Adding loads to existing installations - where to evaluate?

[JNewquist]

This issue is about retrofits in commercial/industrial/municipal environments. NEC 220 is pretty clear about the method of determining existing loads (full info, utility for a year, 30 day demand) but my question is where am I required to do this calculation? It is clear that the code wants the loads evaluated at the panel being impacted. That's easy. Where else? Am I required to evaluate each distribution point upstream until I get to the service entrance?

This could easily become a question of best practices, potential liability, responsibility to Owner, poor design. But as this is the NEC thread, the question is what does the code require?

 

[d0nut]

The panel being impacted is not just the panel to which you are adding a breaker. Every upstream piece of distribution will also see that load and be impacted by the addition of the new load. Everything in the load path needs to be evaluated to make sure it will not be overloaded. The requirements of Article 220 would apply to everything in that load path.

 

[CutToTheChase]

My first thought is that the NEC doesn't explicitly specify where, just how to do load calcs (though don't bet anything of worth on this sentiment). Where in the code does it say you can't have 200A subpanel fed from a 100A breaker? As long as the feeder is sized appropriately I suppose, otherwise you run into 220.40.

Like d0nut says, everything upstream of the alteration will see the load change. It sucks and is usually painful to track down, but pays in the long run to ensure everything upstream is sized correctly.

 

[jap]

This issue is about retrofits in commercial/industrial/municipal environments. NEC 220 is pretty clear about the method of determining existing loads (full info, utility for a year, 30 day demand) but my question is where am I required to do this calculation? It is clear that the code wants the loads evaluated at the panel being impacted. That's easy. Where else? Am I required to evaluate each distribution point upstream until I get to the service entrance?

This could easily become a question of best practices, potential liability, responsibility to Owner, poor design. But as this is the NEC thread, the question is what does the code require?

The code requires electrical wiring to be installed in such a manner that if there happens to be an overload the wiring is suitably protected.

JAP>