Return to the Electrical Wiring Forum | Post a Follow-Up

Silly ground buss connection question

Posted by daveho (My Page) on
Thu, Feb 4, 10 at 22:08

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.


Follow-Up Postings:

RE: Silly ground buss connection question

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

RE: Silly ground buss connection question

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.

more to add

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.

RE: Silly ground buss connection question

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

more again

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

RE: Silly ground buss connection question

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?



RE: Silly ground buss connection question

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

RE: Silly ground buss connection question

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

RE: Silly ground buss connection question

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

You'll only do it once.

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Electrical Wiring Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here