EICR - PV Install

[jibjob]

No, if the house is using 3kw and the system is producing 3kw it would use the pv, if the house is using 4kw and the pv is producing 3kw it would use 3kwpv and 1kw mains, if the house is using 1kw and the pv is producing 3kw the it would use 1kw pv and export 2kw pv back into the grid.

Hope that makes.

Ok, I was (mistakenly?) going by what the client told me. I've learnt alot of useful stuff this evening. At least now I can go back with the EICR completed with issues observed & recommendations on how to bring it all up to spec

 

[moggy1968]

I know that, my question was whether it actually has to be on it's own dedicated RCD on TT, or can be on the shared RCD.

My thoughts would be that it'd be ok on the shared RCD as it's only going to be around 10mA leakage current from the inverter, leaving a good 90mA spare for leakage currents from other circuits... though there is the issue that if it trips, it trips everything.

sorry Gavin, I wasn't sure which bit you were questioning, although I did answer both aspects in my post.
In view of the complexities of the arguments on shared RCDs I would be inclined to play it safe and put it on it's own dedicated RCD. It becomes part of the regs if it prevents the RCD tripping correctly but is not (as far as I am aware) specifically a part of the regs that PV must have it's own dedicated RCD.

 

[Gavin A]

But as the PV can take 5 seconds to shut down it could still be live on the "tripped" side of the RCD for those 5 seconds not the required 0.4.

but an RCD trips due to a live>earth fault (or neutral earth fault) somewhere on the circuit... where is the return path from earth to the inverter once the dual pole RCD has tripped?

If there's no return path to the inverter from earth, then there should be no danger from a live>earth fault.

At least that's how I've understood it.

 

[Earthstore]

My understanding is, an RCD trips because of an imbalance between live and neutral, so a live to earth could cause this,
IE man touches live cable, as he is earthed (unless he is flying) this would cause an imbalance between live and neutral so RCD trips therefore cutting off the live and neutral in 0.4 of a second so all is safe.

If PV is on a shared RCD then the same man would get the live from the PV for up to 5 seconds going through him to earth, it could also put the power into any fault for the 5 seconds.

I could be wrong, but this is my layman's understanding of it.

 

[moggy1968]

there is also some concern that interference currents induced by the PV could prevent the RCD from operating at all, but this is going over old ground. I'm not 100% convinced either way, which is why I wouldn't share an RCD.I would rather play it safe!

 

[BruceB]

But as the PV can take 5 seconds to shut down it could still be live on the "tripped" side of the RCD for those 5 seconds not the required 0.4.

Whilst that is true, as one of the sides of the inverter output is not referenced to earth then there would be no danger from that unless a second fault to earth was also present.

What we do not know is whether the fuse board drawn is actually a fuse board or say a 16th edition consumer unit. If it is the former then the rcd is probably 30mA and best not to share it as it will be providing the 40ms protection Earthstore refers to, although as we have discussed before the ESC BPG does allow it to be shared. If it is a 16th edition consumer unit already with 30mA rcd for socket circuits, then the rcd might be a 100mA or greater and be a time delayed one protecting for TT reasons. If it is that then I would not have a problem personally 'sharing' the rcd and leaving it as the single point of isolation.

The criminal point is that there is no overcurrent protection.

 

[SolarCity]

Whilst that is true, as one of the sides of the inverter output is not referenced to earth then there would be no danger from that unless a second fault to earth was also present.

Perhaps from a damaged cable on the roof that comes into contact with a bonded frame or extraneous roof structure?

On this subject, I've often pondered if there is any real danger to firefighters as the DC side of the inverter shouldn't be referenced to earth anyway.

 

[BruceB]

Perhaps from a damaged cable on the roof that comes into contact with a bonded frame or extraneous roof structure?

Yes, with a transformerless, but that should get picked up by the RCMU with most such inverters and already have tripped it out.

 

[jibjob]

Whilst that is true, as one of the sides of the inverter output is not referenced to earth then there would be no danger from that unless a second fault to earth was also present.

What we do not know is whether the fuse board drawn is actually a fuse board or say a 16th edition consumer unit. If it is the former then the rcd is probably 30mA and best not to share it as it will be providing the 40ms protection Earthstore refers to, although as we have discussed before the ESC BPG does allow it to be shared. If it is a 16th edition consumer unit already with 30mA rcd for socket circuits, then the rcd might be a 100mA or greater and be a time delayed one protecting for TT reasons. If it is that then I would not have a problem personally 'sharing' the rcd and leaving it as the single point of isolation.

The criminal point is that there is no overcurrent protection.

Tis a Wylex box with plug in retro fit BS 60898 MCB's. Standalone 30mA RCD upfront, which is shared with PV as shown in my drawing. RCD? maybe, maybe not, overcurrent/short circuit protection definately.

Thanks guys for all your help

 

[SolarCity]

The lack of overcurrent protection is jaw-dropping. I can't believe that an electrician could actually make such a fundamental error.

 

[jibjob]

The lack of overcurrent protection is jaw-dropping. I can't believe that an electrician could actually make such a fundamental error.

To be honest, doing what I do, lots of domestic testing & lots of maintenance, I come across it a fair bit, showers being the most popular one. Shower has been added to an existing install, with a 6 or 10 mm T&E straight out of the main switch terminals & thru a standalone 30mA RCD completely bypassing any form of OPD. Baffling

 

[sedgy34]

To the OP just test the ac side from the inverter, your not qualified to mess with the DC side (no offence)

 

[Gavin A]

To the OP just test the ac side from the inverter, your not qualified to mess with the DC side (no offence)

bit unnecessary that wasn't it?

The OP hasn't mentioned the DC side anyway, but would probably be better qualified than whichever twunt carried out the initial installation

 

[Gavin A]

To be honest, doing what I do, lots of domestic testing & lots of maintenance, I come across it a fair bit, showers being the most popular one. Shower has been added to an existing install, with a 6 or 10 mm T&E straight out of the main switch terminals & thru a standalone 30mA RCD completely bypassing any form of OPD. Baffling

probably mistaking the rating of the RCD for being the overcurrent trip value of the RCD... tbf it might be that the RCD will burn out before the cable, but that's not exactly a recognised method of over current protection

 

[sedgy34]

bit unnecessary that wasn't it?

The OP hasn't mentioned the DC side anyway, but would probably be better qualified than whichever twunt carried out the initial installation

I did say (no offence) it's fact