Shared circuit for Solar PV & Outbuilding.

[Marcus John]

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.

 

[davesparks]

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.

 

[marc8]

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.

 

[Marcus John]

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.

 

[Octopus]

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?

 

[Marcus John]

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.

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.

 

[marc8]

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.

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 ?

 

[Octopus]

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.

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

 

[davesparks]

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.

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

 

[Marcus John]

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 ?

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.

 

[Marcus John]

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

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.

 

[Marcus John]

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

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.

 

[Octopus]

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?

 

[Marcus John]

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?

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.

 

[Octopus]

^^ why would a spark add a new circuit of twin and earth and then swa? Madness