Can a 3 Phase RCCB be used if there is no neutral?

Ideally the 3 phase RCD would be chosen where the test button actually worked - some RCDs have internal electronics , and that does need a voltage between at least some of the poles, but the makers do not always say which devices do need power to always meet the spec. 

a 3 pole rather than a 4 pole RCD may be better if there never will be a supply side neutral.

It is a simple user check to press a button marked test, and even then it is rarely done on time.  To require someone to bring a tester with them almost guarantees that testing will be omitted.

You could create your own test button of course, placing a suitable current limiting resistor either between an incoming and another outgoing phase or between an outgoing phase and earth, but really it is covering over a poor design choice. If there is no supply side neutral, is there a supply side earth ?

I'd certainly not recommend  your 'just a sticker change' approach.

Mike.

Hi Mike

Thanks for your response. I have been looking into see if there are any 3 pole versions as I didn't think the sticker option would be suitable either. I am probably going to be looking at using a 3 pole MCB with an RCD addon in order to have a functioning RCD.

Thanks

I believe that there are some TPN RCCBs whose test buttons do work without a N connection - the internal test circuit is just connected between two different Ls instead of L & N and with a higher value resistor to suit the 400V difference.

Some other manufacturers simply suggest adding a resistor between an otherwise unused N terminal and a particular line (the value being difference between what would be needed for 230V and 400V situations) to allow the conventional L-N test circuit to work.

So I think the proper answer is to pick a device whose manufacturer does suppose TP(no N) operation - by whatever approach they recommend.

   - Andy.