120V Subpanel?

[jeff43222]

I got a guy who tells me his existing subpanel feeder cable is #6 with only three wires, and it's essentially wired up like a main panel, with a single ground/neutral bar.

Obviously, this is a violation, and he wants me to correct it so he can sell his house. His suggestion is to convert the subpanel to 120V, which the buyer is OK with. My question is whether it's legal to install a 120V subpanel. I've always installed 240V panels, but I'm not aware of anything in the code that actually requires subpanels to have two hots.

 

[davedottcom]

Re: 120V Subpanel?

No violation in having a 120 volt panel. You will still need to isolate the G's from the N's though!

Dave

 

[jeff43222]

Re: 120V Subpanel?

I perused Article 408 and didn't see anything prohibiting a 120V panel. I'll have to go look at the panel to see how feasible it is to install a separate ground bar; I may have to replace the subpanel (I have no idea how old it is, what kind, what shape it's in, etc.).

 

[Towzzer]

Re: 120V Subpanel?

Wondering if it's possible to jumper both the main lug so your not losing out on half the bus

 

[mdshunk]

Re: 120V Subpanel?

Originally posted by Towzzer:
Wondering if it's possible to jumper both the main lug so your not losing out on half the bus

Sure, but it probably doesn't have a lug that is rated for more than one conductor that you'd need to simply "jumper" the two. You'd have to use something like a split bolt or preinsulated pedestal lug and pigtail to both lugs. There should be enough gutter space to do so in all but the smallest panels.

 

[buck33k]

Re: 120V Subpanel?

I also wonder if the main lugs are rated for more than one conductor in the event of a jumper, and what about the aditional load now combined on only one #6.
Maybe its just as easy to pull in a new feeder.

 

[jeff43222]

Re: 120V Subpanel?

I'm going to go out and take a look at it this week, so I'll know more then what the job entails.

I'm not keen on the idea of jumpering the lugs to make two hots off of one wire. I'm sure if i did that, some future clown would put in a new circuit for his arc welder and wonder why it wasn't working right.

A new feeder would be a good idea, but I have no idea how it's fed now. The HO told me it's fed with a cable, leading me to think that it might be UF. I'm not going to be doing any trenching. If he's already got some conduit in place, then I'll suggest some new feeder wires.

 

[tshea]

Re: 120V Subpanel?

Don't forget about the multi-wire circuit aka shared neutrals.
May be cheaper to run a new feeder!

 

[roger]

Re: 120V Subpanel?

Originally posted by jeff43222:

The HO told me it's fed with a cable, leading me to think that it might be UF.

If this is a detached building there may not be any violation or problem at all.

250.32(B)(2)

Roger

[ September 11, 2005, 03:34 PM: Message edited by: roger ]

 

[jeff43222]

Re: 120V Subpanel?

Thanks, Roger. I took a look at the section, and I think the existing installation might be OK. I'm not sure if it's a detached building, but I'm assuming it is. I'll keep that section in mind when I go out on Wednesday and size up the situation.

250.32(A) seems to indicate that I may have to to pound in a ground rod (or two) at the garage. I'm guessing there's not one there now.

 

[roger]

Re: 120V Subpanel?

You're welcome Jeff, I hope this is the case.

Sorry about maybe having to drive a couple of ground rods though.

Roger

 

[jeff43222]

Re: 120V Subpanel?

I don't mind putting in a couple of ground rods. It's actually kinda fun with the rotary hammer, and it's much faster than when I used to use a sledgehammer.

It's much less fun in February, as I'm in Minnesota.

 

[davedottcom]

Re: 120V Subpanel?

I'm just gonna blurt this out with no research and very little thought put into it, so feel free to bash me all you want!

What about a 2-pole breaker with a jumper across both phases?
It would be like a split-buss panel back in the day...sort of!

 

[roger]

Re: 120V Subpanel?

Dave, there is nothing wrong (no bashing ) with that, but regardless of using one buss or two, we have to consider Tshea's post.

Roger

 

[mdshunk]

Re: 120V Subpanel?

I comes down to whether you want to do installs to code or do them with the stupidest person possible in mind.

True though, if there are no other metallic paths between the outbuilding and the house, there's no issue with leaving it connected like it is presently.

 

[davedottcom]

Re: 120V Subpanel?

Originally posted by mdshunk:
I comes down to whether you want to do installs to code or do them with the stupidest person possible in mind.

 

[roger]

Re: 120V Subpanel?

Originally posted by davedottcom:

Originally posted by mdshunk:
I comes down to whether you want to do installs to code or do them with the stupidest person possible in mind.

What does that mean?

Roger

 

[davedottcom]

Re: 120V Subpanel?

I have absolutely no idea, it just sounded funny when I read it!

 

[mdshunk]

Re: 120V Subpanel?

It was mentioned about someone installing a double pole breaker for a 240 load and it not working due to the panel only being 120. That's what I meant about choosing between code minimum or engineering for stupid people.

 

[George Stolz]

Re: 120V Subpanel?

Originally posted by davedottcom:
What about a 2-pole breaker with a jumper across both phases?

It would need to be secured as a backfed device, per (NEC-2002) 408.16(F).