140M branch circuit

Is there any reason I couldn't use a 140M circuit breaker for branch circuit protection of something like a control transformer or power supply?

I could wire it for the single phase, and a transformer and motor are basically the same thing (coil winding with 6x inrush).

I've done some pricing and it seems it might be just as inexpensive to use a 140M as a fuseblock + fuses.

My concern would be the fact that these have an adjustable setting.

Those devices are UL listed as UL508 Manual Motor Starters or as "Motor Protection Circuit Breakers", but in either case, the listing has the word "motor" in it, so any use that is not a motor would be a violation of the basic "suitable for the intended use" rule. Whatever you use must have a listing as an Over Current Protective Device (OCPD), either for a Branch or Feeder, which for "breakers" means UL489 (fuses are UL 248).

A few mfrs offer versions of those IEC devices like the 140M that bear a UL489 listing as a Branch OCPD, but they will not have adjustable trip settings. The only kind of UL489 listed devices acceptable as OCPDs for other than motor loads that have adjustable trip settings are molded case breakers with Electronic Trip Units, which would not apply to small things like you are referencing.

If you want to use a CB instead of fuses though, you can use the 1489-M breakers on 480V, so long as it is fed from a 480/277 3 phase 4 wire system* (meaning they are "slash rated"). They are UL-489 listed as Branch OCPDs. Be careful on other brands of those however, a lot of them are NOT UL489 listed, they are "supplementary" protectors under UL1077, which means they MUST be used with another UL489 or 248 listed OCPD ahead of them, which make them pointless.



*Then again if you have a 480V delta system, you cannot use the 140Ms either.

Thanks for the reply.

I see the 1489-M breakers are only 10kA, however, so I'm going to look for other options I suppose.

I sure wish I could get my hands on UL508, but $715 is steep for a PDF, so I have to take everything by second-hand knowledge. I've done pretty well so far, my last 3-4 panels that went through UL inspection passed with no issues.

I always appreciate the answers here.

Is there an isolation transformer feeding the panel you are designing?

If you are worried about the 10KA of the 1489-M breakers, it may not matter after you take into account the peak let through of the transformer.

Just an idea

read post #2 from jaref.

the devices have to be listed for that purpose.
james

I was looking the same information up today and I did notice, for what it is worth, that the 140M instructions do have (2) places they mention setting the device for control transformers.

Doesn't seem definitive enough for me to chance using it, but thought I would mention it.

For anyone who finds this thread:

The 140U is what I was looking for. Same footprint as 140M, but designed for transformers & power supplies.

Rson said:

For anyone who finds this thread:

The 140U is what I was looking for. Same footprint as 140M, but designed for transformers & power supplies.

Click to expand...

Yep, always fun.


Might want to read this:






Rockwell Automation announces that as of March 2022, our Bulletin 140U Molded Case Circuit Breakers will be discontinued and no longer available for sale. To support your transition, we recommend you migrate to our Bulletin 140UT Molded Case Circuit Breakers.