When do I use a 4 pole breaker or disconnect?

[jpl5085]

I am trying to find documentation that talks about when to use a 4 pole circuit breaker. Is there a source that specifies the countries that still use a 5 wire power system(i.e. 3 phases, N, PE) that switches the neutral?

I would appreciate any help in this matter.

 

[Darrick]

Yes, its a practice here to use 4pole breakers at service provider incoming.

 

[mdslmn]

Power distribution with neutral conductors in TT requires the use of 5 Pole Earth Leakage Circuit Breakers on final DB's.

 

[cuky2000]

I don’t know any code or standard that recognizes more than 3 pole circuit breaker in the USA. However, in the IEC marketplace it is very common to use of 4-pole circuit breaker mainly used to isolate the neutral during ground fault event.

Earth leakage circuit breakers can be used in TN-S, TN-C, TT and IT network systems or with others words in all places where neutral and protective conductor are separated (See Earthing Classification below).

The enclose catalog and the thread for additional detail for multipole circuit breakers.

http://www.squared.com/us/products/...0cce6b852567610064e493/$FILE/0860CT+Sec04.pdf

thread249-10228


<sub>Erathing System Classification:
The first letter indicates the type of supply earthing.
T - indicates that one or more points of the Supply are directly earthed (for example, the earthed neutral at the transformer).
I - indicates either that the supply system is not earthed at all, or that the earthing includes a deliberately-inserted impedance, the purpose of which is to limit fault current. This method is not used for public supplies in the UK.


The second letter indicates the earthing arrangement in the installation.
T - all exposed conductive metalwork is connected directly to earth.
N - all exposed conductive metalwork is connected directly to an earthed supply conductor provided by the Electricity Supply Company.

The third and fourth letters indicate the arrangement of the earthed supply conductor system.
S - neutral and earth conductor systems are quite separate.
C - neutral and earth are combined into a single conductor.</sub>

 

[peebee]

cuky - 4-pole breakers are recognized in the US, but not often required. One notable exception is where multiple 4-wire generators back up multiple 4-wire service entrances; 4-pole breakers or transfer switches are often required in such installations depending on exact configuration and conductor length between sources.

 

[IsoPower]

A 4-pole breaker or disconnect is required for 3-phase ungrounded systems in Europe where they are allowed to have a neutral conductor. A neutral conductor is not allowed in the U.S., therefore, there would not be a reason for using a 4-pole breaker.
The 4th pole is necessary when using a neutral in an ungrounded system. This is necessary since a single phase-to-ground fault will cause the neutral to rise to, say, 277V in a 480V system. Without the 4th pole, this becomes a real safety issue!