Posted: 1/12/2012 10:34:28 AM EDT
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Hi Folks:
Can someone please explain to me the difference between a bonded or floating neutral, as it pertains to powering a home with a generator? I am looking at a generator which has a bonded nuetral. Thanks in advance. Stay Safe, AGreyMan |
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http://members.rennlist.org/warren/generator.html
Some generators use GFCI breakers to feed the AC outlets. When connected to a panel that does not switch neutral the GFCI breaker will trip immediately. The affected generators have the neutral conductor bonded to ground to pass OSHA job requirements. Home or building electrical panels also have the neutral bonded to ground. This dual bond supplies two paths for return current to flow. The GFCI breaker will detect a difference in neutral vs line current flow and open the circuit.
To remedy this problem, the generator must be changed to supply a floating neutral or the transfer panel rewired to switch neutral. If the generator neutral is changed, the "NEUTRAL BONDED TO FRAME" label must be replaced with a "NEUTRAL FLOATING" or "NEUTRAL NOT BONDED TO FRAME" label. The generator will no longer pass OSHA job requirements. There are four possible ground / neutral bond and transfer panel configurations. * Neutral bonded at generator, neutral switched at transfer panel. This is a correct configuration. Neutral for backup circuits will be isolated at the transfer panel and bonded within the generator. There will be no ground conductor current. This requires a three pole transfer switch. * Neutral floating at generator, neutral not switched at transfer panel. This is a correct configuration. Neutral for the entire system is bonded at the main service panel. There will be no ground conductor current. Only live lines are switched with a two pole transfer switch. * Neutral bonded at generator, neutral not switched at transfer panel. This seems to be the most common connection technique based on my research. Unfortunately it is not correct. Neutral will be connected to ground at the main panel and at the generator. Neutral current flow will flow along the ground conductor and through the generator chassis. This creates a potential shock hazard as the chassis becomes part of the current carrying circuit. The easiest way to fix the problem is to use a floating neutral generator or make the required changes to the generator internal wiring. * Neutral floating at generator, neutral switched at transfer panel. The neutral conductor has no ground reference. The neutral should be bonded within the generator or the transfer switch rewired to not switch the neutral conductor. Basically your generator is designed for job site power where you also need a grounding rod. It's usually not hard to go from a bonded to floating neutral. My generator (Champion) takes 10-15 minutes to swap back and forth. |
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Thanks for the prompt and helpful respone.
Any ideas about how I would go about making that change from bonded to floating? I am not un-handy in things mechanical, and I have even done a little electrical work, but this seems to be beyond my familiarity. Essentially the neutral and the ground are tied together somewhere in the generator wiring? If I trace the wiring back from the NEMA L14-30 plug, the two hots and the nuetral should go to the gen head istelf, right? Where should the ground go if I want a floating ground? Not disconnected all together? Generator manual can be found here: Powerhorse Manual Again, thanks to anyone for any pointers. Stay Safe, AGreyMan |
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I wouldn't sweat it Use decent sized cable from the generator to the transfer switch. The voltage on the generator frame will be 1/2 the voltage drop across a normal neutral (ie a couple of volts). And in most cases, the neutral is carrying less current than either "hot" conductor. I'd only worry about it if the cable to the transfer switch was really long, and even then, it's probally academic. I had a site in Ga where GPCO had some major harmonic issues, and our neutral was running 24V above ground floating, and 12V bonded (the 12V was because they were flowing 10 A I think it was into our 1.2 ohm ground system. Even with all of the conduits, panels, outlet covers, etc, 12V hotter then earth ground, no one noticed. We had some major noise issues thought.
