[ARCHIVED THREAD] - Question for electricians... (Page 1 of 2)
Posted: 1/24/2016 10:16:09 PM EDT
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I've had an interesting discussion on another forum regarding 3 vs 4-wire power feeds, and thought I would ask here as well.
I recently built a second shop, which is a completely separate structure not connected to any other buildings on the property. I've run a 100 amp subpanel in the shop with its own grounding rod, and just finished digging the trench and running close to 125-150' of underground 3-wire aluminum power wire. The first snag I ran into was the wire I bought ended up literally 10-12' too short...so I picked up an underground splice kit from a buddy who works for the local power company. My plan was to run plastic conduit from the panel to a point past the splice kit, and then seal the conduit to ensure no water intrusion. Well, in the process of discussing underground splice kits, it was pointed out that code no longer allows for 3-wire power feeds, and that all separate structures must now use 4 wires to feed the panel. Here are my questions. What is the risk of using a 3-wire feed versus that of a 4-wire (other than not meeting current code)? The shop is not attached to any other buildings, does not have any metal pipe or conduit, and the only thing "conductive" is the wiring and receptacles itself. Its my understanding that 3-wire was allowable by code until 2008, what precipitated the change? Will using a 3-wire power feed really kill the bus load of nuns I have parked in the shop?? 
Thanks! |
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There are tens of thousands - or more, 3 wire feeds that are grandfathered in before they changed the code. If you have no code inspector and you've wired it all up properly then no biggie.
You're going to have to pump a full tube of silicone sealent in the end of that buried conduit - that part worries me more than 3 vs 4 wire. **not an electrician** |
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I believe they want all grounds to terminate at a common point (at the main), so that is why they want the 4 wire setup. That is what I was thinking. For whatever reason a separate ground rod at the other location may not be ideal. I do not understand what might be happening in that case. Does the repair kit include some sort of heat shrink to cover the splice? I would imagine...not being an electrician...that you want that splice to be electrically sound and resistant to water entry. |
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That is what I was thinking. For whatever reason a separate ground rod at the other location may not be ideal. I do not understand what might be happening in that case. Does the repair kit include some sort of heat shrink to cover the splice? I would imagine...not being an electrician...that you want that splice to be electrically sound and resistant to water entry. Quoted:
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I believe they want all grounds to terminate at a common point (at the main), so that is why they want the 4 wire setup. That is what I was thinking. For whatever reason a separate ground rod at the other location may not be ideal. I do not understand what might be happening in that case. Does the repair kit include some sort of heat shrink to cover the splice? I would imagine...not being an electrician...that you want that splice to be electrically sound and resistant to water entry. When you use separate grounding rods at different panels on your property without a way to tie them together, then you have a real possibility of grounds at different potentials with respect to one another. Also, the UG splice kits we use on the railroad come with molds and epoxy sealer to make them waterproof. Your splice kit should have a 2 part mold that snaps over the splice and a two part epoxy to fill it with. ETA, IIRC, 3M makes the splice kits we use. I'm sure they're a common type used anywhere and underground splice needs to be made. |
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Unless there in no inspection then run with it No, there will be no inspection. Does the repair kit include some sort of heat shrink to cover the splice? I would imagine...not being an electrician...that you want that splice to be electrically sound and resistant to water entry. Yes. The kit has three large butt connectors (not sure of the correct term), and each connector has two badass pieces of heat shrink tubing. My buddy tells me that once its in place, you damn near can't remove it with a knife. I'd be more concerned about the splice being right. The splice is what concerns me the most as well, I don't want to screw it up. The good thing about the location, though, is the splice point is covered by another barn..although water intrusion is still a risk. Any suggestions on what type of sealant to use on the conduit? |
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I believe they want all grounds to terminate at a common point (at the main), so that is why they want the 4 wire setup. This is part of it. They have really gone out of their way to require supplemental grounding. Gone are the days of just sinking a ground rod at your residential service. Now you have to install a ufer ground if you can, a cold water pipe ground aas well as a ground rod. |
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One simply does not question the code panel one just accepts it. They are God like or so they think. Indeed. Even if what they tell you is something that some old guy without any education pulled out of the air, with no regard to code. They have the keys to the kingdom, you do what they say. |
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so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Yes. Because the neutral is a current carrying conductor and the ground conductor is supposed to be a safety feature, they want all grounds and neutrals away from the main panel to be separate. |
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I was once warned when I thought about doing some electrical work without a permit that if there was a fire and insurance company caught wind of it they may deny the claim. I was never willing to take the chance after that.
