First post here, I work on the industrial maintenance side as a plant electrician for a water treatment plant. Some of you may know me and this post from electriciantalk. 310.12 is tripping me up a little. I get that if a service/feeder is supplying the entire residential load then the wire can be downsized. Part (c) is tripping me up. The way I read it no feeder in a single dwelling needs to be bigger than 83 percent of the service rating. For example if you have a 200 amp service fed with 2/0 copper there is no need to use larger than 2/0 in any other feeders. That doesn't seem to be the consensus with more knowledgeable poeple. Can I gather some opinions on this.
Opinions on 2020 310.12(C)
- Thread starter mburtis
- Start date
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jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Yes, you have it correct. What else would it mean? And what reason could there be for a downstream feeder to be bigger than an upstream one (other than additional power sources on site) ?
Greentagger
Senior Member
- Location
- Texas
- Occupation
- Master Electrician, Electrical Inspector
Poorly written. Language focuses so much on entire load of the dwelling.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
You have it correct. This often occurs when you have a meter/main that has breaker spaces as well as feed through lugs to feed an inside panel.
Well I'm glad for that. I'm trying to help a buddy fix his sketchy garage panel so we can run a feed to his barn. Has a meter and 200 amp main breaker which originally feed the interior 200 amp panel via 2/0 copper. At some point they added a little exterior panel to run the garage and the ac but they just ran #4 copper over to the main breaker and stuffed it in on top of the 2/0. My plan is to replace the small exterior panel with a 200 amp feed thru, feed it with 2/0 from the main, then hook the 2/0 feeder to the interior panel up to the feed thru lugs.
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