If you pull open the generator, you will see some sort of a bond between the green wire and the white wire, likely a fascon terminal. This can be disconnected. It is only needed to cause a GFCI (either in the generator or external to the generator) to trip. I'd worry more about disconnecting the bond, forgetting about it and then a GFCI not tripping on a faulty tool. There's no AC wiring diagram in the manual you posted, but the bond could be at any of the recepticals, or at the generator. there is a semi suspicious terminal with 2 wires on it in the drawing behing the middle of the control pannel. With utility power systems you worry about bolted faults and such, even with big generators. In this case if a bolted fault doesn't trip the breaker, the engine will kill the load. BTW, non of this should be applied to agricultural operations. Even a few volts will cause issues with animals . But we wear shoes and don't lick our tools and appliances, |
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Quoted:
Thanks for the prompt and helpful respone. Any ideas about how I would go about making that change from bonded to floating? I am not un-handy in things mechanical, and I have even done a little electrical work, but this seems to be beyond my familiarity. Essentially the neutral and the ground are tied together somewhere in the generator wiring? If I trace the wiring back from the NEMA L14-30 plug, the two hots and the nuetral should go to the gen head istelf, right? Where should the ground go if I want a floating ground? Not disconnected all together? Generator manual can be found here: Powerhorse Manual Again, thanks to anyone for any pointers. Stay Safe, AGreyMan Here's how my Champion goes from bonded to floating. http://www.championpowerequipment.com/pdf/tech-bulletins/neutral_bonding-6_10_2007.pdf I'd make a guess that your generator may be similar. You'll start by removing the end cover of the generator head (page 52, item 5). Since it's UL certified the wire colors will be standard. |
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Quoted:
Quoted:
Thanks for the prompt and helpful respone. Any ideas about how I would go about making that change from bonded to floating? I am not un-handy in things mechanical, and I have even done a little electrical work, but this seems to be beyond my familiarity. Essentially the neutral and the ground are tied together somewhere in the generator wiring? If I trace the wiring back from the NEMA L14-30 plug, the two hots and the nuetral should go to the gen head istelf, right? Where should the ground go if I want a floating ground? Not disconnected all together? Generator manual can be found here: Powerhorse Manual Again, thanks to anyone for any pointers. Stay Safe, AGreyMan Here's how my Champion goes from bonded to floating. http://www.championpowerequipment.com/pdf/tech-bulletins/neutral_bonding-6_10_2007.pdf I'd make a guess that your generator may be similar. You'll start by removing the end cover of the generator head (page 52, item 5). Since it's UL certified the wire colors will be standard. I looks like the instructions are taping off [disconnecting] the neutral and leaving it floating. In this instance you won't be able to draw power for anything but 220 volt loads from the gen head. Because the 110 volt loads are 'pulled' from the neutral and one or the other 'hot' terminals and both the neutral and two 'hot' wires from the gen head are fed to the duplex outlets, etc. So those instructions make no sense to me for the application being discussed but I may well be missing something. |
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Quoted:
Thanks for the prompt and helpful respone. Any ideas about how I would go about making that change from bonded to floating? I am not un-handy in things mechanical, and I have even done a little electrical work, but this seems to be beyond my familiarity. Essentially the neutral and the ground are tied together somewhere in the generator wiring? If I trace the wiring back from the NEMA L14-30 plug, the two hots and the nuetral should go to the gen head istelf, right? Where should the ground go if I want a floating ground? Not disconnected all together? Generator manual can be found here: Powerhorse Manual Again, thanks to anyone for any pointers. Stay Safe, AGreyMan I put a 30-amp 120v switch on my troybilt. ON = Bonded for portable use OFF - Unbonded for home use |
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Quoted:
I looks like the instructions are taping off [disconnecting] the neutral and leaving it floating. In this instance you won't be able to draw power for anything but 220 volt loads from the gen head. Because the 110 volt loads are 'pulled' from the neutral and one or the other 'hot' terminals and both the neutral and two 'hot' wires from the gen head are fed to the duplex outlets, etc. So those instructions make no sense to me for the application being discussed but I may well be missing something. EXPY, thats just a bond they are removing, like the wire between the neutral and ground bus bars in an electrical pannel. Elsewhere the white should also be connected to the the center of the generator windings. |
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So, when I get the generator, I'll dig into it a bit, and see how to disconnect the bond.
