3 Pole Circuit Breaker On Single Phase System

On a typical bolt in or stab-lok style of distribution panel, where all 3 poles of the breaker must contact a phase bus, won't this be a tad bit difficult?

I second PWSlack. Most workable solution and I have applied it without any problem for quite sometime.

(The purpose of the foregoing is to make sure that all three poles of the CB "see" the load current, as necessary for proper sensing. The same princlple applies to 3-pole motor overload relays used on 1-phase motors.)

I saw an installation like this and wondered what was going on.

Shouldn't any pole that exceeds its rating pull all three out (hence the bar that mechanically interlocks all 3 breakers)?

IEC circuit breakers and overload relays have a feature called a differential trip bar. This is used to help the device trip quicker if there is a loss of phase. All that is necessary is that current is flowing on all 3 legs.

In typical North American design circuit breakers this is usually not necessary, that feature is not part of the trip mechanism. But being that many NA companies are now owned by companies that also make IEC products, that is changing. If you are unsure which type it is, there is no harm in doing the loop-through technique on a NA designed breaker.

Thanks. Seems I've some googling to do.

methinks Mr. Slack shouldn't be wiring in the US

Why?

And why not? With thinking nobody here gets wiser. Please tell us why?

If as the OT posts there are 6 terminals on that breaker, to connect with 6 wires.

He will only have 4.

His proposal goes wrong only when it is a plug- in system, and still then 1 phase is missing to create a short cut.

I did it also with using just 2/3 of the breaker with a cut of the connection handle, that unlocks the non- used one.

PWSLACK's method of wiring the 3 pole breaker for two pole usage has been used in the US for years. This is also how larger DC motor systems are wired.

Just to be clear, the reason DC is wired that way is because it is much more difficult to interrupt the arc with DC, so using multiple poles in series increases the cumulative air gap so that a reasonable DC voltage can be used. It has nothing to do with the current sensing, again with regards to NEMA designed MCCBs.

Thanks, I did not know that.

20100831132300.pdf‎ (39 KB‎)

A circuit breaker is just an overcurrent and short circuit circuit protection. you dont have to use all 3 Phases and the loads dont have to be balanced. You could just use 2 phases on a 3 phase circuit breaker, with no problems.

Think about it, you could have a 3 phase circuit breaker feeding a sub main board, the load connected to the sub main board may not be balanced, but it wont trip the 3 phase CB unless the is an overload contition.

Cheers

Joe

Joe, read my post. For those of us here in the US, you are right, it makes no difference. But for people outside of the US (and this is a very international forum) it does make a difference. THEIR style of breakers may nuisance trip if you only use 2 out of 3 poles.

JRaef Sorry mate I was only giving my input, but now that we are on the subject.

I would like to ask you a question: I have a main distribution board the is suppling various sub boards within a factory. The Sub boards have single phase loads these may not be ballanced are you saying that I would have to ensure that loads are always ballanced, that is a croc!

You could for instance have oh, lets say an injection molder that has single phase heating loads connected, these are temperature controled they will switch of an on depending on the actual temperature, loading on each phase will change dependent on what is heating, current will change on each phase dependant on what is on not heating, are you going to say that because we have an inballanced load that this machine is going to switch off?

Circuit breakers are circuit breakers they are designed to trip at a point of over-current over a given time, they do not discriminate on ballanced load. They only look at overloaded conditions and short circuit conditions or anything in between.

I do realise that this is an international forum, I have traveled the world but I have not been to all destinations, but I have been to many destinations that you would never put on your holiday list, even though they may not have the same standards as we would have circuit breakers are the same; Please advise me where circuit breakers are not circuit breakers as we understand.

Best Regards

Joe

By the Way JRaef

I dont live in the US, I live in New Zealand, that is if flying from LA you will pass over it just before you hit Australia

Cheers

Joe

You should put all the 3-poles in series for better functioning of the tripping mechanism of the 3-pole breaker when using it for single phase application.

Replace the 3-pole breaker with a 2-pole breaker.