Incoming 3 phase, using 4 poles MCCB?

[ckchew666]

Hi guys,

I need some help on the electrical design. One of our client site has 3 phase 415 (no neutral), can we use a 4 pole (with neutral) MCCB. Without connecting the Neutral pole at the MCCB will it cause any danger/fault to the system?

I've not done this before, anyone with experience please clarify me. The MCCB delivered wrongly and we are running short of time to change another unit (import unit - Siemens).

Thanks.

 

[leitmotif]

Using only 3 of the 4 poles on the breaker may be allright
PROVIDED there is no instrumentation connected to that pole ie current transformer, etc etc which may go to protective circuitry of breaker ie trip actuation etc.

Dan Bentler

 

[keithkyll]

The breaker should have 'internal common trip'. An overload on any pole will cause the entire breaker to trip. It's safe to use. I wouldn't ship a machine that way.

 

[ckchew666]

Using only 3 of the 4 poles on the breaker may be allright
PROVIDED there is no instrumentation connected to that pole ie current transformer, etc etc which may go to protective circuitry of breaker ie trip actuation etc.

Dan Bentler

Ok, thanks for the information, I don't have any CT there.

 

[ckchew666]

The breaker should have 'internal common trip'. An overload on any pole will cause the entire breaker to trip. It's safe to use. I wouldn't ship a machine that way.

"I wouldn't ship a machine that wa" May i know what do you mean? You foreseen any problem in future?

"An overload on any pole will cause the entire breaker to trip." I just worry that with any open pole (neutral) whether the other 3 poles will be able to trip if any of the pole overload or it'll always be tripping due to an open neutral pole.

Anywhere..thanks for your feedback.

 

[aussiesurf]

there is no problem in doing this as the 3 poles are commonly connected apart from the neutral.

 

[ckchew666]

there is no problem in doing this as the 3 poles are commonly connected apart from the neutral.

Thanks for your info...appreciate it.

 

[keithkyll]

"I wouldn't ship a machine that way" May i know what do you mean? You foreseen any problem in future?

No. I've seen contactors with unused poles, but not breakers. The issue is cosmetic. It may violate a code.

"An overload on any pole will cause the entire breaker to trip." I just worry that with any open pole (neutral) whether the other 3 poles will be able to trip if any of the pole overload or it'll always be tripping due to an open neutral pole.

An overload on any pole will cause it to trip. It doesn't matter if one pole isn't wired.

 

[Bob A.]

If a 3 Phase feed has 3 lines, it is referred to as "Delta" and when 4 are present, it is referred to as "Wye" with the 4th line being a neutral which is grounded by the utility at the pole.

The Delta is more of an " Industrial" service and the 4 Wire Wye is more of a "Commerical" system in that it permits both 3 phase and single phase loads to be easily addressed in a single utility service.

In your case, you can go phase to phase and measure 415 VAC and if you check phase to neutral expect to see 415 / 1.732 = 240 VAC single phase.

I am not aware of any case where opening the neutral would provide any additional protection, but some of those writing codes are "misguided do-gooders" and I would not rule out this possibility.

Best Regards,

Bob A.

 

[Jim Dungar]

If you are building a machine rated for 415V, it is probably not being installed in the US. What codes are you worried about violating?

The US NEC does not apply to industrial machines, except in the area of grounding/earthing and fault current ratings. The UL489 standard for circuit breakers does not care if a circuit breaker pole is left unused.

Most 4 pole breakers are designed so that only three poles sense current and the 4th pole is nothing more than a switch. It is common in Europe for a machine disconnect to open and isolate all of the supplconductors (hots and neutral) except for the earthing connection.

 

[parky]

Be very careful in switching the neutral, ensure that the 4th pole is not late early break/late make or any 240v electronics (psu's plc's & single phase inverters) can pop!.
Some isolators are arranged this way however if it is a full isolator with trip it will not have the early break contact.
The only times that I have known the 240v stuff to pop is when someone left out the neutral link & switched on the 415 isolator & someone fitted a motor type 4 pole isolator as a secondary isolator & again as the 4th pole was early break/late make it popped 4 inverters & the power supply.
I would prefer to use a proper 4 pole switch dissconect with thermal trip & never use a removable neutral link for the above reasons