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coupe33 11-06-2009 09:09 PM

main panel distribution concern to out building
Hey guys I am building a new home and have a concern about the secondary feed to a detached building. have been given the what you should do by three different electricians and I am not saying any are wrong but looking for what is the best for long term. So here is my situation I have 250 mcm feeding my main lug breaker panel on the outside of home. it is a cutler hammer ch8b200rf. in short 200 amp main breaker with 8 slots on the buss bar with a 30 amp back feed breaker and an interlock kit. it only has single lug connections at the bottom of the buss bars. Thats great for feeding the house but now i need to get power to a 60x40 shop (personal use) at approx 175-200 feet away. My three suggestions were 1 add a splitter box to the side of my existing box and use the multiple lugs from it to supply power to what ever i want. 2 put bolt in lug bars of appropriate size inside current box and come off of them, this does the same as option 1 and eliminates the extra box on side of my home.3 use 125 amp breaker in current box come out of it with I believe #3 wich i was told is the largest wire that breaker will hold and run it to the building 200 feet away. the last option is the simplest because i am not adding or modifying anything. my concern was the distance with the wire size. I was told that based on the fact that my current shop runs on a 100 amp service with no problems that going to the 125 amp breaker and the distance will still work with no concern for over loading the wire,sinse i have a more than adequate wire size supply to the main breaker box i metioned above on the house. Any input- or are all three perfectly exceptable ways to accomplish what i want with out having a saftey issue.

J. V. 11-07-2009 10:54 AM

Option #3 is the only compliant method you describe. This feeder must be protected. It must be fed from a breaker or fuses. You should search this forum for "sub panels". It is by far the most asked question around here. There are a couple threads on this exact project in progress as we speak.

The distance to your structure is considerable. 200'. I would go with a 100 amp main breaker panel and #2 Cu wire. Use a 100 amp breaker in the main panel for the feeder.

kbsparky 11-07-2009 01:37 PM

The lugs on most 125 Amp breakers I've seen are rated for up to 2/0. Check the ratings on yours.

kbsparky 11-07-2009 01:45 PM


Originally Posted by J. V. (Post 350203)
Option #3 is the only compliant method you describe. This feeder must be protected. It must be fed from a breaker or fuses......

In this situation, one could invoke the tap conductor rules as outlined in section 240.21(B)(5). The conductors tapped from the sub-feed lugs in a feed-thru panel are protected by its 200 Amp main breaker.

This would be a compliant installation, even if they were substantially smaller than 200 Amp rated. Provided that they terminated into a properly sized and protected main breaker panel, and that was a given in this instance. :whistling2:

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