(3pole + N) vs 4pole Breaker

http://cr4.globalspec.com/thread/54103

I am reffering for the load side. I've seen welding outlet that using 4pole breaker while package motor is using 3pole+N . Both of them are using 4core means they have neutral. The voltage is 415V. Note (3P+N) means 3pole is overcurrent while N is just a switch connected in the breaker.

Follow the electrical codes applicable in the country of installation. In the UK, for example, it would be British Standard 7671.

Ask the Client.

3p + n would be for a nice clean known load. If you are specifying a 4 pole breaker it may because you have have issues with harmonics and that the current in the neutral can be higher than the phase conductors. (Schneider do a good paper on a transformer with this issue.)

Years ago neutrals used to be dead but with the rubbish thats on them now it pays to treat them as live conductors with respect to earth.

2 pole MCBs are usual on a tool transformer where you have 55 -0- 55V. Although its known as a 110V supply both poles are live with respect to earth.

Neutrals are often solid because of the problems that might occur if you broke it before the phases on a TP&N distribution board say feeding lots of lights.

This said it is far from an exact science.

to find an answer to your problem first you should understand Star and delts circutes and three phase circutes!

System deigner selects the same.

Normally, Neutral is not allowed to break in any conditions, ( except special applications)

for human & equipment safety. So, for single incomer power fed systems, 3P+N breaker is used, where, only phases are isolated during breaking operations.

But, in multi incomer power fed systems, you need not to mix up the neutrals of incoming powers, where, you can use 4P breakers, to isolate the other power sources neutrals from the incomer power neutral in use.