Rcbo

DaveyD · Jan 22, 2014

Hi everyone.
Im an electrician but I don't install PV

I am doing some works and changing a cu.

The customer already has pv fitted. There is no room to add a separate board and they have put a 16a mcb on the rcd side if the 16th edition board. TNC-S earthing arrangement. The cable is buried in the wall so it will need 30mA rcd protection.
They made a mess actually. Took the 16a mcb from the immersion heater circuit and put that 2.5 t&e in with the cooker on that 32a mcb and also nothing was re labeled on the cu.
Anyway. I've read that you should not share an rcd with pv because under fault on another circuit the rcd will trip and yet the back feed from the pv will keep the busbar live for up to 5seconds while it shuts down.
I've also read that you can't use a seperate RCBO even if its on its own bar as they down like to be back fed.
I'm assuming that it will work on a standard Ac rcd as it was working on the old one its on.

So without adding a separate board is there any way I can get this all on a split load board?
Tia

Gavin A · Jan 22, 2014

what's the inverter?

sma, power-one will usually be ok to back feed a standard Type A RCBO, others may inject too much DC current and need a Type B to cope with higher levels of DC injection.

But I'm not sure how you intend to fit this to a standard split load board, as don't they usually only have 2 neutral bars, so you'd be unbalancing the neutral going through the RCD. We'd usually use a high integrity board for this, but maybe you can adapt the board somehow to turn it into an effective high integrity board... ie with the PV not sharing a neutral bar with the RCD circuits.

DaveyD · Jan 22, 2014

Gavin A said:
what's the inverter?

sma, power-one will usually be ok to back feed a standard Type A RCBO, others may inject too much DC current and need a Type B to cope with higher levels of DC injection.

But I'm not sure how you intend to fit this to a standard split load board, as don't they usually only have 2 neutral bars, so you'd be unbalancing the neutral going through the RCD. We'd usually use a high integrity board for this, but maybe you can adapt the board somehow to turn it into an effective high integrity board... ie with the PV not sharing a neutral bar with the RCD circuits.

Thanks Gavin. Yes sorry it is a high integrity board. So a single rcbo can handle if the inverter is ok? I will check that tomorrow

SibertSolar · Jan 23, 2014

Would recommend you fit an all-pole RCBO if you do go down that road. A single small inverter, depending on type "might" be ok on a 30mA RCD but be wary of nuisance tripping (if transformerless) and/or trip-coil saturation, dependant on the type of residual current detection fitted (Type-A dual-pole RCBOs are available)