Question from a position of relative ignorance

[Octopus]

I posted a question a while back about my brother getting PV, and from the quote he's had so fa,r the justification certainly looks good, if not impressive.

He has an old BS 3036 board and will be asking me to install a new one ....

So my question is, what MCB rating would the PV "circuit" need? and is it OK to install on a dual RCD board or would members recommend a board with the PV circuit on a RCBO?

Thanks

 

[Gavin A]

it shouldn't be on a shared RCD with any other circuits.

other than that, follow 17th edition, but usually we use a 16amp MCB as it is only permitted to output as 16amps, despite the cable rating being much higher.

 

[Octopus]

it shouldn't be on a shared RCD with any other circuits.

other than that, follow 17th edition, but usually we use a 16amp MCB as it is only permitted to output as 16amps, despite the cable rating being much higher.

Interesting comment as all the PV systems I've encountered have been on dual RCD boards.

 

[DurhamSparky]

im changing a Cu on Wednesday in prep for a Rent a roof coming along shortly after... rent a roof CU change was £750 quid... lol

i am installing a Dual RCD with non protected 16A MCB which in turn goes to a FCU labeled SOLAR!

they can connect to the system that way!

 

[Octopus]

im changing a Cu on Wednesday in prep for a Rent a roof coming along shortly after... rent a roof CU change was £750 quid... lol

i am installing a Dual RCD with non protected 16A MCB which in turn goes to a FCU labeled SOLAR!

they can connect to the system that way!

Why the FCU?

 

[DurhamSparky]

so they don't mess with the nice shiney CU i am installing!

 

[Gavin A]

Interesting comment as all the PV systems I've encountered have been on dual RCD boards.

rcd trip time is 0.04 seconds, inverter anti-islanding protection trips out in up to 5 seconds.

also, inverters tend to have a leakage to earth of 5-10mA as well, so they will increase the risk of nuisance tripping if combined with household circuits that may also have slight earth leakages on them.

lots of companies do install to that side of the RCD, but that doesn't mean it's a good idea to be one of them.

 

[VMan]

rcd trip time is 0.04 seconds, inverter anti-islanding protection trips out in up to 5 seconds.

also, inverters tend to have a leakage to earth of 5-10mA as well, so they will increase the risk of nuisance tripping if combined with household circuits that may also have slight earth leakages on them.

lots of companies do install to that side of the RCD, but that doesn't mean it's a good idea to be one of them.

This is interesting and has been discussed many times before, but i have had a further thought into this..
..if the double pole RCD has tripped <0.4s and the Inverter still supplying the circuit with power for 5 seconds, which most agree, but the Earth Fault loop path is no longer to the transformer(as this had theroetically been disconnected), but back to the inverter itself.

With only 16Amps max current output from inverter(under g83), not the 600+ Amps you may get from a PME fault (as we established is now disconnected), and what would more than likely be a higher fault loop impedance path back to the inverter, what is the real volatge potential difference / Realistic Danger to the consumer in the even of an earth fault?? - i think would be quite low.

Any Branic put some equations to my logic? - not saying its right, just another view on it all!

What you guys think?? Make sense?

V

 

[Gavin A]

This is interesting and has been discussed many times before, but i have had a further thought into this..
..if the double pole RCD has tripped <0.4s and the Inverter still supplying the circuit with power for 5 seconds, which most agree, but the Earth Fault loop path is no longer to the transformer(as this had theroetically been disconnected), but back to the inverter itself.

With only 16Amps max current output from inverter(under g83), not the 600+ Amps you may get from a PME fault (as we established is now disconnected), and what would more than likely be a higher fault loop impedance path back to the inverter, what is the real volatge potential difference / Realistic Danger to the consumer in the even of an earth fault?? - i think would be quite low.

Any Branic put some equations to my logic? - not saying its right, just another view on it all!

What you guys think?? Make sense?

V

I don't know the answer to that, and last time I tried to work it out my head nearly exploded, but I think it depends really on what the fault is the causes the rcd to trip, and if that fault itself creats a path back to the inverter.

the nuisance tripping issue is the clincher though for me anyway, particularly with the TL inverters.

 

[moggy1968]

the other problem is that interference currents from some inverters may delay the RCD tripping or it may not trip at all, so making all the circuits on that RCD effectively unprotected.