Running the Neutral Through a Circuit Breaker

[Paulm]

Hi Guys,

I have been asked to install some cabling in an industrial site.
This is all engineered by an aussie company. Part of the spec is to install a multicore cable as a voltage reference from a metering cabinet to be measured in a control cabinet.
This is 3ph and Neutral, all tapped off HRC fuses, then run to a 2amp, 4-pole MCB, then run to the other cabinet for monitoring.
What are the requirements/limitations around breaking the neutral please?

I guess it doesnt have to run through a breaker?
Can I run 3ph through a 3-pole MCB and Neutral through a 1-pole MCB as they are also suggesting?
I am thinking of temporarily runing phases through a breaker and Neutral straight out - no problem?

The metering and control cabinets are just a couple of meters apart.

Thanks

[Paulm]

short answer no, the switched neutral must be arranged to switch substantially together with all active poles, or not switched at all

AS/NZS23000:2007
2.3.2.1.1 (b) (ii) (a)

[Paulm]

Thanks so much Greg - I didn't think you could switch the Neutral separately.
It would be ok not to switch the Neutral at all though, yes?

[Paulm]

4 pole switch/circuit breaker, the clause in 3000 (see previous post) contains all the info

[Paulm]

Yes I did read that - thank you for the reference - and it doesnt say the break is required for the neutral.
Thanks again

[Paulm]

basically if you are going to switch the neutral this is how it must be

[DougP]

A circuit breaker isn't necessary for the neutral (except for some specific circumstances), but can be connected through the same circuit breaker as the actives as Greg says. Same as RCCBs or RCBOs switch the neutral.

But, in your original post you said "all tapped off HRC fuses" - hopefully you aren't meaning that the neutral is also through a fuse? That is also not allowed.

If you're not sure why the neutral can't be switched separately - the basic reason is because if the neutral is disconnected without the associated actives being disconnected, then the neutral will then become live with respect to earth/neutral.