Using three phase MCCB for singel phase lighting circuits.

[michaelLeeKH]

I have some lighting circuits connected to a three phase system. For normal running, three phases will be used for lightings. When the normal supply is not available, the generator kicks in but it will onyl be able to supply one phase of the lighting instead of three phases. This is done through a switch.
However I am only using one three phase MCCB at the distribution board. Will there be any problems in supplying single phase circuits with three phase MCCB?

 

[jraef]

Unusual, but I don't see why it would not work. Each pole of a 3 pole MCCB is going to have its own sensing element, both for magnetic and thermal trips. It wouldn't matter if power were on the unused phases or not from that perspective, as long as you, and any future user, are absolutely sure that there are no 3 phase loads connected to that circuit.

That said, this situation is so unusual that I seriously doubt it is covered in any electric installation codes. So if inspectors in your country are anything like those here in the US, they have the ultimate authority and can reject anything they are not comfortable with, especially if it is not covered by regulations. That part where I said "...and any future user..." is a potential sticky point in my opinion.

By the way, some newer electronic trip circuit breakers have built-in phase loss protection that may get in the way. Under Voltage Trip coils would be a problem as well. Another potential pitfall is if the breaker has a shunt trip coil for fire shutdown, you would want to make sure the shunt trip coil power is coming off of the generated phase.

 

[wareagle]

"I have some lighting circuits connected to a three phase system. For normal running, three phases will be used for lightings. When the normal supply is not available, the generator kicks in but it will onyl be able to supply one phase of the lighting instead of three phases. This is done through a switch."
I sounds like you have 3 single phase loads connected to 3 single phase conductors A,B and C. Therefore the generator will be supplying a single phase voltage to the lights. I am having a problem with how you will connect the 3 circuits to the single phase conductor from the generator. If the loads are all on the same phase normally, then no problem.

 

[controlsdude]

Not sure about your grounding that your using? If a high or low resistance or no resistance grounding system then you need to look at NEC 250.36 high impedance grouded neutral system. I believe it specifically talks about having single phase loads attached to high impedance grounded neutral system.

 

[michaelLeeKH]

On board A, three phase MCCB supplies the lighting board, Board B, which supplies the lighting circuits. Each phase supply one circuit of the lighting, therefore under normal condition, three phases are supplied to the lighting boards, Board B by a three pole switch. During emergency condition, only single phase from board A will be selected to the lighting board, Board B, by switching only one of the three phases. This is because the generator for the emergency supply does not have enough capacity to supply all the lighting.

Can the three phase MCCB at board A be used for this application?

 

[waross]

Well if you are only supplying one phase of board "A" from the generator, that will feed through the MCCB to board "B" on the energized phase. It will work fine with an older breaker.
You may have issues with a newer electronic trip breaker as noted by jraef. If the generator is supplying lighting only, you may be able to install the transfer switch after the MCCB.
respectfully

 

[davidbeach]

This would really only work if you are not subject to any electrical inspection. It may well work in that the electrons would find the right path, but it wouldn't be a proper, code compliant, installation. Put in a proper ATS and feed the emergency loads from downstream of the ATS.