Control Cabinet Installation

[Kerry White]

In an industrial application, where I have a control cabinet being fed by a 20A 3-phase breaker from the main panel, I know I need to have a main disconnect at the control cabinet, but does the control cabinet have to have a main circuit breaker inside of it?

I looked at using a Supplementary Protector as opposed to a primary for cost reasons, but I really don't know if that is right or not.

Any help will greatly be appreciated.

Thanks.

 

[Jraef]

In an industrial application, where I have a control cabinet being fed by a 20A 3-phase breaker from the main panel, I know I need to have a main disconnect at the control cabinet, but does the control cabinet have to have a main circuit breaker inside of it?

I looked at using a Supplementary Protector as opposed to a primary for cost reasons, but I really don't know if that is right or not.

Any help will greatly be appreciated.

Thanks.

Is UL listing an issue? UL will not allow the use of a "supplementary" breaker in the enclosure unless the proper upstream OCPD is in the same enclosure, which makes it impractical to use them as a main CB. In addition, you will most likely need an SCCR rating on the entire panel and a supplementary device has virtually no SCCR rating. I also don't know of any door interlocking mechanisms for supplementary breakers, so how would you do that?

You could, however, use a non-fused disconnect in the panel if the feeder breaker is already properly sized for the load in the panel. You don't absolutely have to have the OCPD in the circuit duplicated, although a fused version is not very much more expensive for something that small.

 

[Kerry White]

Thank you for your response!

No, I do not want to have to buy another circuit breaker because I'm feeding this panel with a circuit breaker from a sub panel. This feeder breaker is sized right for the inrush current for this panel, and we've done our NFPA 70E studies on it so we can categorize the panel accordingly.

I only wanted to know if I needed that redundant circuit protector in the cabinet or will a disconnect work for lock-out tag-out purposes. I'm hoping I can just install a door mount disconnect and be "ok" as far as UL and Code is concerned. Any suggestions?

Thank you for the supplemental breaker information and UL, I didn?t know that. Just curious, where can I find more information about that?

 

[Jraef]

Thank you for your response!

No, I do not want to have to buy another circuit breaker because I'm feeding this panel with a circuit breaker from a sub panel. This feeder breaker is sized right for the inrush current for this panel, and we've done our NFPA 70E studies on it so we can categorize the panel accordingly.

I only wanted to know if I needed that redundant circuit protector in the cabinet or will a disconnect work for lock-out tag-out purposes. I'm hoping I can just install a door mount disconnect and be "ok" as far as UL and Code is concerned. Any suggestions?

Thank you for the supplemental breaker information and UL, I didn?t know that. Just curious, where can I find more information about that?

most of the mfrs who sell the supplemental breakers will have white papers on how to use (and not use) them. Do a search on "UL1077 vs UL489" and you should find something. UL1077 is the spec for supplemental breakers, UL489 is the spec for traditional breakers. But to be fair, UL1077 devices can also be backed up by fuses.

So back to your situation, yes, you can just use a door interlocking non-fused disconnect switch as a local main disconnect. You don't need to repeat the OCPD if you already have one dedicated to that circuit.