I now work for the electric utility and warn people all the time that they should be very familiar with the current NEC rules or have a talk with the inspector. I'm always amazed how many people start doing work before knowing what is the right and wrong way to do something. Been a few times they have to start the project completely over. I'm also a big fan of dealing with retired electricians...."back when I was working this is how we did things, what do you mean I can't do that?".  Many hours wasted arguing about why they can't do things the old way.
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I was once warned when I thought about doing some electrical work without a permit that if there was a fire and insurance company caught wind of it they may deny the claim. I was never willing to take the chance after that. I can see that being a potential issue, but only if the fire was started due to an electrical fault within the building. |
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so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Wat? Also, OP save yourself the trouble of doing whatever it was you were going to do with the conduit. If you used a legit underground splice kit at this point just go with it. I don't care how good you seal the PVC it will end up filled with water. I probably would have brought the wires straight to the surface and functioned them in an approved ground box ( they're cheap and you can drive over them) I did a job once where the customer head an outbuilding about 200 feet out. I had them run a separate 2" conduit for my camera wires. Their "electrician" ran 3 wire direct bury. Not only that but he asked if I was going to stay and put my wires in the pipe as I ran it
This tard laid out the wire and slid the conduit over it piece by piece for 200' 
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Quoted: Wat? Also, OP save yourself the trouble of doing whatever it was you were going to do with the conduit. If you used a legit underground splice kit at this point just go with it. I don't care how good you seal the PVC it will end up filled with water. I probably would have brought the wires straight to the surface and functioned them in an approved ground box ( they're cheap and you can drive over them) Quoted: Quoted: so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Wat? Also, OP save yourself the trouble of doing whatever it was you were going to do with the conduit. If you used a legit underground splice kit at this point just go with it. I don't care how good you seal the PVC it will end up filled with water. I probably would have brought the wires straight to the surface and functioned them in an approved ground box ( they're cheap and you can drive over them) what part did i lose ya? 4 wire.. 2 hot, N, G.. n and g bond to the main panel and sub panel. AND a continuous ground rod from the sub (double ground rod looped with #8 copper) seems redundant to the redundant.. but another poster refreshed my memory.. its been a minute |
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Yes. Because the neutral is a current carrying conductor and the ground conductor is supposed to be a safety feature, they want all grounds and neutrals away from the main panel to be separate. Quoted:
Quoted:
so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Yes. Because the neutral is a current carrying conductor and the ground conductor is supposed to be a safety feature, they want all grounds and neutrals away from the main panel to be separate. If that's the case his 3 wires in the hole is good, right? Then just connects his bare grounds to the rod at the structure keeping them separate from neutral. |
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Also, OP save yourself the trouble of doing whatever it was you were going to do with the conduit. If you used a legit underground splice kit at this point just go with it. I don't care how good you seal the PVC it will end up filled with water. I'm kind of shooting for double redundancy here....but how will the conduit fill with water if its sealed? |
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what part did i lose ya? 4 wire.. 2 hot, N, G.. n and g bond to the main panel and sub panel. AND a continuous ground rod from the sub (double ground rod looped with #8 copper) seems redundant to the redundant.. but another poster refreshed my memory.. its been a minute Quoted:
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so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Wat? Also, OP save yourself the trouble of doing whatever it was you were going to do with the conduit. If you used a legit underground splice kit at this point just go with it. I don't care how good you seal the PVC it will end up filled with water. I probably would have brought the wires straight to the surface and functioned them in an approved ground box ( they're cheap and you can drive over them) what part did i lose ya? 4 wire.. 2 hot, N, G.. n and g bond to the main panel and sub panel. AND a continuous ground rod from the sub (double ground rod looped with #8 copper) seems redundant to the redundant.. but another poster refreshed my memory.. its been a minute Lol That's not how this works. That's not how any of this works It's simply a 4th wire that runs from the main panel ground bar to the sub panel ground bar. No other ground rods, especially "looping ground rods" whatever that is. NEC is #6 to the ground rod assuming you have a separate water ground sized appropriately but none of that applies here anyway. Bond to the main panel and sub panel? No idea what that's supposed to mean |
