RCBOs and voltage free relays

We have a smallish CBUS install in our home (UK) and looking to extend with garden lighting.

On the input side of our existing CBUS output units we have MCBs only and no RCBOs (one MCB for each relay/dimmer).

For our garden lighting I plan to add an aditional relay unit. My question is whether you could have an RCBO on the input side; there will be 8 circuits with GU10 LEDs on each channel therefore I intended to have a 6A RCBO on the input. We would then use MCBs on the output channels and this would reduce the overall cost.

Looking at the CBUS doc it states only MCBs on the input/output side and what confuses me more is that this applies to dimmer units only and not relays.

Any help would be gratefully appreciated.

Thanks

 

The main thing to remember is that MCB's are there to protect the wiring and RCD's are there to protect you. RCBO's just combine the two functions into a single unit.

Having an RCBO on the input-side to the relay unit is fine, but since you're already planning to only use a 6A RCBO, the MCB's on the individual channels are going to be a bit superfluous, unless they're really small MCB's (1-2A). Some countries do require an MCB per-channel and I can't remember what the case is for the UK.

I'm a little surprised to hear that you don't already have RCD protection on your other C-Bus circuits. It's certainly the case here in Australia that lighting circuits must be RCB protected.

There's certainly no issue with connecting RCDs/RCBOs to C-Bus products.

 

I just want to pass on something from a previous mistake of mine.
You dont want to lose power to the CBus relay or dimmer power suppply when a load trips the RCD.
Since a loss of power supply unit could stop the whole CBus network.
eg it needs it's own MCB.