Discuss Shared circuit for Solar PV & Outbuilding. in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Reaction score
26
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.
Shared circuit for Solar PV & Outbuilding. IMG_0350 - EletriciansForums.net Shared circuit for Solar PV & Outbuilding. IMG_0351 - EletriciansForums.net
 
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.
 
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.
 
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
 
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.
 
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
 
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.
 
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.

Not good. Thing is though, if the Solar PV is on it's own circuit protected by it's MCB and/or additional protection from a RCD then disconnection ( from mains) will occur within 40mS for earth leakage or 400mS on earth fault or short circuit.
But as you say, the solar PV will continue output for up to 5 seconds feeding the live conductors leaving the inverter and earth path fault via person or metallic object.
And because the protective earth conductor is connected to the MET then all exposed and extraneous parts will be live for that duration until the generator shutdown.
Surely the inverter should shutdown within 400mS as is the regulation for all final circuits under 32A.
 
Not good. Thing is though, if the Solar PV is on it's own circuit protected by it's MCB and/or additional protection from a RCD then disconnection ( from mains) will occur within 40mS for earth leakage or 400mS on earth fault or short circuit.
But as you say, the solar PV will continue output for up to 5 seconds feeding the live conductors leaving the inverter and earth path fault via person or metallic object.
And because the protective earth conductor is connected to the MET then all exposed and extraneous parts will be live for that duration until the generator shutdown.
Surely the inverter should shutdown within 400mS as is the regulation for all final circuits under 32A.

As far as I know a solar PV circuit can't be effectively protected by an RCD for this very reason and so the circuit must be installed in such a way that it does not require RCD protection.

Under short circuit conditions I would expect the inverter to have protection in place to disconnect a lot faster than 5 seconds, or failing that it wouldn't be physically capable of delivering fault current through a short circuit and the electronics will fail long before the 5 second mark.
 
I would not connect the PV system to the same supply!
you could safely isolate the AC isolator at consumer unit but the system is still a generator & will not be isolated completely, DC side will still be live & going into the micro inverter & although the micro inverter requires AC power to wake up & start letting voltage through what could happen under fault conditions?
you will not have safely isolated the whole system if you needed to work on the shed end.
 
As far as I know a solar PV circuit can't be effectively protected by an RCD for this very reason and so the circuit must be installed in such a way that it does not require RCD protection.

Under short circuit conditions I would expect the inverter to have protection in place to disconnect a lot faster than 5 seconds, or failing that it wouldn't be physically capable of delivering fault current through a short circuit and the electronics will fail long before the 5 second mark.
Thanks for the feedback Dave.
 
Back to the OP........... so it looks like "mycontribution.co.uk" were the last people to touch the CU - so why no label for the PV circuit and why did they leave the CU with covers missing?
 

Reply to Shared circuit for Solar PV & Outbuilding. in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock