Grounding Requirement For 100A Subpanel - Electrical - DIY Chatroom Home Improvement Forum

Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical


Thread Tools
Display Modes
Old 12-08-2010, 03:25 PM   #1
Join Date: Dec 2010
Posts: 4
Rewards Points: 10

Grounding requirement for 100A subpanel


I live in Michigan

I'm installing a 100A subpanel for a kitchen remodel fed off a 100A breaker in the main panel.

I understand that the ground and nuetral should NOT be bonded in the subpanel - only in the main panel.

I'm using #2 copper THHN cable to feed the subpanel (2 hots and one neutral)

I have a couple questions:

1) What size ground wire is required for a 100A subpanel (from main panel ground to subpanel ground)? I know #2 THHN is likely overkill for the ground and I'd like to save some money if it is safe to do so.

2) If I use uninsulated ground wire, will I have problems with corrosion against the rigid conduit, or is insulated ground cable preferred?

Any advice is appreciated

blakeasaurus is offline   Reply With Quote
Sponsored Links
Old 12-08-2010, 04:12 PM   #2
Master Electrician
Join Date: Mar 2010
Location: Indiana
Posts: 4,413
Rewards Points: 5,082

Your post indicates you are using metallic raceway between panels. This would suffice as your equipment grounding. Personally, I would add a #8 copper equipment grounding conductor, either bare or insulated.
brric is offline   Reply With Quote
Sponsored Links
Old 12-08-2010, 05:59 PM   #3
Electrical Supplier
Join Date: Jun 2010
Location: Dayton, OH
Posts: 205
Rewards Points: 150

How far away from the main panel is the subpanel?

To directly answer your downsizing question, you are allowed to down size your ground to 70% ampacity rating of the Current Carrying Conductor Rating (Hots) as long as it is larger than 10 AWG. Yes, #2 IS DEFINITELY OVERKILL

Assuming what I do know, if you use the metal conduit, THAT is your ground, however I would use grounding insulating bushings at both ends if you decide on this route. They are tied into your ground bar with a piece of bare copper at both ends.

I would avoid rigid metal conduit in residential rework, but thats me.

Also, you can get by with #3 THHN-2 for your Hots and Neutral. If you dont mind downsizing the panel to 90 amps, #4 will work for that.

From my understanding if you run any subpanel, it MUST have separate Ground and neutrals.....(Isolated)

I would go with 6 or 8 Insulated THHN if you decide to run a wire. (This is what I personally would do at my house..) In all honesty, the cost savings on a short run will be extremely negligible.

FYI If you are pulling a permit on this, get with your Inspector and check to see if he allows using Phase Tape on your wires or if you have to have a colored jacket.
"Do it right the first time and avoid duplication of effort"

Your AHJ/Inspectors ALWAYS have the final say on ANY electrical code issue.
If in doubt, contact a licensed, experienced, reputable electrician to perform the work.
LyonsElecSupply is offline   Reply With Quote
Sponsored Links

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Grounding a Subpanel Craigman Electrical 25 12-07-2009 07:25 PM
Adding second grounding bar to subpanel rdy2go Electrical 11 09-13-2009 07:59 PM
Subpanel grounding CAUTIOUSHOMEOWNER Electrical 30 12-02-2008 04:08 PM
Grounding electrode at subpanel Randell Tarin Electrical 18 02-01-2008 09:05 PM
Anyone want to take a shot at why #6 to attach antenna ground to breaker? Piedmont Electrical 44 01-08-2008 04:11 PM

Top of Page | View New Posts