Pv on rcd

[davesparks]

Hmmm I see.

what would you do? I can't say as I know really.

Install the PV circuit in such a way that it does not require RCD protection as an RCD will not provide protection to the circuit.

 

[uksparks]

Are you saying just put it on an MCB?

 

[uksparks]

Surely having an RCBO on it is going to be better than just having an MCB?

 

[davesparks]

Surely having an RCBO on it is going to be better than just having an MCB?

Not if the rcbo doesn't provide any protection. I would say that fitting rcbo protection would be worse than an MCB as it would make it appear to have RCD protection when in fact it won't work, plus of course it makes the person who installed it look like they don't know what they are doing and don't understand what they are doing.

The rcbo will detect a 30mA electric shock and disconnect within 300mS which could save someone's life, except the inverter will continue to supply power into that person for up to 5 seconds, ensuring that they are well and truly dead.

 

[Leesparkykent]

So I would be right in thinking that an RCD won't provide protection to the typical PV circuit you see in domestic installs.

Hmm its food for thought...i think you are right. Do you think (iv) of 551.7.2 should apply?

 

[davesparks]

Hmm its food for thought...i think you are right. Do you think (iv) of 551.7.2 should apply?

I'm pretty sure the whole of 551.7.2 applies,

 

[Leesparkykent]

And in the case of uksparks post then 551.7.1 would also apply so the RCBO would have to be double pole or SPSN.

 

[Deleted member 26818]

Lol, why should the PV supply disconnect in the event of a RCD tripping, and how will the PV power bypass the tripped RCD?

 

[davesparks]

Lol, why should the PV supply disconnect in the event of a RCD tripping, and how will the PV power bypass the tripped RCD?

Two possible situations:
1: PV shares a common RCD with a socket circuit (it's on a normal RCD protects way in a split board). A person using a portable appliance which goes faulty receives a shock, the RCD detects imbalance and disconnects within 300mS. Ordinarily the power goes off and the person stops getting a shock, but since there is a second source of power connected to the load side of the RCD (the PV) the electric shock continues until that source of supply is disconnected (up to 5 seconds) thus making death far more likely.

2: RCBO protection is provided the the PV circuit due to the cable buried in the wall requiring 30mA RCD protection. The reasoning behind the requirement for an RCD in this scenario is that a person damaging the unseen cable may receive an electric shock, maybe a person holding a nail and banging it in to hang a picture on. Pretty much the same sequence of events as above occurs, with the RCD disconnecting quick enough to save the persons life but the PV continuing to deliver the electric shock and quite probably killing the person.

The above obviously assumes that the person is completely healthy and meets the scientific model of a human which the 30mA 300mS rules are based on.

 

[SolarCity]

So I would be right in thinking that an RCD won't provide protection to the typical PV circuit you see in domestic installs.

That's how I've always understood it. I remember suggesting an RCD at the 'PV' end of the install (assuming that it's cable run required it) on here a few years ago but can't remember what the general consensus was.

 

[uksparks]

That's how I've always understood it. I remember suggesting an RCD at the 'PV' end of the install (assuming that it's cable run required it) on here a few years ago but can't remember what the general consensus was.

That would work would it not?

 

[Worcester]

That would work would it not?

Well not quite ...

You'd need one both ends, and the grid supply end would need to be time delayed, as you want the the Inverter end one to trip first and then the grid end one.

If you only have one at the inverter end, the cable would still be 'live' to the grid'
If the grid end one isn't time delayed, then you can't guarantee to trip the inverter one first, and if you don't it would still be powered by the inverter.

Hence why we design out the requirement

 

[gnselectricals]

So do I slate it or not [emoji3]

 

[Deleted member 26818]

Why would the PV supply be connected to the load side of an RCD?
PV is a secondary supply and should be connected at or very near to the origin of the installation.

 

[gnselectricals]

Why would the PV supply be connected to the load side of an RCD?
PV is a secondary supply and should be connected at or very near to the origin of the installation.

That's how's it's installed either mistakenly to offer Rcd protection or couldn't be bothered to fit an additional board and earth rods to get the Ra acceptable I imagine