mthomas1 Posted February 7, 2010 Report Share Posted February 7, 2010 What is the rule for sizing a service drop and SECs serving multiple service disconnects? For example if three service disconnects, each with 100A OCPDs, are powered from a single service drop, does the drop and/or the conductors to meters require the capacity to supply 300A, or is there a rule that establishes a lower requirement based on the assumption that a 300A total draw is unlikely? (And , yeah, I know what they ought to do with this entire service, but I want to understand the concept... ) Thanks. Download Attachment: multiple_service_01.jpg 38.45 KB Download Attachment: multiple_service_02.jpg 35.56 KB Download Attachment: multiple_service_03.jpg 41.86 KB Link to comment Share on other sites More sharing options...
Marc Posted February 7, 2010 Report Share Posted February 7, 2010 The service should be sized to be adequate for all loads present, which means a load analysis needs to be completed. There are code passages which show how to do this calculation. Marc Link to comment Share on other sites More sharing options...
MTL_Inspet_Man Posted February 7, 2010 Report Share Posted February 7, 2010 my understanding is the sizing should be total load (L) plus 25% Therefore L x 1.25 That should be the minimum for safety. Someone correct me if I am wrong thx Link to comment Share on other sites More sharing options...
Mr. Electric Posted February 8, 2010 Report Share Posted February 8, 2010 There are requirements in the National Electrical Code to do a calculation for that service (NEC 220). There is a multiple family example in annex D4(a). Unfortunately there is no easy rule of thumb that I am aware of. The wire (and other components) need to be sized properly to handle the load of the property - not the breaker sizes. In other words it is very likely that a load calculation for a triplex would come up at 150 amps, even thought the main breakers for each unit are rated at 100 amps. If you think it is too small then I would recommend that you recommend that the owner or buyer hire a qualified electrical contractor to inspect it, and provide a proper load calculation for the property. By the way I agree - time for a service upgrade! Link to comment Share on other sites More sharing options...
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