3 pole MCCB vs 4 pole MCCB 3

[darrenyee88]

Hi All,

Can someone explain to me the advantages of 4 pole MCCB over 3 pole MCCB ?

Regards,
Darren

 

[FreddyNurk]

There isn't an explicit advantage, it depends on your application as to whether you need 4 poles or not.

If you have a need to disconnect the neutral at the same time as any of the phases in a 3 phase AC system you'd use a 4 pole breaker. If not, you'd use a 3 pole.

For an LV DC system, depending on voltage, you might need 4 poles in order to successfully break the DC arc.

EDMS Australia

 

[144x]

Here is a case where using 4 pole breaker may prevent mal-tripping in other feeders

 

[Mbrooke]

I believe a TT system requires 4 poles.

 

[krisys]

In general for oil and gas industry, specifically, where it is necessary to deal with the hazardous area environment, applying 4-pole MCB is a mandatory requirement, not just a choice. AT the location where I work, it is IEC system with 415V, 3-Φ 4-wire system.

For other locations may be discretionary based on the cost v/s benefit analysis.

 

[darrenyee88]

@FreddyNurk (I understand from my contractor that they need to remove the connection of the neutral line in order to conduct safe maintenance activities. Is this true. I am mechanical engineer who does not have much electrical knowledge pardon me for my stupidness. Thanks.

 

[waross]

It depends.
Some sectionalizing and transfer arrangements may need a four pole breaker in order to properly monitor ground fault currents.
This is particularly true for impedance grounded systems but may apply to some solidly grounded systems also.
In the NEMA world the standard, unless special conditions apply, is a three pole breaker.
This also applies to a large portion of the oil and gas industry.
Some designers strive to arrange the grounding so that a four pole transfer arrangement is NOT needed.
A four pole transfer arrangement adds at least two more possible points of failure.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Rules on this issue vary by country and you don't say where you are working. It makes a difference.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[MatthewDB]

Rules on this issue vary by country and you don't say where you are working. It makes a difference.

Bingo!

In North America, it should never be needed. 4 wire systems must be solidly grounded here. Resistance grounded or floating systems MUST be 3 wire and only contain line to line connected loads. Dedicated transformers must be used for 277V (or 343V) loads.

Under IEC wiring rules, TT and IT systems can and usually do have line to neutral loads. In this case, the neutral must be switched to protect against the neutral shock hazard and to protect against double fault conditions. (Imagine a scenario light fixture with a neutral - earth short and then a big motor grounds out. If that lamp circuit doesn't contain a neutral breaker, the neutral will burn.)

 

[darrenyee88]

@jraef Singapore