Single phase mcbs on 3phase circuits.

[lyledunn]

A client of mine has a number of small 3phase motors some wired via starters some not. All are protected by a single phase mcd on each phase rather than the linked 3phase type.
I think that I am reasonably ok with the technical disadvantages and I will relay these to my client. However, there is no breach of our Wiring Regulations (UK and Ireland). Is there any reference to this situation in NEC Code?

Regards,

Lyledunn

 

[busbar]

Potential equipment damage and personnel hazard from a non-ganged disconnecting means are some primary concerns.

 

[rbulsara]

NEC prohibits use of 3 single pole breakers as a 3 pole breaker unless their handles are tied together (by factory assembly) by a common bar so that all opens and closes simultaneously.

And by any stretch of imagination the you described is dangerous and unprofessional. I cant imgaine UK and Ireland regualtions are that poor.

 

[jbartos]

Suggestion: NFPA 70-2002 limits usage of single phase or one pole circuit breaker for single phase loads in Article 240-20(B)(1):

(1) Multiwire Branch Circuit. Except where limited by
210.4(B), individual single-pole circuit breakers, with or
without approved handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads.

 

[lyledunn]

rbulsara,
The UK Regs is a comprehensive document based on IEC 364. However, it is not uncommon to use fuses to protect circuits and thus the same disadvantages apply. In this egalitarian world it may have been regarded as somewhat bias to apply sanctions to mcbs???

Regards,

Lyledunn

 

[rbulsara]

lyledunn:

For a overcurrent protection your statement is true but not for a disconnecting means. Fuses (for 3 phase motors) are invariably used in conjuiction with a 3 pole disconnect switch which is required to open all 3 poles simultaneously.

NEC 430.103 states " The disconneting means shall open all ungrounded supply conductors and shall be desinged so that no pole can be operated individually."

When 3 pole circuit breaker is used it serves as both the overcurrent protection and a disconnect. A disconncet cannot open a pole individally for saftey reasons. (Requiring only one manual operation for disconnection, to minimize chance of error and accidents).