Feeder Size

[mstrlucky74]

So have uinknown feeder size and unknown source feeding an exting 250A main breaker panel that is being relocated. We have to extend feeder to new panel location. Obviously have to know extg. feeder size so we can splice and extend but it can't be larger than 250A, correct?

 

[Jraef]

So have uinknown feeder size and unknown source feeding an exting 250A main breaker panel that is being relocated. We have to extend feeder to new panel location. Obviously have to know extg. feeder size so we can splice and extend but it can't be larger than 250A, correct?

CAN'T be? No, not true. The conductors could be sized for a larger feeder circuit, so long as the feeder breaker is appropriate for those conductors, because your panel has it's own main breaker. So for example you could have a 400A FCB and conductors sized for 400A, then someone put in that 250A MCB panel; it would be perfectly fine to have done that.

 

[infinity]

So have uinknown feeder size and unknown source feeding an exting 250A main breaker panel that is being relocated. We have to extend feeder to new panel location. Obviously have to know extg. feeder size so we can splice and extend but it can't be larger than 250A, correct?

IMO it's likely that the existing feeder is not larger than 250 amps but who knows. As Jraef stated it certainly can be since there are a large number of variables.

 

[mstrlucky74]

CAN'T be? No, not true. The conductors could be sized for a larger feeder circuit, so long as the feeder breaker is appropriate for those conductors, because your panel has it's own main breaker. So for example you could have a 400A FCB and conductors sized for 400A, then someone put in that 250A MCB panel; it would be perfectly fine to have done that.

Thanks. So the feeder conductors needs to be sized to the OCPD at the source?

 

[infinity]

Thanks. So the feeder conductors needs to be sized to the OCPD at the source?

Yes.

 

[Jraef]

Well, I'd put it the other way around. The feeder OCPD is there to protect the conductors. If you want to over size the conductors compared to the OCPD, you are welcome to. That happens quite a bit in large feeders where future expansion is planned in, i.e. you have a 1200A frame breaker and run 1000A rated conductors because you may need it some day and don't want to have to pull new conductors. So for now you are only using 800A therefore you use an 800A rating plug in the breaker and 5 years from now when you add something, you can simply change to a 1000A rating plug and away you go!

But I have a habit of over thinking things. Infinity is right, MOST of the time the conductors match the feeder OCPD because people don't like the price of copper.

 

[oldsparky52]

The drawings don't indicate the conductor size?