Is using three single pole molded case circuit breakers in lieu of one three pole acceptable ? 3

[bdn2004]

I was looking at a design of a control panel someone fabricated and they are using 3 Allen-Bradley G050 single pole motor protector type circuit breakers for fractional motors that kick on and off via a break in the power circuit.

The mfg writing on the circuit breakers says they are rated 6A at 277, but they are operating at 480V.
There's not a tie on the levers.

This looks odd to me...is this acceptable practice? They could have used fuses which would have done the same thing.

 

[waross]

Are the loads line to line? If so this is unacceptable on 480 Volts.
They may be used for line to neutral loads on 277/480 volt supplies.
If the motors share a neutral conductor this is unacceptable and a possible life safety issue.
For control and protection on a single phase 480 Volt circuit you may interrupt one line.
For safety isolation and for overload and over current protection you must break both hot lines and so must use a two pole switch, breaker or motor circuit protector.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

If those breakers are powering 1-phase motors connected line to neutral then yes. If all 3 phases/breakers power one 3-phase motor then no.

277V is the L-N voltage of a 480V wye connected system. So, that voltage rating of the breaker might be OK depending on the system configuration.

 

[DTR2011]

What about single phasing the motor if one leg trips?

 

[bdn2004]

https://www.radwell.com/Shop?source...MI6png8MCY3wIVBoVpCh14qACKEAQYASABEgIrNvD_BwE

Here's a picture of one of these...

Looks like there is a short bar between the levers. So I guess they are tied together.

But as you can see in this pic, it is only rated 277V? In the cabinet I'm looking at, there is a wire on each pole so I'd assume this is 480V.

 

[bdn2004]

oops here's the final answer....

This is the 1492 Allen Bradley series motor circuit protector. The 2-pole and the 3-pole breakers are indeed rated 480V, the 277V writing on one of the seemingly circuit breaker poles, is for an auxiliary contact (it's not a pole). The motors are operating 480V single phase.

False alarm, thanks for the answers though.

 

[jraef]

So that old series of breaker (circa 1993) was only UL recognized as a "Supplementary Circuit Protector" under UL1077. That means it is NOT allowed to be used as the only SCPD in a circuit, it must have another UL489 listed branch circuit breaker ahead of it or a listed Branch Circuit protection fuse. They were also only listed for use in 480/277V 3 phase 4 wire systems, you cannot use them if the line source is 480V delta. Back in those days they didn't make that clear enough on the labeling, hence their obsolescence when the rules changed about proper labeling of what are called "slash rated" breakers back around 2002. "Slash rated" means the 480/277 issue; no more than 277V line to ground. In a delta power system the line to ground potential is 480V and there is more energy in a fault than this type of breaker can withstand. Delta power systems only exist in North America, those DIN rail breakers were designed for the IEC market where that isn't an issue, hence the original marketing mistakes here in calling them "480V" when in fact they could not be safely used in some 480V installations.

And to that point if someone is selling this to you as a new system, they are using old obsolete breakers, either used or surplus. A-B stopped selling that specific line 2 decades ago or so. Their current versions are now UL listed under UL489 as true circuit breakers (although they are still slash rated, as all of those DIN rail breakers are).


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