subpanel

[ravenjoe]

I have a 100 amp 30 pole 3 phase 4w main 208/120 lighting panel. This is an industrial application. Can I install a 3 phase 100 amp sub panel or should I go with a 60 amp. What is the code and article on this subject.

 

[dcl34769]

Re: subpanel

what is the current load on the existing panel?

what will the load be on the new panel and will the existing panel handle it?

 

[ravenjoe]

Re: subpanel

Unfortunately I can't verify the load because over many years incompetent electricians have added circuits without calculating the load and keeping the drawings and panel schedule updated. They have doubled up on 7 breakers and I don't know what they feed. The customer wants to get those doubled up circuits off the existing breakers and on their own dedicated circuit. I wanted to upgrade the panel but they can't take the entire panel off line because some of the circuits are for process control. But the panels main designation is lighting and receptacles. So I think a sub-panel is my best bet.

 

[hillbilly]

Re: subpanel

What size conductors are feeding the existing panel? Where do they come from and are they protected?

 

[ravenjoe]

Re: subpanel

The 30 KVA lighting transformer is fed with 440 3, phase #4 awg wire. The secondary feeds the panel with #2 awg.

 

[ravenjoe]

Re: subpanel

60 amp HMCP breaker feeds the transformer.

 

[mclain]

Re: subpanel

The 30KV transformer feeding the 100 amp panel is good for 83 amps at 208 (3 phase). If your are only adding a sub panel to move the seven circuits that are currently doubled up on the existing panel you are not increasing the load. But sooner or later someone will add additional breaker. The problem I see with the current installation is that the feeder breaker is to large. 30KV at 440 volt is 39.36 amps X 1.25% =49 amps. (450.3(B) Note 1) Next standard rated cb = 50 amps