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|12-08-2010, 03:25 PM||#1|
Join Date: Dec 2010
Posts: 4Rewards 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
|12-08-2010, 04:12 PM||#2|
Join Date: Mar 2010
Posts: 3,781Rewards Points: 3,818
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.
|12-08-2010, 05:59 PM||#3|
Join Date: Jun 2010
Location: Dayton, OH
Posts: 205Rewards 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.
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