Reducing Feeder Size on Adjustable Breaker

[sbutler]

If you have an 800-amp breaker that can be adjusted down to 600-amp, can you use 600-amp conductors or do you need to use 800-amp? Where is this allowed in the code?

 

[lauraj]

According to 240.4, it looks like it depends on the design of the adjustment means:

(B) Adjustable-Trip Circuit Breakers. The rating of adjustable-trip circuit breakers having external means for adjusting the current setting (long-time pickup setting), not meeting the requirements of 240.6(C), shall be the maxi- mum setting possible.

(C) Restricted Access Adjustable-Trip Circuit Break- ers. A circuit breaker(s) that has restricted access to the adjusting means shall be permitted to have an ampere rat- ing(s) that is equal to the adjusted current setting (long-time pickup setting). Restricted access shall be defined as lo- cated behind one of the following:
(1) Removable and sealable covers over the adjusting means
(2) Bolted equipment enclosure doors
(3) Locked doors accessible only to qualified personnel

 

[david luchini]

If you have an 800-amp breaker that can be adjusted down to 600-amp, can you use 600-amp conductors or do you need to use 800-amp? Where is this allowed in the code?

See 240.6(B) and (C).

 

[kwired]

But there is nothing wrong with installing an 800 amp fused disconnect and using fuse reducers to install 600 amp fuses - and supply 600 amp conductors with that, or installing an 800 amp fused disconnect and installing 700 amp fuses and supplying 700 amp conductors.:blink:

 

[iwire]

But there is nothing wrong with installing an 800 amp fused disconnect and using fuse reducers to install 600 amp fuses - and supply 600 amp conductors with that, or installing an 800 amp fused disconnect and installing 700 amp fuses and supplying 700 amp conductors.:blink:

:roll:

Are you actually complaining the NEC is being practical?

Maybe bring up how the NEC requires a breaker to open all ungrounded conductors at once in many cases but does not require the same of fuses.

 

[kwired]

:roll:

Are you actually complaining the NEC is being practical?

Maybe bring up how the NEC requires a breaker to open all ungrounded conductors at once in many cases but does not require the same of fuses.

Not sure if I was complaining or not. I guess the :blink: at the end sort of made it seem that way. I don't really know what to think about why the adjustable breaker has different rules then a fuseholder that can accept a variety of fuses and adapters.

 

[petersonra]

But there is nothing wrong with installing an 800 amp fused disconnect and using fuse reducers to install 600 amp fuses

I seem to recall the fuse reducers are not listed. That could be an issue.

 

[kwired]

I seem to recall the fuse reducers are not listed. That could be an issue.

Take a look at this. None of the class J fuse reducers are listed, I think the rest are. Some of them are not CSA but are UL listed.

 

[iwire]

I seem to recall the fuse reducers are not listed. That could be an issue.

What NEC section requires them to be?

We used to have a customer that always specified one size larger fuse bucket than needed in their main service gear so every fuse had to have reducers installed.