Solar panel circuit MCB size?

[BruceB]

Wow, this thread took off a bit.

Personally I would be happy with dc cables running through my house properly protected/signed and prefer to have the inverter sited in a cool, convenient position rather than say in the loft.

If a customer still managed to drill into them, then put it down to Darwin's theories being played out.

Returning to the original topic as per the title, then for example the Schneider guidance is that when multiple mcbs are in a small enclosure then a 20% reduction in rating should be applied to determine the maximum service current. So for sustained operation at 16A, you should use a 20A mcb. In a hot environment the reduction increases.
http://www.schneider-electric.co.uk.../en/local/rti-catalogue-sections/SE7860_8.pdf
page 8/3

 

[driverman]

Not that I'm into design as such, but I can remember reading somewhere that MCB's should be down-rated if mounted sideways on within an enclosure. Also it makes sense not to put heavily loaded MCB's / fuses side by side. I've grown up with Wylex Boards whereby it was always the standard heaviest load near to the main switch then decreasing sizes away from the switch.

 

[driverman]

OK to re-capp. MCB side of things OK. Generally, are you guys OK with Solar Panel circuits being protected with 30Ma RCD's? One person on here said it was not an issue although he had changed a couple re nuisance tripping. Another said his company never install them. Thanks

 

[Richo77]

Yes solar PV should be protected by an RCD. Some manufacturers state 30Ma some state 100Ma. The solar array is outside, usually roof mounted so it requires RCD protection. I always install a new 2 way RCD board separate from the domestic CU to avoid nuisance tripping. The PV installation can have quite a lot of earth leakage and if it's connected to the same RCD as the house it can cause problems. Separating the two installations can make life a lot easier with regard to nuisance tripping.

 

[Gavin A]

Yes solar PV should be protected by an RCD. Some manufacturers state 30Ma some state 100Ma. The solar array is outside, usually roof mounted so it requires RCD protection. I always install a new 2 way RCD board separate from the domestic CU to avoid nuisance tripping. The PV installation can have quite a lot of earth leakage and if it's connected to the same RCD as the house it can cause problems. Separating the two installations can make life a lot easier with regard to nuisance tripping.

no it doesn't require an RCD.

The inverter manufacturers give specifications for RCD fitting where required by local regulations - ie where required by BS7671, so an RCD is only needed where it's required under BS7671.

All you're doing is adding a source of nuisance tripping to the system by adding an RCD where it's not needed.

 

[driverman]

no it doesn't require an RCD.

The inverter manufacturers give specifications for RCD fitting where required by local regulations - ie where required by BS7671, so an RCD is only needed where it's required under BS7671.

All you're doing is adding a source of nuisance tripping to the system by adding an RCD where it's not needed.

Thanks Gavin, To comply with BS7671 though, if the solar panel circuit is wired pvc t+e cable and buried within the plasterwork (less than 50mm) it must be protected by a 30Ma RCD. As far as I can see, no choice in the matter. Are ALL your LV circuits wired on the surface? Thanks

 

[Richo77]

I think you will find outside is a special location that requires RCD protection. All manufactures instructions on systems I have fitted have stated it requires RCD protection. Also I said I install a seperate board for PV with its own RCD, to prevent nuisance tripping on the domestic circuits. The MCS guy also confirmed that a RCD is a requirement on my annual inspections

 

[driverman]

Yes solar PV should be protected by an RCD. Some manufacturers state 30Ma some state 100Ma. The solar array is outside, usually roof mounted so it requires RCD protection. I always install a new 2 way RCD board separate from the domestic CU to avoid nuisance tripping. The PV installation can have quite a lot of earth leakage and if it's connected to the same RCD as the house it can cause problems. Separating the two installations can make life a lot easier with regard to nuisance tripping.

Thanks Rico, what I was planning was that the Solar panel circuit be wired on its own RCBO circuit, which is basically what you have been doing. I'm not into solar panel wiring, this is just a one off. Why do you install a 2 way unit? Thanks

 

[Richo77]

I install a 2 way board for the PV so the combined earth leakage from the house and PV doesn't cause problems. I cut the tails and put Henley blocks on them. This way my house CU and PV CU are separate. So the earth leakage from the house and PV doesn't combine to trip RCD's. The PV earth leakage can be quite high so i tend to put that on its own RCD as recommended in the manufactures instructions. I have been called out to lots of installations that are tripping because they have not been installed this way. I change it to this method and all is solved. Easier for testing too.

 

[driverman]

I install a 2 way board for the PV so the combined earth leakage from the house and PV doesn't cause problems. I cut the tails and put Henley blocks on them. This way my house CU and PV CU are separate. So the earth leakage from the house and PV doesn't combine to trip RCD's. The PV earth leakage can be quite high so i tend to put that on its own RCD as recommended in the manufactures instructions. I have been called out to lots of installations that are tripping because they have not been installed this way. I change it to this method and all is solved. Easier for testing too.

Yes, I understand your thinking hence I've gone separate RCBO's for each circuit. Just wondering why you put a 2 way unit in. Do you mean that the RCD + MCB takes the 2 ways up? Or you require 2 x circuits for your systems?

 

[Gavin A]

I think you will find outside is a special location that requires RCD protection. All manufactures instructions on systems I have fitted have stated it requires RCD protection. Also I said I install a seperate board for PV with its own RCD, to prevent nuisance tripping on the domestic circuits. The MCS guy also confirmed that a RCD is a requirement on my annual inspections

I think you'll find that the outside bit is DC, and your RCD has nothing to do with that side of the inverter - the RCD wouldn't trip if there were a fault on the DC circuit, how could it?

The inverters are either galvanically isolated, or transformerless with an integral RCMU unit to protect them.

what the MCS guy said says more about the substandard nature of the MCS inspection system than it does the reality of what's required.

 

[Richo77]

Just one circuit mate. Yeah RCBO would be fine

 

[Gavin A]

Thanks Gavin, To comply with BS7671 though, if the solar panel circuit is wired pvc t+e cable and buried within the plasterwork (less than 50mm) it must be protected by a 30Ma RCD. As far as I can see, no choice in the matter. Are ALL your LV circuits wired on the surface? Thanks

or use earthed metal capping, but yes an RCD would be one way of protecting the circuit in that situation.

If the inverter is in the loft we mainly run SWA surface mounted externally in retrofit installations to avoid disturbing the internal decor, having to pull carpets up etc.

 

[HandySparks]

I think you will find outside is a special location that requires RCD protection.

I don't think you will.

'Outside' in general isn't a special location or installation. Some specific situations, such as swimming pools, agricultural, etc. are.

In a normal domestic situation, it's only socket outlets outside that require RCD protection, not distribution circuits, lighting, etc.

 

[shanky887614]

I think you'll find that the outside bit is DC, and your RCD has nothing to do with that side of the inverter - the RCD wouldn't trip if there were a fault on the DC circuit, how could it?

The inverters are either galvanically isolated, or transformerless with an integral RCMU unit to protect them.

what the MCS guy said says more about the substandard nature of the MCS inspection system than it does the reality of what's required.

yup, ive seen 700v on some strings on bigger solar panel jobs.

only a positive and negative from solar panels so no where to connect an earth after the inverter anyway

we are talking multiple TP inverters in one room here