Shared circuit for Solar PV & Outbuilding.

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Shared circuit for Solar PV & Outbuilding.

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

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Marcus John

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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.
IMG_0350.jpg IMG_0351.jpg
 
Murdoch said:
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
Click to expand...
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.
 
bill01803 said:
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
Click to expand...
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
 
Marcus John said:
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.
Click to expand...

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.
 
davesparks said:
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.
Click to expand...

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.
 
Marcus John said:
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.
Click to expand...

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.
 
davesparks said:
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.
Click to expand...
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?
 
marc8 said:
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.
Click to expand...
We've been in touch with the electrician who installed the Solar PV and he was aware of the 6mm2 circuit which had been installed from the consumer unit to the weatherproof enclosure on the external wall for the provision of supplying future shed.
As you know, he used this 6mm2 circuit to route generated power back to the consumer unit via the 20Amp MCB (shared RCD).
So when asked by my sister what would be the arrangements for supplying the shed off this circuit , he suggested that he'd install a main isolator switch and suitably rated MCB for the 6mm2 SWA for the shed inside the weatherproof enclosure.
So it would appear the intention is to share the 6mm2 FTE circuit with shed supply and Solar feed.
Like I said earlier, my involvement is just installing a mini consumer unit in the shed, connect 6mm2 SWA at shed, run a 6Amp lighting circuit and a 20Amp radial power circuit. Carry out all the dead tests.
Verification of my work, connection to supply and live testing will be performed by a qualified electrician.
 
Marcus John said:
We've been in touch with the electrician who installed the Solar PV and he was aware of the 6mm2 circuit which had been installed from the consumer unit to the weatherproof enclosure on the external wall for the provision of supplying future shed.
As you know, he used this 6mm2 circuit to route generated power back to the consumer unit via the 20Amp MCB (shared RCD).
So when asked by my sister what would be the arrangements for supplying the shed off this circuit , he suggested that he'd install a main isolator switch and suitably rated MCB for the 6mm2 SWA for the shed inside the weatherproof enclosure.
So it would appear the intention is to share the 6mm2 FTE circuit with shed supply and Solar feed.
Like I said earlier, my involvement is just installing a mini consumer unit in the shed, connect 6mm2 SWA at shed, run a 6Amp lighting circuit and a 20Amp radial power circuit. Carry out all the dead tests.
Verification of my work, connection to supply and live testing will be performed by a qualified electrician.
Click to expand...
I would be very careful unless you put a warning notice at main consumer unit, who would know about this connection outside in waterproof box. How far away is the consumer unit can you not just run back to that location & leave the solar as it is or is to far away ?
 
Marcus John said:
Like I said earlier, my involvement is just installing a mini consumer unit in the shed, connect 6mm2 SWA at shed, run a 6Amp lighting circuit and a 20Amp radial power circuit. Carry out all the dead tests.
Verification of my work, connection to supply and live testing will be performed by a qualified electrician.
Click to expand...

If this is the case why are you wasting your time on here? Best you ask the spark you believe will sign off your work............. and presumably the Part P too
 
Marcus John said:
We've been in touch with the electrician who installed the Solar PV and he was aware of the 6mm2 circuit which had been installed from the consumer unit to the weatherproof enclosure on the external wall for the provision of supplying future shed.
As you know, he used this 6mm2 circuit to route generated power back to the consumer unit via the 20Amp MCB (shared RCD).
So when asked by my sister what would be the arrangements for supplying the shed off this circuit , he suggested that he'd install a main isolator switch and suitably rated MCB for the 6mm2 SWA for the shed inside the weatherproof enclosure.
So it would appear the intention is to share the 6mm2 FTE circuit with shed supply and Solar feed.
Like I said earlier, my involvement is just installing a mini consumer unit in the shed, connect 6mm2 SWA at shed, run a 6Amp lighting circuit and a 20Amp radial power circuit. Carry out all the dead tests.
Verification of my work, connection to supply and live testing will be performed by a qualified electrician.
Click to expand...