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I'm kind of shooting for double redundancy here....but how will the conduit fill with water if its sealed? Quoted:
Also, OP save yourself the trouble of doing whatever it was you were going to do with the conduit. If you used a legit underground splice kit at this point just go with it. I don't care how good you seal the PVC it will end up filled with water. I'm kind of shooting for double redundancy here....but how will the conduit fill with water if its sealed? I'm not exactly sure but it does. I've always assumed it had something to do with the moisture in the trapped air condensing. Most times when a conduit has already been in the ground for awhile I would use the vacuum to draw a foam plug through to get the water out before sucking in the pull line |
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I can see that being a potential issue, but only if the fire was started due to an electrical fault within the building. I totally agree with you. I am really just a big chickenshit that never takes chances. My life is very "vanilla". 
Like someone said before, if you are going to direct bury your wire, then make sure the splices are completely water tight. I personally would install conduit for the run because it's relatively cheap and digging up conductor and chasing bad splices or other issues is a pain in the ass. |
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Like someone said before, if you are going to direct bury your wire, then make sure the splices are completely water tight. I personally would install conduit for the run because it's relatively cheap and digging up conductor and chasing bad splices or other issues is a pain in the ass. If I could go back, I probably would have used conduit the full length. Unfortunately, 95% of the trench has been covered and packed now (part of it went through the driveway), with the "splice section" the only part still uncovered. |
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If that's the case his 3 wires in the hole is good, right? Then just connects his bare grounds to the rod at the structure keeping them separate from neutral. Quoted:
Quoted:
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so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Yes. Because the neutral is a current carrying conductor and the ground conductor is supposed to be a safety feature, they want all grounds and neutrals away from the main panel to be separate. If that's the case his 3 wires in the hole is good, right? Then just connects his bare grounds to the rod at the structure keeping them separate from neutral. Its good to keep ground and neautrals separated (except where they bond at the main). However, as I mentioned before, if the grounds do not all share a common termination point, they can be at different potentials with respect to one another. IOW, this ground may be a few volts different than that ground. |
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If I could go back, I probably would have used conduit the full length. Unfortunately, 95% of the trench has been covered and packed now (part of it went through the driveway), with the "splice section" the only part still uncovered. Quoted:
Like someone said before, if you are going to direct bury your wire, then make sure the splices are completely water tight. I personally would install conduit for the run because it's relatively cheap and digging up conductor and chasing bad splices or other issues is a pain in the ass. If I could go back, I probably would have used conduit the full length. Unfortunately, 95% of the trench has been covered and packed now (part of it went through the driveway), with the "splice section" the only part still uncovered. Unless you have really rocky soil or you're planning on paving over it using direct bury wire is fine. (Unless you cut it short  )
Next time just 90 the wire up to the surface and use a quazite box or similar to junction Eta: I see it goes through your driveway. I wouldn't necessarily have piped it the whole way but I would at least put a sleeve in the width of the driveway |
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Its good to keep ground and neautrals separated (except where they bond at the main). However, as I mentioned before, if the grounds do not all share a common termination point, they can be at different potentials with respect to one another. IOW, this ground may be a few volts different than that ground. Quoted:
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so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Yes. Because the neutral is a current carrying conductor and the ground conductor is supposed to be a safety feature, they want all grounds and neutrals away from the main panel to be separate. If that's the case his 3 wires in the hole is good, right? Then just connects his bare grounds to the rod at the structure keeping them separate from neutral. Its good to keep ground and neautrals separated (except where they bond at the main). However, as I mentioned before, if the grounds do not all share a common termination point, they can be at different potentials with respect to one another. IOW, this ground may be a few volts different than that ground. Basically the issue with using 3 wire is if your ground rod at your outbuilding is a better path to ground then instead of going to the ground at the main service everything could flow across your new neutral and out to the new ground. I'd ditch the new ground rod and bond the ground bar in the sub panel |
