
then things started poping, blew up 3 UPS and a few surge suppressors and power strips. blew up the garage door opener. So YES. it absolutely does have to be grounded.
that was an expensive lesson. I have been doing commercial and industrial electrical all my life, 20 yrs or so. first time i admitted to this one. the anonymity of arfcom sounds like an open neutral. grounding or not would have NO effect on voltage L-N or L-L. |