I have an existing residential 200A. main lug panel already feeding some subpanels with a 100A. DP ckt. bkr, a 30A. Dp ckt. bkr, and some other DP utilization ckts. feeding electric ranges, etc. I'd like to add some more ckts. for an addition on the home and there are several remaining unused spaces on this panel. My question is, how do I determine the maximum amount of ckts and ampacity still available without overloading this panel, per the NEC? Or, should I take readings to determine the peak usage and base the available leftover on those?
Hey Russ, thanks for the reply. I thought of the load calculations also, but that would give me the allowable minumum load per the NEC. I want to make sure I'm not overloading the allowable peak usage of this existing panel, located in the basement. I should mention that it's a large, older home with at least two "lighting & branch-circuit" subpanels located on an upper floor and in the garage. There is also a heated inground pool on premise. BTW, wish it was my house...without the taxes of course.
True the code is minimum, and not always adequate, of coarse with out the calcs you don't even know what minimum is. Maybe if you draw up a list of the loads the owner will realize minimum is not enough.
It would make sense then to take the readings to find peak usage and use the NEC calculations to determine the load of the pool equip., central A/C, and the future addition. BTW, the house is in the Northeast, so I'll have to use the nameplate ratings and NEC calcs. to determine the loads for the pool and A/C equip.