Discussion in 'Electrical Forum discussion & Blog' started by Nate R, Aug 21, 2008.

1. Nate RNew Member

Joined:
Jan 11, 2007
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I perform R&D testiing at small engine manuf.
Location:
Milwaukee, WI
My house has a Square D Load center likely installed in the 70s. It's only a 12 space box, which is not enough for my needs. I have 100 amp service, and a residential load calculation based on the future setup of the house came in around 68 Amps, IIRC. So there's headroom. (Small 900 SF House, no Basement, gas range, gas dryer, gas water heater.)

Anyway, I want to add a subpanel so I can have the appropriate number of circuits.

So I have 2 questions as I try and figure out the feeder size for the subpanel.

How do I interpret this sticker? Does it mean ONLY Use 8-14 gauge wire, and ONLY solid? Or does it mean I can use larger than 8 gauge, but if it's 8 or smaller it must be solid wire?

If I am limited to 8 gauge, the ampacity of the feeder is limited to 40 amps unless then connections and wire are all rated for 75C instead of 60, correct?
If so, can I interpret this sticker to mean that the connections made in the box w/ CU wire are definitely rated for 75C, so I can run a 50 amp breaker instead of 40?

And, if I am indeed limited to 8 gauge on the neutral, does that limit me to 40 or 50 amps, or can I run 6 gauge Hots and an 8 gauge Neutral to the subpanel and get a 55 or 65 amp rating?

Just in the planning stage now, but trying to finalize plans. Can't do that until I know what load the subpanel can carry. Then I can figure out which circuit will go in which box.

I hope I've provided enough info. Thanks!

Joined:
Jun 16, 2007
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That means those small terminals can only accept 14-8 ga solid conductors.

#8NM is only good for 40A since it is limited to the 60 deg C column.

You can get an add-on neutral lug for that bar. Bring those pics to a real electrical supply house (must be a Sq D dealer) and they can sell you what you need to terminate a larger wire on that neutral bar.

4. Nate RNew Member

Joined:
Jan 11, 2007
Occupation:
I perform R&D testiing at small engine manuf.
Location:
Milwaukee, WI
Thanks for the Speedy Response!

BUT, I wasn't necessarily planning on using NM. If I pull individual wires through conduit, I should be able to get 75 deg rated stuff, correct? (Or can I not get 8 gauge solid wire because it would be such a PITA to work w/?) (It is only about a 8 foot run w/ one bend.)

Also, since this is a neutral, so does 8 gauge still limit me to 40A?

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That's different. You can use #8THHN up to 50A.
I would not derate the neutral for such a circuit. You can proabaly find #8 solid at a supply house.

6. Nate RNew Member

Joined:
Jan 11, 2007
Occupation:
I perform R&D testiing at small engine manuf.
Location:
Milwaukee, WI
Well, given that the box also doesn't have a bus bar, I think I may be going to an electrical supply house anyway to get one of those for this box. So I'll probably just get some sort of add on for the neutral bar then.

Any other opinions on this? Would anyone else also NOT derate the neutral on a subpanel feed? Or would you derate it?

The other lingering thought I have is this: I'm betting it's not, but any legality to running a 6 gauge wire that was wire nutted to 2 8 gauge wires for this situation? Certainly the hack way to do it, and I don't think I would unless I had no other option. But I am curious if that is specifically outlawed.

Although I dunno. The load calc right now is right at 31 or 32 amps for the subpanel, IIRC. So I could just run a 40 amp breaker. But it would leave a couple circuits open, so I'd rather run a 50 amp breaker if I could so that a circuit or 2 could still be added in the future w/o much hassle.

Last edited: Aug 21, 2008
7. Nate RNew Member

Joined:
Jan 11, 2007
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I perform R&D testiing at small engine manuf.
Location:
Milwaukee, WI
Hmm, if I follow the label, I HAVE to find some solid 8 AWG wire anyway. Whatever's easier. I'm starting to think that just getting some sort of add on to run 6 AWG stranded would be easier than finding and pulling solid 8 gauge.

8. jbfan74Electrical Contractor

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Jun 14, 2007
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Electrical Contractor
Location:
Newnan, GA
I never derate the netural for a sub. IMHO it does not save anything.
In fact, I have never derated a netural at all.

Joined:
Apr 2, 2008
You are the FIRST person to ever read those labels on a panel!

Ding! Ding! Ding! (Prize winner!)

Anyway, I assume that the picture above is of your main panel and that you would add a 100 amp breaker or less for the feed to your subpanel?

Notice in the picture above, there is also a wire size label on the first breaker and this label gives the wire sizes for *that* breaker's lugs...

Last edited: Aug 22, 2008
10. hjModerator & Master PlumberStaff Member

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Aug 31, 2004
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Plumber
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Cave Creek, Arizona
neutral

The only reason for derating a neutral is if a substantial portion of the load is 220/240 which does not require a neutral. In which case the neutral would only have to be sized for the maximum 115/120 load on one of the two legs. But for a small panel like this, the savings in wire size would probably not be enough to make it an issue.

11. Nate RNew Member

Joined:
Jan 11, 2007
Occupation:
I perform R&D testiing at small engine manuf.
Location:
Milwaukee, WI
I would only downgrade the neutral so I could use the existing bus.

Billy Bob: I don't get the point of your post. Yes, the main breaker lugs have wire size labels as well. Yes this is my main panel, and I'm pulling less than 100 amps off of it for a subpanel. I just don't see what you're getting at.

Joined:
Oct 20, 2005
Location:
New Hampshire
I had to put a larger neutral on a new Square D panel. I was running #2 to a subpanel.

I took a screw out of the neutral bar and took it to H D. I searched through their box of special fasteners and found one that matched the thread. I think it was 1/4-28. I got a capscrew about 1/2" long.Then I looked in the place where they have small uninsulated lugs in blister packs. I found one that handles #2.

I screwed that lug to the neutral terminal with the capscrew, and inserted the #2 cable into the lug and tightened the screw in the lug. You can do the same for the ground but you can use use a smaller ground. I'm away from my code but you can post another if you need the info.

The inspector saw it all and had no problem with it.

Don't try to find #8 or #6 solid. It will be a bear to pull.

You might be able to find Aluminum SE R cable that is rated for 75 C. If you have a long run it may be worth it. If you just have a couple of feet to an adjacent subpanel it isn't worth the trouble.

13. AlectricianDIY Senior Member

Joined:
Jun 15, 2007
Just use the stranded wire and a little common sense. It will be fine.

These lugs dont have the little flange thingy built in so technically, with just the screw head pushing on the wire there is a slight chance the strands will separate and not secure into the lug completely.

If you twist the strands together just a bit you will have a 100% connection.

14. MikeyAspiring Old Fart, EE, computer & networking geek

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Consumer
Location:
Central Florida
What does the Code have to say about tinning the end of a stranded wire to use it in a situation like this?

Joined:
Apr 2, 2008
I was just pointing out that the wire size you can use for the hots going to the subpanel would be labeled on the breaker you use for the hots going to the subpanel.

16. Nate RNew Member

Joined:
Jan 11, 2007
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I perform R&D testiing at small engine manuf.
Location:
Milwaukee, WI
Good thought, Mikey! I thought the same thing this morning, and was going to ask if there was any harm in tinning it.

17. AlectricianDIY Senior Member

Joined:
Jun 15, 2007
What would be the point in tinning them?

To keep the strands together?

Use your sidecutters and twist them together. You could have been done with this project by now

18. Norcal01New Member

Joined:
Aug 16, 2008

You can't use # 8 SOL anymore in conduit, see 310.3 2005 NEC