I was asked to look at a project the other day. The job is an 8 office strip. The owner has old equipment that is out of date and really beat up. He has a 4" conduit coming off the XFMR to a 8x8 gutter, out of the bottom of the gutter there is (8) meter cans, out of the bottom of the meter cans feeds (8) 100A diconnects. Out of the disconnects feeds (8) 100A distribution panels. The gutter has (3) 500mcm inside of it that has been sliced into for each meter base. The owner would like to install a new main disconnect, and replace the old worn out equipment. My question is If I install a new Main Disconnect the way I understand it, that it needs to be an 800Amp to protect the 8-100 panels? right.

Good evening and welcome to ECN

Firstoff, if you have 1-4" conduit, you probably have a 400 amp service feeder. To determine the service capacity, you need to know the AWG of the conductors, and the insulation.

The service capacity (amperage) is based on the load, not on the sum of the disconnects.

BTW, the "existing" service is illegal if you in fact have 8 disco's.

John

Yes I do realize that the existing service is "illegal" to todays standards, Please realize that this service about 25-30 yrs old. Yes I do belive that there is a 400 amp service, due to the fact that they fed it with 500mcm thhn. There is only 1 office that I belive pulls anything close to 100 amps and it is a pizzaria. All the other offices , even though I have not done a amparage reading, does not pull but 50 -55 amps each if that. Thank you for all your help.