RCD without neutral 2 phase supply

[humbayd]

Hi everyone,

Quick question can you fit an RCD without any neutral connections?

If I have a 3 pole circuit breaker which has all 3 poles terminated with a 3 phase supply (L,L,L excluding neutral or earth) on the primary side and I am using only 2 phases on the secondary side (L,L) to create a 400v supply to a transformer, can I connect an RCD to this breaker?

 

[humbayd]

If the DB has a matching 3P RCBO at a sane price that is the simplest solution.

Also fitting the 3P MCB and 4P RCD as if a full 3P+N load is needed, and just using Lx & Ly for the single 400V load is perfeclty reaonable and ensures the RCD works as intended. If in the future you need any other use, it is ready to go.

Thanks for your detailed explanation and response

 

[sinewove]

The distribution board has 3 phases coming into it and is terminated to a 3 pole circuit breaker, but on the secondary side we are only using two phases. So wanted to know if I can connect an RCD to monitor the 2 phases.

In the past have seen a resistor,(100k or 100? ohm)connected between one phase and N on a 4 pole rcd so that the test button will work as normal and the unit will operate on 1,2 or 3 phases.
Regards,S