But if I understand Country Boy, in a application like this, it is not critical that the neutral is floating? Stay Safe, Matt Edited to add: Thanks a lot, folks. I really appreciate all the advice and insight we help each other with here. Hopefully I can someday help somebody out! |
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Quoted:
So, when I get the generator, I'll dig into it a bit, and see how to disconnect the bond. But if I understand Country Boy, in a application like this, it is not critical that the neutral is floating? Stay Safe, Matt Edited to add: Thanks a lot, folks. I really appreciate all the advice and insight we help each other with here. Hopefully I can someday help somebody out! If you want to comply with the NEC you will be sure your neutral and ground are bonded in only one place. If there was a fire your insurance company might investigate and if they can suggest that the floating neutral was the problem you might have trouble getting your claim completed. Also, while we do wear shoes and dont tend to lick electrical appliances, we do sometimes set the generator outside in snow, ice, or wet ground and sometimes we are also wet, tired, or had a few beers when we hook up our generators. Doing it right will keep us and our property safe. |
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Quoted:
If you want to comply with the NEC you will be sure your neutral and ground are bonded in only one place. If there was a fire your insurance company might investigate and if they can suggest that the floating neutral was the problem you might have trouble getting your claim completed. Also, while we do wear shoes and dont tend to lick electrical appliances, we do sometimes set the generator outside in snow, ice, or wet ground and sometimes we are also wet, tired, or had a few beers when we hook up our generators. Doing it right will keep us and our property safe. I'm note sure if a cord and plug generator is covered by the NEC, that is a big gray area, since both the cord and plug, and the generator are temporary. It is obviously not the intent of the NEC for you tyo have 2 bonds.. Note the service entrance into your house is wired the same way. the power company uses a single pair of conductors (or a single conductor) for both ground and neutral. AFAIK, the power companies have never been sued due to their use of a bonded neutral (and in fact, they are supplying your house the 99.9% of the time. Note, I go and buy a 2400-120/240 transformer. If I own the transformer then per the NEC, their should only be one ground connection (at the service entrance panel). There are a few exceptions in Article 250. However, if the local utility installes the same transformer, they are required to biond the neutral and ground at the transformer, and again the NEC requires it in the service entrance pannel. So one obvious solution is to paint on the generator "Property of A Gray Woman Electric Company." Now you meet the NEC As to licking the generator, you will feel a tingle, maybe. Both humans and animals will not want to feel that again. For animals, they will reduce their intake of food and water. For most of us, we'd quit lcking the generator. Touching a generator, even with wet feet, should not give a shock. Intact skin has a much higher resistance. I've never heard of anyone getting shocked by a 12V car battary, and that is far more voltage then you will ever get on this neutral. Like I said, we had a facility that was floating 24V above ground, and no one noticed. GPCO even denied there was a safety hazard (I somewhat disagree, there was a minor fire hazared,as we could put 6amps onto the telephone cable shield, which could cause a fire. Right now the voltage in my house between the neutral and ground is 0.3V. Thats for a 3/0 cable going about 300'. 30' of 12ga would be less thern twice that (The 12 white and 12 green together equal a 9 ga conductor, a 3/0 has about 1/16 the resistance of a 9 ga wire. |
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Quoted:
Quoted:
I looks like the instructions are taping off [disconnecting] the neutral and leaving it floating. In this instance you won't be able to draw power for anything but 220 volt loads from the gen head. Because the 110 volt loads are 'pulled' from the neutral and one or the other 'hot' terminals and both the neutral and two 'hot' wires from the gen head are fed to the duplex outlets, etc. So those instructions make no sense to me for the application being discussed but I may well be missing something. EXPY, thats just a bond they are removing, like the wire between the neutral and ground bus bars in an electrical pannel. Elsewhere the white should also be connected to the the center of the generator windings. Gotcha. You're saying that the neutral is connected elsewhere in the genny to the duplex outlets, etc, and the white wire in question is just part of the wiring to the other neutrals and it goes to ground [or may be disconnected]. You know, if I were going to connect a generator bigger than 9000 watts or so to both phases of a house via a 'permanent' xfer sw, I'd prolly run separate ground and neutral and unbond the neutral in the genny and connect both at the panel. I suppose that's what the 3 pole transfer sw is about? |
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Quoted:
So, when I get the generator, I'll dig into it a bit, and see how to disconnect the bond. But if I understand Country Boy, in a application like this, it is not critical that the neutral is floating? Stay Safe, Matt Edited to add: Thanks a lot, folks. I really appreciate all the advice and insight we help each other with here. Hopefully I can someday help somebody out! I think it depends. Bonding the neutral in the genny arguably adds another level of safety if, say, one of the wires comes loose in a plug or receptacle. When used when the genny isn't connected to a service entrance via a transfer sw. At least that's the way I analyze it. |
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Quoted:
Quoted:
I looks like the instructions are taping off [disconnecting] the neutral and leaving it floating. In this instance you won't be able to draw power for anything but 220 volt loads from the gen head. Because the 110 volt loads are 'pulled' from the neutral and one or the other 'hot' terminals and both the neutral and two 'hot' wires from the gen head are fed to the duplex outlets, etc. So those instructions make no sense to me for the application being discussed but I may well be missing something. EXPY, thats just a bond they are removing, like the wire between the neutral and ground bus bars in an electrical pannel. Elsewhere the white should also be connected to the the center of the generator windings. Supposidly (an electrician told me) you can pull a neutral from one of the 110 plugs to go from a 3 wire 220 receptical to a 4 wire. |
This is how I always understood it:
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