Adjustable Trip breaker

[j2020]

Can someone please educate me on a question that I have. There is an existing Distribution Panel that is rated at 400A, 480V, 3 phase, 3 wire with 400A main breaker. I wanted to re-route an existing feeder from another existing Distribution Panel located in the same room to connect to the 400A, 480V, 3 phase, 3 wire Distribution Panel. My question is that the existing Distribution Panel that I want to re-route the feeder to the 400A distribution panel has a 600A adjustable trip main breaker. I checked and the main breaker can be set at 400A. My question is if the main breaker is rated at 600A and I can adjust the trip at 400A, is it allowable to connect to the 400A, 480V, 3 phase, 3 wire Distribution Panel since the Distribution Panel that I want to connect to has a 400A main breaker?

 

[Rock86]

So you want to know if you can put an adjusted 400A breaker ahead of a fixed 400A breaker? Is the adjusted 400A breaker feeding any other circuits?

 

[j2020]

Yes. But the adjustable trip breaker is rated at 600A but can be adjusted down to 400A. The breaker is a main on a distribution panel that feeds mechanical equipment. My question is since the adjustable trip breaker is rated at 600A, if I adjust it down to 400A and connect it to a distribution panel with a fixed 400A breaker ahead of this distribution panel, is that allowable?

 

[ron]

If the long time pickup (trip rating) is adjusted to 400A, it is a 400A breaker and can feed a 400A panel with a MCB or MLO

 

[j2020]

Great. Thanks for confirming! I appreciate it.

 

[don_resqcapt19]

You need to be sure that you comply with 240.6(C)....if you don't you have to treat it as a 600 amp breaker.

 

[j2020]

Good point... I'll make sure of it.

 

[j2020]

I have another question. If I tap the buss on the existing distribution panel and provide a feeder to the other distribution panel, can I just connect to the main breaker at the other distribution panel instead of providing an enclosed breaker next to the buss that I am tapping? The two distribution panels are next to each other. Maybe a little more than 10 feet apart. There is no physical space to provide a 400A breaker in the existing Distribution Panel.

 

[Rock86]

I'd suggest taking measurements and referring to 240.21.

 

[infinity]

I have another question. If I tap the buss on the existing distribution panel and provide a feeder to the other distribution panel, can I just connect to the main breaker at the other distribution panel instead of providing an enclosed breaker next to the buss that I am tapping? The two distribution panels are next to each other. Maybe a little more than 10 feet apart. There is no physical space to provide a 400A breaker in the existing Distribution Panel.

As Rock stated you'll to know the maximum conductor length and then apply the appropriate tap rule in 240.21. Since you mentioned more than 10' it sounds like you'll need to apply the 25' tap rule.

 

[j2020]

Understood. Thank you, everyone.