Circuit breakers: 3ph VS 1ph 3

[giuseppe]

Hi to all.

I have a simple question that may have a complicated answer: when testing a three phase Circuit Breaker with a single phase Current Injector, what will happen if the test is carried out only on one pole (line-in/line-out). I am presently far away from a laboratory and I cannot carry the test myself. I always tested the correct intervention of a three phase CB injecting to the Phase L1 (or A) and, with proper jumpers, exit from Phase L3 (or C). I cannot remember what then happen if each phase is tested individually. I think it would trip earlier than expected, but...I am not sure of it.

Could anyone out there help with this issue?

Thank you very much and kind regards.

Giuseppe

 

[unclebob]

If the trip unit of your circuit breaker has a ground fault element, it will trip the breaker when testing one phase at a time. You will need to defeat it somehow with a jumper...

 

[Zogzog]

Besides the GF problem single phase testing will work just fine in 99.9% of the tests. Unless something bizare happens like the internal CT's in the trip unit somehow have polarities reversed, saw that happen once with a ABB SS box.

 

[giuseppe]

Hi Unclebob and zogzog,

thanks for your reply.

The breaker is a Moulded Circuit Breaker, and as I have to supply from the breaker three individual single phases (Phase plus Neutral), I am unsure what the behaviour of the tripping device will be if one or two of the phases will be switched off by the downstream contactors. My fear is that the breaker will open at a lower Thermal Load.
In the past, when I was supplying Single phase Systems from a three phase Board, I always used fuses, but nowadays...

Thanks for your valuable help on this issue.

Kind regards.

Giuseppe

 

[oldfieldguy]

If the breaker is thermal-magnetic, expect the trip times to decrease for adjacent poles as thermal pre-loading takes place. This effect is usually noticeable.

Magnetic elements (instantaneous) won't be affected.

old field guy

 

[waross]

I'm with oldfieldguy on this.

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

 

[Zogzog]

Yep he is right, I assumed we were discussion a power circuit breaker, not a MCCB with thermal elements.