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If I could go back, I probably would have used conduit the full length. Unfortunately, 95% of the trench has been covered and packed now (part of it went through the driveway), with the "splice section" the only part still uncovered. Quoted:
Like someone said before, if you are going to direct bury your wire, then make sure the splices are completely water tight. I personally would install conduit for the run because it's relatively cheap and digging up conductor and chasing bad splices or other issues is a pain in the ass. If I could go back, I probably would have used conduit the full length. Unfortunately, 95% of the trench has been covered and packed now (part of it went through the driveway), with the "splice section" the only part still uncovered. I must have missed that part, sorry. In that case I would bring it up into a flush mount splice box if that is an option. Either that or measure out where the splices are and/or the end of the conduit is for future repairs if needed. Congratulations on the new shop by the way, a guy can never have too much shop space! |
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Basically the issue with using 3 wire is if your ground rod at your outbuilding is a better path to ground then instead of going to the ground at the main service everything could flow across your new neutral and out to the new ground. Quoted:
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so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Yes. Because the neutral is a current carrying conductor and the ground conductor is supposed to be a safety feature, they want all grounds and neutrals away from the main panel to be separate. If that's the case his 3 wires in the hole is good, right? Then just connects his bare grounds to the rod at the structure keeping them separate from neutral. Its good to keep ground and neautrals separated (except where they bond at the main). However, as I mentioned before, if the grounds do not all share a common termination point, they can be at different potentials with respect to one another. IOW, this ground may be a few volts different than that ground. Basically the issue with using 3 wire is if your ground rod at your outbuilding is a better path to ground then instead of going to the ground at the main service everything could flow across your new neutral and out to the new ground. Yes. The current coming into your service from the transformer wants nothing more than to return to that transformer. Ideally, leg to leg, or leg to neutral is the way that happens. The ground is just an alternate path. 
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Basically the issue with using 3 wire is if your ground rod at your outbuilding is a better path to ground then instead of going to the ground at the main service everything could flow across your new neutral and out to the new ground. What would cause this? I must have missed that part, sorry. In that case I would bring it up into a flush mount splice box if that is an option. Either that or measure out where the splices are and/or the end of the conduit is for future repairs if needed. Being that it is very close to the panel itself, it won't be a problem locating the splice junction. |
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Quoted: I'm kind of shooting for double redundancy here....but how will the conduit fill with water if its sealed? Quoted: Also, OP save yourself the trouble of doing whatever it was you were going to do with the conduit. If you used a legit underground splice kit at this point just go with it. I don't care how good you seal the PVC it will end up filled with water. I'm kind of shooting for double redundancy here....but how will the conduit fill with water if its sealed? |
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Quoted: Lol That's not how this works. That's not how any of this works It's simply a 4th wire that runs from the main panel ground bar to the sub panel ground bar. No other ground rods, especially "looping ground rods" whatever that is. NEC is #6 to the ground rod assuming you have a separate water ground sized appropriately but none of that applies here anyway. Bond to the main panel and sub panel? No idea what that's supposed to mean Quoted: Quoted: Quoted: Quoted: so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Wat? Also, OP save yourself the trouble of doing whatever it was you were going to do with the conduit. If you used a legit underground splice kit at this point just go with it. I don't care how good you seal the PVC it will end up filled with water. I probably would have brought the wires straight to the surface and functioned them in an approved ground box ( they're cheap and you can drive over them) what part did i lose ya? 4 wire.. 2 hot, N, G.. n and g bond to the main panel and sub panel. AND a continuous ground rod from the sub (double ground rod looped with #8 copper) seems redundant to the redundant.. but another poster refreshed my memory.. its been a minute Lol That's not how this works. That's not how any of this works It's simply a 4th wire that runs from the main panel ground bar to the sub panel ground bar. No other ground rods, especially "looping ground rods" whatever that is. NEC is #6 to the ground rod assuming you have a separate water ground sized appropriately but none of that applies here anyway. Bond to the main panel and sub panel? No idea what that's supposed to mean thats where i got confused.. the 4th wire bonds the grounds between the two panels ... |
