Cust. wants 200 to 400a upgrade to account for added load at new pole blg. Is it allowed to serve the pole blg. via 2nd set of lugs in 400a MB ? At 120 ft. from MB to blg., feeding 100a panel w/main, what calculation do I use for cable size ? Also what's best method to bond blg. skin ? Thanks, Dan.

Dan,

You say, he wants 200 to 400a upgrade, did you do the load calcs., to determine what he really needs?
If you need to ask about calculation for cable size, your most likely over your head with the job.

Sorry derater, I would have to go with LK on this. Cable size calcs are first year, if not first month, apprentice material. If you don't know, you should at least know where to look.

This job isn't replacing a bad light switch. Please hire a qualified professional. Nobody wants to see you hurt yourself or anybody else.

I've done dozens of upgrades, just none quite like this one. Main ? was using 2nd lug to go DIRECTLY to other blg. On cable size; yeah I can reference the table same as anyone; thought someone would know off the top of their head. Existing service is 200a. H/O added attached garage, 24 x 24 addition, heated swimming pool, hot tub, and lots of landscape lighting. Pole blg is for auto repair and restoration shop w/ welders, compressor and of course lights and receptacles. Did I do a load calc, on NEC embossed paper, no. Who here thinks upgrade unnecessary ?

"yeah I can reference the table same as anyone"

This job needs to be calculated, there is no table for it.

No one is saying the upgrade is not necessary, were just saying, you have to calculate, and layout the job, it's not a typical, single dwelling service upgrade.

In our utility area, on job like you described, we have to submit a load sheet to the utility before we can proceed.

Try to get all the information, on the existing loads, and the intended loads, for the pole barn. Use scrap paper, no needd for anything formal.

"Pole blg is for auto repair"

You will need to know all the loads for that building, not just I am using it for a repair shop. Get some figures and we can start working thru it.

Take a look at this link http://ecmweb.com/mag/electric_commercial_load_calculations/