So ask the electrician who will be signing it off, we can't read their mind and tell you what they will want to see.
Although I would be concerned if they don't see the obvious flaw in the plan, there will be a discrimination issue that could lead to the aforementioned situation of the inverter happily killing a person.

Don't worry though, you will get away with it just like everyone else does, unless of course someone dies in which case you you'll be off to jail, do not pass go etc etc
 
marc8 said:
I would be very careful unless you put a warning notice at main consumer unit, who would know about this connection outside in waterproof box. How far away is the consumer unit can you not just run back to that location & leave the solar as it is or is to far away ?
Click to expand...
Hi Marc, as you say the safest, best practise method would be separate circuits but the guy who installed the Solar PV robbed the circuit that was intended for the outside shed. He tapped into the weatherproof enclosure which had 6mm2 FTE from consumer to 6mm2 SWA routed to shed. The two ends were obviously just coiled up for future connection.
My sister paid the builder during the initial first fix, an extra £800 to run a circuit from consumer to outside shed for future use. Now she's had her shed built some months after the Solar PV install we opened up the weatherproof enclosure and hello what's going on here?
So she calls this guy up and he says, oh yes that's fine I knew that cable was there for the shed and you can share it with the Solar PV.
Alarm bells started ringing in my head and that's why I turned to this board for some advice.
Personally I think he was pulling a fast one and to save himself routing a new circuit through the house, lifting floor boards, chasing out walls etc he just took the easy option.
 
Murdoch said:
If this is the case why are you wasting your time on here? Best you ask the spark you believe will sign off your work............. and presumably the Part P too
Click to expand...
I'm on here because I've identified a potentially unsafe condition and care about the health and well being of my sister.
What confidence do have in an electrician who says 'oh yeah that's fine mate, you can share your shed supply with the Solar PV circuit, no bovver'.
And even if he did sign it off, that doesn't make it safe.
I'm on here because I value the opinions of the experienced members.
I gotta say Murdoch, your responses have all had a tone of negativity in them. I'm sure you're a great electrician but you come across arrogant.
 
davesparks said:
So ask the electrician who will be signing it off, we can't read their mind and tell you what they will want to see.
Although I would be concerned if they don't see the obvious flaw in the plan, there will be a discrimination issue that could lead to the aforementioned situation of the inverter happily killing a person.

Don't worry though, you will get away with it just like everyone else does, unless of course someone dies in which case you you'll be off to jail, do not pass go etc etc
Click to expand...
I will get away with it? Are you suggesting i'm the one who will be energising this circuit? When I do reach the required competency to sign off my own work, I certainly would not be signing off a piece of crap circuit design that the one I've witnessed.
I'm well aware of the dangerous situation unfolding here and that's why I turned to the forum for advise.
 
So you sister paid £800 for a sub main for a shed - that if true is a complete rip off.

Arrogant, no. Trying to educate DIYers yes, but some simply don't want to hear what the facts are..... I never sign off another person's work.... It's as simple as that.

Given your last post are you training to be a spark?
 
Murdoch said:
So you sister paid £800 for a sub main for a shed - that if true is a complete rip off.

Arrogant, no. Trying to educate DIYers yes, but some simply don't want to hear what the facts are..... I never sign off another person's work.... It's as simple as that.

Given your last post are you training to be a spark?
Click to expand...
Yes i agree. During the first fix stage she asked her builder for a shed supply for future shed. So he added a 6mm2 FTE distribution circuit from fuse board to an external weatherproof enclosure, about 6 metres,then running from the enclosure to a location 10 metres away, 6mm2 SWA buried - £800
I'm not a DIYer in any electrical work. I'm in training to become a spark.
I've just completed 2 year EAL Diploma Level 2 and will be returning to college in September for 1 year EAL Diploma Level 3 and IET Wiring Regulations.
After that not sure what happens but i'm enjoying it so far.
 
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