Subpanel questions

Ogrebonz

NAXJA Forum User
I have a little snag in my wiring plans for my detached shop. Here's what I have in place:
  • 100 AMP Square D Home line panel in the shop
  • Direct bury rated four conductor cable, 1/0, 1/0, 1/0, 2 awg
  • 100 AMP breaker for the panel in the house, Square D QO (200amp)
Here are my issues:
  • The 100 amp QO breaker for the house panel is only rated for 2 awg wire
  • The house panel has neutral (white) and ground (bare and green) connected to the same bus bars, along with the bare cable coming in from the pole. There is no bus bar or ground wire anywhere else in this panel.
  • The shop panel has a separate bus bar for ground and neutral
And my questions:
  • Is there a way to use the 1/0 wire in the breaker rated for 2 awg?
  • Do I connect the neutral and the ground to the same bus bar in the house panel, the way everything else is?
  • Do I connect neutral and ground bus bars together in the shop panel?
  • Should I have a grounding bar (stake) for the shop panel?
Yeah, I know someone will tell me to call an electrician, and I may have to, but I'm not as dumb as my questions might make me out to be.

I did the load calculations and figured in the distance from the house and worked it out with the wife's uncle, who is a retired lineman. I'd ask him for more help, but he moved to Arizona!
 
And my questions:
  • Is there a way to use the 1/0 wire in the breaker rated for 2 awg?
  • Do I connect the neutral and the ground to the same bus bar in the house panel, the way everything else is?
  • Do I connect neutral and ground bus bars together in the shop panel?
  • Should I have a grounding bar (stake) for the shop panel?

- Doubt it. Are you using Aluminum or copper? If copper, then #2 should be fine - http://www.doityourself.com/forum/electrical-c-d-c/447348-what-wire-100amp-subpanel.html#b
- Yes, if there are no other options.
- No, they should be separate as far as possible.
- Yes
 
Neutrals and grounds can run off of the same bar. A neutral is a ground with a potential load. Use # 2. Yes but you don't have to if you have a ground bar off of the main panel coming from your house. But over kill isn't never a bad thing.
 
I already buried the four conductor cable, 1/0, 1/0, 1/0, 2 awg.

Thanks for the answers though, I may have power out there one of these days!
 
You probably have URD cable (Underground Residential Distribution). It's very common direct bury cable. The 4 conductors are spiraled together without an outer jacket, right?

First off, how far away is the shop? The longer the run, the more concern for voltage drop.

The grounds and neutrals are bonded together at the main panel only(whites & bare/green conductors) Today's standards require them to be on separate buss bars. Although is was okay a few years ago to land them on either and most inspectors will grandfather existing panels. SO the bare conductor coming from the pole should be attached to a ground rod somewhere along the way, maybe near the meter. Inside your main panel this conductor should land on the ground bus and have a means to bond to the other buss for the neutrals.(Main bonding jumper) This is usually a big green screw or some sort of a strap.

Any panel 'downstream' from the main panel needs to have the grounds and neutrals separated, so in your shop keep the whites on one buss bar and the bare/greens on the other and remove the MBJ (Large green screw or strap)

You have a couple of options for attaching the 1/0 to the 100A breaker at the house for the feeder. The QO line is pretty common, so I would try to swap breakers, that would be the easiest and result in the best installation. Probably the existing is only rated for copper (#2AWG THHN is good for 130 amps or so) The Aluminum is not as good a conductor so to carry 100A it needs to be larger. So find a 100a breaker rated for AL/CU and it should have large enough lugs to fit the 1/0 AL.

The other option is to install a junction box next to the panel and splice on #2 copper to each 1/0 al and go into the panel from there. That's more work, more parts and pieces and more chance for failure. If you do this, make sure you use split bolts rated for AL/ CU

Also on any of the aluminum use knolox or some similar anti-oxidant compound. Just a light coat will do.

Lastly, on any connections/terminations tighten them, then wiggle the conductors around and re-tighten. Aluminum is notorious for oxidizing and loosening over time.

Good luck!
 
Not sure if you mean coming to the house, which is overhead, or what I buried, which is direct bury, no conduit. Yes, twisted together with no jacket.

It's about 45', but I had to trench around my well, so the cable is about 65'.

I dug the trench and buried the wires last fall, but I seem to remember finding the ground stake for the house, I'll double check. There is no separate ground bus bar in the house panel, green, bare and white all are connected to the same bus bar.

I did use separate bus bars in the shop.

I must have gotten the right breaker, because my 1/0 cable will fit it just fine.

Didn't know about knoxlox, I'll be picking some up and re-tightening all conductors.

I have just a few more runs to the outlets to make and then I'll be hooking up to the main panel.

I certainly appreciate the advice.
 
Sure thing. That distance is fine and so is the ground buss at the house panel. Glad the breaker fit. Ive seen so many termination s over the years where it didnt so they cut strands off until it did. Not a good idea. Sounds like you have it well under control.

EDIT:

A couple of things I forgot to mention. Make sure the shop panel buss bars are not bonded together. If you have a meter, just check continuity between the 2 bars. If there is, remove the screw or strap to the back of the panel.
Also, at some point I'd try to find out if there were an specific requirements from what we call the AHJ (Authority having Jurisdiction) This could be a State inspector, bldg inspector a municipal authority, etc. Some areas in Maine have State inspectors and then City and some of the requirements will differ.

Check out the Michigan licensing board, too. You might find something there.

It sounds like everything is fine, so this isn't to worry you, I've just seen different grounding requirements in certain areas, regardless of what the NEC says. You have to consider that some soil/earth conditions vary and they may want you to have another rod tied into the existing, for example.

I'd just check around and ask a few questions here and there if you know some electricians in your area that would be good.
 
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Another question: My Lincoln welder has a 50amp tag on it. I have a 50 amp breaker for the panel (220v), but I haven't bought the wire yet. Eventually I'll buy a wire feed to replace the stick welder with, so I would like the outlet to work for either one. It has a three prong plug on it.

Should I switch the cord on the welder to a four wire and connect the ground to the case?
If so, what plug should I use?
It's about 40 feet from the panel to the plug, is 8-3 ok, or do I need 6-3?

Thanks for the help!
 
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