3 pole circuit breaker

[sparky64]

This might be a daft question, but i'll ask it anyway just for peace of mind.

i've got a 3 pole circuit breaker and a neutral bar in a dist board that's close by to a new machine. i need a single phase (230v) supply, can i use the 3 pole cb and the neutral to temporarily supply a single pole machine whilst i get a dedicated single pole supply installed. I'm not sure how the 3 pole breaker would react to an over current situation or a short circuit caused by a single pole supply.

thanks for any replies

sparky

 

[PeterW]

I'm pretty certain to use a 3 pole breaker for singke phase, you would normally loop the live so it goes into two poles of the breaker and the neutral into the third.

That way the breaker is balanced.

 

[jrwb4gbm]

Some people don't recommend doing this but I have in the past as a temporary short term setup.If you are going to use 2 poles for a 230 source , it should not matter because any phase will trip if the current rating is exceeded. That would be called a double pole application. If you are going to use just one pole for 120 volts, verify that the voltage to neutral is 120 volts. Here in the US one of the poles to neutral can be approximately 200 volts (called the "High Leg") and the other two poles ("Legs") will normally be 120 volts to neutral.

 

[DEVITG]

single phase in a 3 phase

It is just enough to use only 2 of them , one for the live phase and other for neutral , CB are not as a MOTOR GUARD , each block is independent from the other , they only have a trigger that brake on any phase fault the others blocks.

They do not balance phases as in OVERcurrent relay or Motor guard.

But you may consider than a single phase run on higher current than a 3 phase.

 

[keithkyll]

As long as the breaker is labeled "Internal Common Trip", you can use just 1 pole and be safe. I expect most breakers are built this way. An overload on any phase will cause the breaker to trip. No need to pass the neutral through it, or double up.

 

[Jim Dungar]

UL tests multipole breakers as single pole devices. I do not know what the IEC requirements are but because most breakers are now both UL and IEC there should be no issue with using a UL Listed 3-pole breaker to handle 1-pole loads as long as its 1-pole interrupting rating and voltage L-G is followed.

 

[rsdoran]

An ecerpt from a Square D catalog http://ecatalog.squared.com/pubs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QOU%20Miniature%20Circuit%20Breakers/0720CT9401R105.pdf:

Tripping Mechanisms

A tripping mechanism is an assembly within the circuit breaker molded case that causes the circuit breaker to open automatically under sustained overload or short circuit conditions.


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The tripping mechanisms in two- and three-pole circuit breakers operate such that an overcurrent on any pole of the circuit breaker will cause all poles of the circuit breaker to open simultaneously.​

Thermal and magnetic factory calibration (with current) is performed on each pole of every Square D circuit breaker.​

These mechanisms operate to trip the circuit breaker:​

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Thermal trip


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Magnetic trip


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Optional shunt trip accessory (see Accessories, page 12)


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The sensing system is an integral part of a thermal-magnetic circuit breaker. The sensing system continually monitors current flowing through the circuit breaker. It detects abnormal current conditions and, depending on the magnitude of the current, initiates an inverse-time or an instantaneous tripping response. This action causes the tripping mechanism to open the circuit breaker contacts and interrupt current flow. The speed of the tripping process must be controllable and inversely matched to the severity of the overcurrent. QOU miniature circuit breakers have an over-center toggle mechanism for quick-make, quick-break action with positive handle indication. The handle assumes a position between ON (I) and OFF (O) when the circuit breaker has tripped.​

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As mentioned the voltage must match i.e. a 480vac breaker should not be used for a 240vac application or vice versa.​

Just check the technical specs for your breaker to see if it can be used for your application.​

 

[TConnolly]

I'm pretty certain to use a 3 pole breaker for singke phase, you would normally loop the live so it goes into two poles of the breaker and the neutral into the third.

That way the breaker is balanced.

I wouldn't recommend that - this is a breaker in a distribution board. It may not be feasible to to this as one side is probably attached to the three phase buss. Just take the one leg off the breaker and tie the return back to your neutral bus. The world is full of breakers that are unbalanced to one degree or another.

 

[Lancie1]

I need a single phase (230v) supply. Can I wire between one pole of the 3 pole circuit breaker and the neutral, to temporarily supply a single pole machine?

Yes, IF your 3-phase voltage level is 380 to 400 volts. 400/3^.5 = 231 volts.

 

[sparky64]

Thanks for the replies.

I figured that it would be fine, maybe not good electrical pracice over the long term, but electrically safe is what i'm looking for and it does dig me out of a hole.

sparky64

 

[Jim Dungar]

It seems there is a terminology issue looming.

A European circuit breaker is not always the same thing as a North American device.

A European may call a protective device for a motor a "circuit breaker" where an American may call it a "manual motor starter" or a "motor circuit protector".

In the US circuit breakers which are listed under UL489 are suitable for branch circuit protection and those under UL1077 are for supplemental protection (i.e. internal to a control panel) only. In Europe these circuit breakers would fall under IEC 60947-2.

 

[Stationmaster]

This might be a daft question, but i'll ask it anyway just for peace of mind.

i've got a 3 pole circuit breaker and a neutral bar in a dist board that's close by to a new machine. i need a single phase (230v) supply, can i use the 3 pole cb and the neutral to temporarily supply a single pole machine whilst i get a dedicated single pole supply installed. I'm not sure how the 3 pole breaker would react to an over current situation or a short circuit caused by a single pole supply.

thanks for any replies

sparky

"NEUTRAL"?????

I would think if you need "single phase 230v" you would use two legs of the 230v 3ph breaker. You don't need a "neutral" to have 230v 1ph, you need "L1 and L2". L1 and neutral will give you 120v 1ph (except for the aforementioned "High" leg).

The breaker will "work" just fine, it just looks unusual and may throw someone off who is trying to troubleshoot down the road.

Stationmaster

 

[Lancie1]

Hold on, Stationmaster. Remember, he is not in the US. His voltage in England is different, probably 3-phase 400 volts. And he did say its is a single-pole device. Here it would be 480 volts, and a single pole-to-neutral produces 277 volts, a common voltage for HID lighting.

Sparky did not say what the main voltage level is, but you can easily calculate it: 230 X square root of 3 = 398 volts. I also did a Google search. English main 3-phase power is 400 volts, 230 to 240 volts from line-to-neutral.

Things are not the same, all over.

 

[rsdoran]

"NEUTRAL"?????

I would think if you need "single phase 230v" you would use two legs of the 230v 3ph breaker. You don't need a "neutral" to have 230v 1ph, you need "L1 and L2". L1 and neutral will give you 120v 1ph (except for the aforementioned "High" leg).

The breaker will "work" just fine, it just looks unusual and may throw someone off who is trying to troubleshoot down the road.

Stationmaster

The UK does not have 120 the same as the US, their home power is 230/240. As mentioned his 3PH supply is probably 380/400 with neutral, then one leg to neutral is 230/240.

 

[Stationmaster]

Hi Lancie1,

Thanks guys, for the clarification, I was "lost in the US", and you are so right, Sparky never mentioned the voltage on the main power.

I'll go back to my room now. Sorry to bother you.

Stationmaster