Silly ground buss connection question

davehoFebruary 4, 2010

I'm putting in a 100A subpanel. The subpanel ground buss lug where the ground to the main panel is intended to be connected is rated for #4 or larger. #8 is all that is required for a 100A subpanel feed. #8 will fit into the other holes on the ground bar. Can I connect it to one of the smaller holes or do I need to use some kind of adpater to connect it to the intended lug?

I realize electrically it makes no difference, I just want to do it the right way. The panel is a Siemens G1624L1125CP if it makes a difference.

-Dave

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spencer_electrician

Don't have to use the lug, just use any screw on the ground bar.

    Bookmark   February 5, 2010 at 12:02AM
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sparky17

Also you have to remember that even tho you are putting in a 100 amp sub,you can only feed that sub with a 40A 2 pole breaker,from your "main panel"As the #8 gauge wire that your running to your sub is only rated for 45A.

Ive seen people feed 100A subs with 100A breakers just "cause thats what the panel was rated for"
This is wrong,the gauge of wire run to the sub determines how many amps your sub will have available.
You then need to feed it with the highest possible breaker without exceeding the ampacity of that said feeder wire,which in your case is #8.
#8 is good for 45 A therefore the max breaker you can use is a 40A 2 pole.
Hope this helps.

    Bookmark   February 6, 2010 at 9:09AM
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sparky17

One last thing,I've also seen this countless times on home wiring jobs on sub panels.
You have to physically disconnect the "neutral bar from the frame of the sub and or the ground bus"the neutral can only be touching ground in the main distribution panel,that would be the one in your house.
So when done you with have (2) hots, red and black, tied to your main lugs in sub,or right to your new "main breaker in sub"
(1) white neutral to the neutral bus (that is in contact with nothing else)
(1) bare ground tied thru the lug on your ground bushing (if you have used one in your sub)and then to the subs ground bus.

    Bookmark   February 6, 2010 at 9:31AM
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normel

Sparky17, I believe the OP is referring only to the grounding wire when he mentions #8, not the feed wires.

    Bookmark   February 6, 2010 at 9:42AM
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sparky17

Yea i thought of that when i replied,just trying to help.
Should have asked for more info i guess before offering my answer.

    Bookmark   February 6, 2010 at 9:53AM
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daveho

Thanks for the tips. Cu #8 THHN will be for the ground only. I'll be using Cu #2 THHN for the hots, & Cu #4 THHN for the neutral. I know not to bond the neutral & ground in the sub.

One more silly question. What's the easist way to strip the insulation off the large THHN. For smaller stuff, I usually use a rotary stripper designed for co-ax. Works good for #8 & smaller, but the #4 & #2 won't fit. I see they make a large gauge rotary stripper, but the tool is $35+ & I'd rather not spend that much for a couple of wires. Use a sharp razor blade I'm guessing?

Thanks.

-Dave

    Bookmark   February 8, 2010 at 10:01AM
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sparky17

Some guys use utility knives,like the ones you would cut linoleum with,i like to use a cheap yellow handled "bannana knife".

    Bookmark   February 8, 2010 at 11:11AM
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mike_kaiser_gw

You can use any sharp knife to strip the insulation but you should hold the knife on an angle to avoid nicking the wire.

    Bookmark   February 8, 2010 at 11:52AM
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pharkus

Want a challenge? Strip some #2 with fingernail clippers. One little "nip" at a time.

You'll only do it once.

    Bookmark   February 16, 2010 at 7:29PM
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