Circuit breaker protection for a neutral conductor

[Tradie]

Have you ever seen a neutral incomer connected to a single pole circuit breaker on a 3 phase electrical installation ?

It was a first for me.

[GCE]

Whoever did that does not understand 3 phase electricity systems and has obviously never read SANS 10142-1

6.9.2.1 A neutral conductor shall not have a single-pole disconnecting device.

[Tradie]

I would go so far as to say that even using a 4 pole circuit breaker is not a smart idea, the neutral should be an isolating bridge, Like the geyser combo breaker isolators.

Looking at the way many people do the double pole DC fuse disconnect, might not be such a smart idea, I would say a solid bridge should be fitted for the negative and a fuse for the positive, but that is a discussion for another day.

It was scary to see how quickly the smoke starting pouring out of the CBI ASC unit. I did open it up to check the damage, I noticed they do have 1 MOV which I want to remove to see it it opened, I do know one of the capacitors blew and the big main resistor also had a massive flash and smoke.

The other ASC unit that blew, I sent it back to CBI but they just indicate that it is out of warranty, so I am trying to get it back so that I can strip it and see if I can repair it, the board is pretty straight forward it has all the component marking so I will be able to pop in to the electronic shop and get spares. wifi module which might still which I could use if I cant fix it.

Whoever did that does not understand 3 phase electricity systems and has obviously never read SANS 10142-1

6.9.2.1 A neutral conductor shall not have a single-pole disconnecting device.

[Tradie]

Let this be a warning to any electrician who feels the need to fiddle with 3 phase power, never ever ever switch or fuse the neutral only on a 3 phase system, unless you know what you are doing.

Make sure you understand 3 phase systems, especially on backup and solar systems which require neutral switching.

[Dave A]

I would go so far as to say that even using a 4 pole circuit breaker is not a smart idea, the neutral should be an isolating bridge.

With a 4 pole breaker on a three phase supply, the neutral should be on a slow-break fast-make contact so that the neutral conductor is the last to break contact when disconnecting, but makes contact before the phase conductors when connecting.

[Tradie]

Agreed, but also no thermal protection, unless specifically designed for the application.

With a 4 pole breaker on a three phase supply, the neutral should be on a slow-break fast-make contact so that the neutral conductor is the last to break contact when disconnecting, but makes contact before the phase conductors when connecting.