RCBO for solar

[karmannmann]

Hi looking for advice on fitting a 16 amp rcbo on a board for a solar pv is this okay?

 

[dansk]

Depends if the inverter has electrical seperation i.e transformer or not, and if its transformerless does it have a device to seprate the DC from the AC as some inverters do.

 

[karmannmann]

Its a sunnyboy 2500 but it was more of a standard q do inverters like rcbos or the other way around

 

[dansk]

ok - Sunnyboy should be fine on RCBO - ive not come accross any problems yet. FYI in the future, if you not aware, some inverters require "CLASS B" RCD's, dont confuse this with Type B.

But to answer your general q, yes inverters are ok on RCD.

 

[karmannmann]

Thanks for that youve been very helpful.

 

[saint]

I have just installed a 16A 30mA RCBO on a SB2500 inverter. The client has called to say its tripping. I would have used a 16A MCB but the system is TT and i couldn't achieve the max Zs for an mcb. Seems the inverter is causing the RCBO to trip.
Can anyone advise how i can sort this problem and still comply with BS7671?

 

[dansk]

If its a TT system it may have a 30ma RCD as the incomer, if thats the case then use the MCB, the Zs will go out of the window because the Ze will be high, but as its TT there not much else you can do.

If its got an RCD incomer remove the RCBO.

 

[saint]

No RCD incomer. Its a 16th Ed split load. But all the ways on the protected side where full.
If i just replace the RCBO for a MCB on the non protected side, will this comply?

 

[dansk]

Nope unless the radial to the invertor is mechanicaly protected.

It could be something to do with the RCBO - i have heard "proteus" RCBO trip for some reason - for a test why dont you take out a circuit on the RCD side, connect the PV up and try, if its ok then you know its the RCBO and you will then need to make it a permanent home on the RCD side.

 

[saint]

Sorry, i meant does it comply in terms of disconnection times etc. The cables is not buried and doesn't require mechanical protection either.

 

[dansk]

If its on the RCD side yes, allthough the Zs will be higher because of the Earth Spike, im not an expert on TT systems, so if anyone else would like to add to this.

Your using the 30ma for the disconnection time.

 

[SolarCity]

ALL cables need mechanical protection. The PVC covering of a twin and earth cable is the mechanical protection. If your cable isn't buried in any walls etc. then you don't need the RCD. If you're struggling for space, why not install a seperate CU?

You need a certain class of RCD for solar arrays (I forget what class this is - I simply avoid the need for it as it's far too problematic)

 

[yellowvanman]

If you put an MCB protecting a circuit on a TT system without an RCD it will not comply for disconnection times, doesn't matter if its SWA or anything like that.

eg. 16A MCB (Type B) needs 80A to trip within 0.4secs
To get 80A to flow Zs must be less than 3 Ohms (approx), Ze for a TT system is unlikely to be less than 3 Ohms.

 

[saint]

Gotcha
Will change the main switch on the split load CU for 100mA and change the 16a 30mA rcbo for a 16A mcb. I think that should cover me and not cause any trip.

 

[mmccx]

PV circuits cannot be protected by an RCBO, manufacturers recommend they are not used in PV circuits as they do not work as intended with current flowing the wrong way through it. You will need to install a separate dist board with a 30ma RCD main switch and then put the pv circuit on an mcb