Single CB Feeding Multiple Loads

[csully12]

I'm looking into a code compliance issue on a feeder installation and not sure if it meets code or not. The circuit is feed from a 3 phase 600 Amp CB in a switchboard (located outside) with the load side of the CB having 2-350kcmil's per phase. Each set of 350kcmil conductors goes into an underground conduit and lands in a down stream MLO panel (also outside) rated 400 Amps. Does this meet code? or should 2-300 Amp CB's be used in lieu of 1-600A.

 

[davidaengelhart]

I would say that the 400 amp MLO is overfused at 600 amps per NEC 408.36, and you can not parallel the overcurrent protection per NEC 240.8 ('08ED).

 

[RUWired]

Table 310.16 lists 350 kcmil cu. at 310 amps. If they are paralled two times, they are good for a 600 amps. The problem is the panel is a MLO only rated for 400 amps. Article 408.36 requires the panelboard to be protected at its rating.

 

[dcheser]

Check the circuit breaker and see if it has a rating plug. If it does you can change it to a 400-Amp plug. Breaker could also have adjustable trip settings in lieu of a rating plug that may allow you to adjust down. Worth looking into before you go to the expense of replacing the circuit breaker or making any other modifications.

 

[augie47]

The MLO is a violation either way, but just for clarification, do both sets of 350's land at one panel or does each set land at a separate panel.

 

[tkb]

I'm looking into a code compliance issue on a feeder installation and not sure if it meets code or not. The circuit is feed from a 3 phase 600 Amp CB in a switchboard (located outside) with the load side of the CB having 2-350kcmil's per phase. Each set of 350kcmil conductors goes into an underground conduit and lands in a down stream MLO panel (also outside) rated 400 Amps. Does this meet code? or should 2-300 Amp CB's be used in lieu of 1-600A.

Do you mean that both sets go to one 400 amp panel or each set going to different 400 amp panels?

 

[dcheser]

Augie47 why is the MLO considered a violation? From the original post I gathered both sets of 350's landed in the same equipment same MLO would this fall under 225.31 and 225.32 in the code book?

 

[augie47]

Augie47 why is the MLO considered a violation? From the original post I gathered both sets of 350's landed in the same equipment same MLO would this fall under 225.31 and 225.32 in the code book?

408.36

 

[Little Bill]

Each set of 350kcmil conductors goes into an underground conduit and lands in a down stream MLO panel (also outside) rated 400 Amps. Does this meet code? or should 2-300 Amp CB's be used in lieu of 1-600A.

The MLO is a violation either way, but just for clarification, do both sets of 350's land at one panel or does each set land at a separate panel.

Do you mean that both sets go to one 400 amp panel or each set going to different 400 amp panels?

Of course I'm not the OP, but from reading the above in red he says it lands in a down stream panel. That's how I see it.

 

[tkb]

Of course I'm not the OP, but from reading the above in red he says it lands in a down stream panel. That's how I see it.

Yes but the title of the thread says "Single CB Feeding Multiple Loads".

Why would he ask if 2-300 amp CB's should be used instead of 1-600 amp CB?

 

[defears]

If everything is outside you could say those 350's are taps(with a disconnect), and easiest solution would be get 2 300 amp main breaker kits for the 2 panels, and leave the 600 alone.

 

[Little Bill]

Yes but the title of the thread says "Single CB Feeding Multiple Loads".

Why would he ask if 2-300 amp CB's should be used instead of 1-600 amp CB?

Kind of a mixed message from the OP, and without hearing back from him IDK.
I took it to mean instead of doubling the wires from 1 600A breaker, he was asking if he should use 2 300A breakers to keep from doubling up on the 600A breaker. I don't think that would fly anyway. I may be wrong but I don't think you can run parallel feeders from 2 different breakers unless they were tied together, and I can't recall ever seeing two 3Ph breakers tied together.

 

[csully12]

Each set of 350's goes to an individual MLO panel. The question about 2-300 Amp CB's was top split the load at the 600 Amp CB and have the properly sized CB for the feeders.

 

[augie47]

Each set of 350's goes to an individual MLO panel. The question about 2-300 Amp CB's was top split the load at the 600 Amp CB and have the properly sized CB for the feeders.

Thank you for the clarification.
As far as the feeders, you possibly meet all the criteria for 240.21(B)(5) (outside taps), but the panels need to be protected per 408.36.
The way you (and the inspector) view 225.32-225.36 may dictate the "best" method, but, IMO, a properly sized MCB at the panels would be the best solution.**

**The location of the panels might well meet the NEC definition of a "structure" and Art 225.36 will apply