PV system

[sparks1234]

We have been asked to move a PV system meter and isolator etc. I did speak to the original installer as we do not get involved in them normally.
There was a couple of things that surprised me though. The system was connected via an isolator, meter and MCB and the main henly block. When I mentioned to the guy that we were planning on burying the cable to the loft and mentioned RCD protection he said it was not necessary on a PV system. My thoughts are that the cable is buried and carrying 230 volts and is therefore harmfull.
Interseted to know your opinions.
Another thing that surprised me was they had used a 3 pole isolator and had taken live, neutral and earth through it.

 

[Engineer54]

Remember that the voltage is DC until it reaches the inverter panel!! Normally DC is protected against overload and short circuit by BS 88 fuses rather than MCBs. I have seen those MCBs that are rated for DC, trip for no apparent reason. Only a couple of months ago i changed a DP MCB on such a system for two fuse carriers, no more nuisance tripping...lol!!

Also remember that the PV panels can't be turned off so to speak, they generate continuously while they are receiving light.

No idea why the installer said no need to bury or not necessary to bury a PV cable, or why they have used a 3 pole isolator breaking the Earth path. I can only assume to completly isolate the PV array and it's frame!!

A couple of questions......What is the distance from the PV array to the inverter panel, a long run?? What protection or isolation is there as the PV supply cable leaves the PV array?? What sort of output are we talking about for this PV installation ...5KW??

 

[Superspark23]

My old company never put PV systems on an RCD it concerned me a fair bit, and im sure its not right, but the reason they done it was the pv system can interfer with the RCD causing it to trip, i don't know how true it is.

 

[sparks1234]

From what I can make out, the system does not produce anything if the house has no power, it requires 230 to allow the system to work. It really is this that I dont like as the cable going to the loft is going to be buried and they say it doesn't need RCD protection

 

[Engineer54]

From what I can make out, the system does not produce anything if the house has no power, it requires 230 to allow the system to work. It really is this that I dont like as the cable going to the loft is going to be buried and they say it doesn't need RCD protection

What do you mean, ''the system does not produce anything if the house has no power, it requires 230 to allow the system to work.'' ??? The system is generating power from the sun or let's say light source. Why does it need 230 volt power supply ???? You could in fact charge battery banks with a PV system.

If your talking about feeding back into the DNOs system, the inverter unit may be next to the CU/Meter point, the down cable from the PV array would then be at a DC voltage. No problem installing an RCD from the inverter to the DNOs supply...

What are we talking about here, when your talking about the cable being ''buried''??

 

[sparks1234]

Exactly what I said. If there were a power cut to the building then the PV system shuts itself down and does not produce any power to be fed back into the system or be used by the household.
The inverter unit (in this case) is located in the loft so the cable coming from the loft to the consumer unit position is therefore AC.
So thats why I was asking about the cable that is "burried" in the wall and not controlled through and RCD

 

[SMB]

Ah, I understand now.

That buried cable needs to be RCD protected if its buried 50mm or less within the wall (if your about to alter the circuit that is).

Regards.

 

[Engineer54]

OK, i'm with you now!! lol!! I basically can't see any problem installing an RCD after the Inverter unit, in fact that's what a friend of mines system has... I'll have to ask him what is at the other end where it feeds into the Suppliers incoming supply. His system is mounted on the roof of his showroom building that is rented out to BMW and a furniture supplier. So the incoming supplies, are in a locked electrical cupboard on the outside of the new building.

Found some photo's of his system, and included here....


This is his inverter layout....

As you can see here,....An RCD has been included in the inverter unit's AC output to the power supply company system.

The DP Breaker, is for a double weather-proof socket outlet on the roof. Nothing to do with the PV system.

 

[SMB]

If the invertor is positioned next to the cu then one double pole isolator is required for it next to the invertor.

If the invertor is in the loft then 2 double pole isolators are required, one next to the cu and one next to the invertor in the loft.

If the 230v cable running to the invertor is buried 50mm or less in the wall then it will require RCD protection.

 

[JulianC]

The AC cable on a PV system is not exempt from the regs. so, as mentioned above, if it needs an RCD due to being buried in a wall etc. then it needs an RCD. Fitted plenty of PV systems on RCDs and never had any spurious tripping issues.

Switching the cpc through the isolator is just plain wrong.