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Quoted: what part did i lose ya? 4 wire.. 2 hot, N, G.. n and g bond to the main panel and sub panel. AND a continuous ground rod from the sub (double ground rod looped with #8 copper) seems redundant to the redundant.. but another poster refreshed my memory.. its been a minute Quoted: Quoted: Quoted: so the NEC wants the sub panel double bonded to the main AND ran a separate continuous ground ? Wat? Also, OP save yourself the trouble of doing whatever it was you were going to do with the conduit. If you used a legit underground splice kit at this point just go with it. I don't care how good you seal the PVC it will end up filled with water. I probably would have brought the wires straight to the surface and functioned them in an approved ground box ( they're cheap and you can drive over them) what part did i lose ya? 4 wire.. 2 hot, N, G.. n and g bond to the main panel and sub panel. AND a continuous ground rod from the sub (double ground rod looped with #8 copper) seems redundant to the redundant.. but another poster refreshed my memory.. its been a minute So basically OP, if you're dead set on using 3 wire feeder, you HAVE to bond the neutral-ground at the sub-panel. If you don't, if you have a ground fault in the detached structure the breaker may not trip, even if you have a ground rod installed(which you will need-and if you have no supplemental ground, I believe you'll need 2 rods unless it's amended locally) Just know that while this WILL work just fine, it will not be a code compliant install. You could say you wired it all up in 2005 or some shit when this would have been legal. |
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Ok, had this suggested to me...
If it were me, in the shop panel I would pull the bonding screw on the neutral bar, and drive 2 ground rods and ground your panel. Just be sure to pull the bonding screw to isolate the neutral. I think the chances of creating a ground loop would be slim to none. |
| While we're on the subject, I've heard about well pumps leaking current to ground. Evidentiantly, this can set up a voltage gradient that can adversely effect livestock. Seems there was another thread today that mentioned something about overhead transmission lines and possible negative effects on livestock. |
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I'm kind of shooting for double redundancy here....but how will the conduit fill with water if its sealed? all underground conduit fills with water. you can make NASA-spec solvent-welded (aka glued) joints but the conduit will still fill with water. the reason is condensation. the ground temperature at conduit burial depth (typ. 18") is quite cool; and, the ends of electrical conduit are almost never sealed against infiltration. warm humid air enters the conduit, cools, and the moisture precipitates out. ask any electrician, he'll tell you... a year after you put conduit in the ground, it's pretty wet in the pipe. for this reason, underground raceway (conduit) is classed as a wet location, and by code you need to use appropriately rated methods and materials etc (e.g. THWN insulated wire; the "W" = wet location rated). ar-jedi |
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I agree with the grounding issue. Should all be bonded back to one ground at the service. Eta: if he bonded N-G would that affect GFI receptacles or those new breakers they're requiring? Doubtful if neutral/ground bond would affect those. They only care if the current leaving is equal (or within a couple mA) of the current returning. |
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Quoted: Ok, had this suggested to me... Quoted: Ok, had this suggested to me... If it were me, in the shop panel I would pull the bonding screw on the neutral bar, and drive 2 ground rods and ground your panel. Just be sure to pull the bonding screw to isolate the neutral. I think the chances of creating a ground loop would be slim to none. Here are the two options. The first is not currently code compliant but will work just fine. The second is what is now required by code. 3 wire feeder- ground/neutral HAS to be bonded together. Otherwise breakers don't trip(in a ground fault situation)- ground rod is required 4 wire feeder- ground/neutral HAS to be kept separate in the sub panel, otherwise current will flow through the grounding conductor and whatever it is attached to back to the main panel. - ground rod is required. Also, in your situation w/ 3 wire feeder- if you have a metal water pipe at the detached structure you do not bond to it. With a 4 wire system you would bond to it, because you won't be creating a parallel return path. Edit- and listen to ar-jedi- it doesn't matter what you do, that PVC will fill up with water. |
