Shared circuit for Solar PV & Outbuilding.

[Marcus John]

My sister has just had a shed erected in the garden and I'm going to install the mini consumer unit and run two circuits. One power for sockets and one for lighting.
I'll do all the dead testing of the circuits and then i'll be getting my college lecturer mate, who is a member of a competent persons scheme to (check my work) and then connect the supply before carrying out the live tests together.
The supply cable had already been run by the guy who built the house ( new build) but I'm curious how it's all going come together.
So the dedicated circuit for the outbuilding appears to be shared with the Solar PV circuit.
Starting from the distribution board..... 20Amp MCB ---> 6mm2 FTE runs through house to external weatherproof enclosure. Inside enclosure on outer wall, there is a connector block which connects 6mm2 SWA to a Solar PV array of just 4 panels. I'm guessing this is approx. 1kW. The panels have integrated inverters so it's 230Vac at the connector block. Also in the enclosure is the start of the 6mm2 SWA for the outbuilding supply, coiled up.
I've not discussed this with my electrician friend yet but was just throwing it out there for discussion.

 

[Octopus]

Best get your mate round to establish what's going on..... We can only speculate.

But my guess is that the pv install has taken the planned shed install but I wouldn't double then up

 

[Marcus John]

Best get your mate round to establish what's going on..... We can only speculate.

But my guess is that the pv install has taken the planned shed install but I wouldn't double then up

Yes, the PV Installation occurred many months after the house was built so it does look like the installer found an easy route back to the consumer unit instead of running his own cable.

 

[Marcus John]

Within the constraints of current carrying capacity, can a circuit be shared with solar supply and load demand.

 

[Octopus]

I refer you back to my original reply

 

[Marcus John]

I refer you back to my original reply

I refer you back to my original reply

Dissapointing that she paid the builder extra to have that circuit run ready for the future outbuilding and now it's been hijacked and she'll have to pay to get a new one run. Such is life.

 

[Octopus]

Where is the isolator for the PV?

 

[Marcus John]

Where is the isolator for the PV?

The AC isolator is at the consumer unit. There is not a DC isolator that I can see. The solar panel have mini inverter modules.

 

[mattg4321]

Could do with a couple of blanks too!

 

[Octopus]

^^ and better labelling................

 

[shaun1]

I don't think it would be possible to share the circuit in this situation because the isolatior for the PV install would also isolate the garage (but leave it connected to the PV panels). I would imadgine the Isolator for the solar installation has to be at the supply origin? and so moving it is not an option.

 

[bill01803]

PV should not be on a RCD with other circuits because of it's shutdown time being up to 5 seconds, ie. rcd trips in under 40mS solar shut down up to 5S

 

[Marcus John]

PV should not be on a RCD with other circuits because of it's shutdown time being up to 5 seconds, ie. rcd trips in under 40mS solar shut down up to 5S

Forgive me for not understanding this fully as have only just passed my Level 2 last week.
Does this mean that if there was an earth leakage issue on any of the other final circuits sharing the RCD with the PV then after automatic disconnection of mains supply in up to 40mS there would still be a generated voltage coming from the solar PV ( if it was sunny) for a further 4.96 seconds until the inverter shuts down due to no power supply from mains.
So 230Vac will be present on all exposed and extraneous parts for the time the inverter is still on ( approx. 4.96s) because the earth fault loop has been interrupted because the RCD had tripped and blocking the fault current route back to the origin of earth fault.

 

[Octopus]

So to sum up:

You can't use the PV cable to supply the shed

The PV MCB should not be on a rcd with other circuits...

Have fun with the floor boards

 

[davesparks]

Forgive me for not understanding this fully as have only just passed my Level 2 last week.
Does this mean that if there was an earth leakage issue on any of the other final circuits sharing the RCD with the PV then after automatic disconnection of mains supply in up to 40mS there would still be a generated voltage coming from the solar PV ( if it was sunny) for a further 4.96 seconds until the inverter shuts down due to no power supply from mains.
So 230Vac will be present on all exposed and extraneous parts for the time the inverter is still on ( approx. 4.96s) because the earth fault loop has been interrupted because the RCD had tripped and blocking the fault current route back to the origin of earth fault.

It means that if a person receives an electric shock the RCD will disconnect fast enough to prevent them dying, but the solar PV will continue to output voltage for up to 5 seconds, more than long enough to kill them and char-grill the body.