Linking RCDs in 3-phase setup...

[medistat]

Doing a small woodwork shop and putting RCDs on each of the 3 phases at the supply point (it's a sub-board).

Question is do all 3 phases need to be physically linked with a bar so that one popping takes the entire three phases out? In other words, can we fit 3 x single phase RCD's or does it have to be a three-phase one-piece unit?

Can't find anything in the big book about it. Customer keen to have each pase separate as about 50% of the machinery is single phase and eg a planer stopping in the middle of a long run will cost some big dollars.

[gregmcc]

if supplying single phase circuits then no, but if supplying a 3 phase socket or machine then all 3 must be disconnected at the same time.

[medistat]

Mmmm, thanks, so one 3phase RCD plus 3 x single phase RCDs in this case.

[AlecK]

There is NO( requirement to link mcbs on 3-phase circuits.
It's perfectly OK to use individual overcurrent protection devices (fuses or mcbs).
However the devices for each circuit must be grouped / labelled to show the association between them [2.9.5.2].

The only case where linking is mandated is for common-neutral final subcircuits [2.2.1.2].

[medistat]

There is NO( requirement to link mcbs on 3-phase circuits.
It's perfectly OK to use individual overcurrent protection devices (fuses or mcbs).
However the devices for each circuit must be grouped / labelled to show the association between them [2.9.5.2].

The only case where linking is mandated is for common-neutral final subcircuits [2.2.1.2].

Does that apply to RCD's as well Alec?

[AlecK]

RCDs need to be in a single body in order to function correctly.
They are always multi-pole devices, due to the need to have all live conductors of the circuit passing through the sensing toroid.
They are not assembled by linking several separate single-pole devices; as for overcurrent devices.

So if using RCBO as the circuit protection device, it will always be linked;
but that's nothing to do with the over-current function and solely because the RCD function can only happen in a single body.

[medistat]

Yep understand that. So will put in 3phase RCD for the 3phase sockets but 3 separates for the single phase sockets.