Solar panel circuit MCB size?

[Leesparkykent]

why would the customer need to go into the loft to isolate it anyway.

if the inverter is in the loft just isolating the ac side will turn the inverter off.

the dc cables will always have potential on them unless the customer covers them on the roof or works at night lol

hes on about putting the inverter downstairs by the consumer unit

 

[shanky887614]

hes on about putting the inverter downstairs by the consumer unit

yes but doing it that way would need local isolation for dc side in the loft as well for the solar panels.

 

[Gavin A]

This is a graph of failure rates vs operating temperatures for capacitors - not solar inverter capacitors specifically, but indicates the problems associated with operating inverters in lofts as the issue is pretty much generic for all capacitors (though some cope better than others).

Fine if there's no other option, but causing your customer to have to fork out for a new inverter twice as often as they probably would have with the inverter in the garage where that was an option doesn't seem like a good idea to me.

 

[shanky887614]

This is a graph of failure rates vs operating temperatures for capacitors - not solar inverter capacitors specifically, but indicates the problems associated with operating inverters in lofts as the issue is pretty much generic for all capacitors (though some cope better than others).

Fine if there's no other option, but causing your customer to have to fork out for a new inverter twice as often as they probably would have with the inverter in the garage where that was an option doesn't seem like a good idea to me.

what capacitors were used in that test?

a lot of chinease caps are crap.

there is a reason good mid-high end psu in pc's use japanise capacitors becauae they last a lot longer.

i have had two cheap nasty power supplies fail on me from leaking capacitors

 

[Gavin A]

what capacitors were used in that test?

a lot of chinease caps are crap.

there is a reason good mid-high end psu in pc's use japanise capacitors becauae they last a lot longer.

i have had two cheap nasty power supplies fail on me from leaking capacitors

the capacitors themselves weren't anything like those used in inverters, much lower voltage units, but it was the best graph I could find to illustrate the point about the increase in failure rate / decrease in lifetime with higher operating temperatures.

This effect is fairly universal for capacitors although the specific lifespans for given temperatures will vary depending on type and quality.

Here's another.

 

[davesparks]

Even if you use the best components in the world to build something it will still last longer and work more efficiently if it is installed in a cooler environment

 

[Gavin A]

this is the source of the first graph

 

[shanky887614]

dont forget that is internal temperature and the internals will hit 30oC quite easily inside the inverter so i doubt it would make a huge difference, throw as many charts at me as you like

 

[Gavin A]

Even if you use the best components in the world to build something it will still last longer and work more efficiently if it is installed in a cooler environment

yep.

I expect the likes of a shade greener will be in for a very nasty surprise in coming years as they've installed every single inverter they've used in the loft, and used the cheapest possible inverters they could get hold of in bulk from china.

I'd lay odds that virtually all of their inverters will need replacing within 10 years.

Oh yeah, and they also use 2.5mm2 t&e cable on every job, and only install 3kWp systems upwards, then wonder why they have loads of issues with inverters tripping out for over voltage (after installing multiple systems on the same street without obtaining prior permission as well).

 

[Leesparkykent]

yep.

I expect the likes of a shade greener will be in for a very nasty surprise in coming years as they've installed every single inverter they've used in the loft, and used the cheapest possible inverters they could get hold of in bulk from china.

I'd lay odds that virtually all of their inverters will need replacing within 10 years.

Oh yeah, and they also use 2.5mm2 t&e cable on every job, and only install 3kWp systems upwards, then wonder why they have loads of issues with inverters tripping out for over voltage (after installing multiple systems on the same street without obtaining prior permission as well).

same as isis solar and home sun apart from a lot of these were fitted with fronius inverters.

 

[netblindpaul]

This forum never ceases to amaze at the lack of understanding of some members, and their total denial when it comes to absolute engineering and scientific facts, and proven data.

 

[shanky887614]

same as isis solar and home sun apart from a lot of these were fitted with fronius inverters.

i thought some of the fronius inverters came with a 15 year guarantee?

 

[Gavin A]

dont forget that is internal temperature and the internals will hit 30oC quite easily inside the inverter so i doubt it would make a huge difference, throw as many charts at me as you like

I know, but the rate of cooling is directly proportional to the ambient air temperature.

I also know that we get virtually every job where the other companies quoting have opted to install the inverter in the loft when there was a cooler option available after we explain this point to them, particularly when the customer is more technically literate.

 

[Leesparkykent]

i thought some of the fronius inverters came with a 15 year guarantee?

yea i think so

 

[Gavin A]

i thought some of the fronius inverters came with a 15 year guarantee?

Fronius offers a 5-year manufacturer warranty on all inverters as standard. You also have the option of extending the warranty period to 10, 15 or 20 years. If a claim is made, Fronius bears the costs for original replacement parts, transportation and work undertaken. The extended warranty therefore protects against any fluctuations in price for the entire warranty period. In addition, free support is on hand from our competent and easy to reach hotline team for the entire duration of the warranty period.

but extended to 10 years as of 1st January apparently

 

[davesparks]

dont forget that is internal temperature and the internals will hit 30oC quite easily inside the inverter so i doubt it would make a huge difference, throw as many charts at me as you like

If the ambient temperature is less then the cooling of the unit will be more efficient,

 

[Gavin A]

So to conclude, the only reason not to put the inverter in the garage is some personal preference based on some vague fear of permanently live dc cables despite them being mechanically protected, and protected as an electrically separated circuit, and via RCMU and start up insulation resistance tests by the inverter.

The reasons in favour of it are based on sound scientific and engineering principles.

Think I'll stick to our methods and reasoning tbh.

 

[shanky887614]

no fear of live cables in walls, i would just rather put it in the loft unless customers wants it else where, let the customer choose where they want it

 

[Leesparkykent]

i understand your point on mechanical protection. but you keep banging on about start up insulation tests etc,this is irrelevant as the dc cables will still be live before, during and after regardless if the inverter starts up or not due to the insulation resistance test carried out by the inverter

 

[shanky887614]

i understand your point on mechanical protection. but you keep banging on about start up insulation tests etc,this is irrelevant as the dc cables will still be live before, during and after regardless if the inverter starts up or not due to the insulation resistance test carried out by the inverter

what are you talking about?

the panels themselfs are always generating electricity the inverter only checks for supply on ac and switches dc accordingly

 

[Leesparkykent]

what are you talking about?

the panels themselfs are always generating electricity the inverter only checks for supply on ac and switches dc accordingly

im quoting Gavin A. and this is my point exactly, Panels are always producing under daylight hence cables will always be live to dc isolator

 

[shanky887614]

im quoting Gavin A

ah i didnt see a quote

 

[Leesparkykent]

ah i didnt see a quote

sorry mate should of quoted Gavins post #67

 

[Gavin A]

i understand your point on mechanical protection. but you keep banging on about start up insulation tests etc,this is irrelevant as the dc cables will still be live before, during and after regardless if the inverter starts up or not due to the insulation resistance test carried out by the inverter

not irrelevant as if the inverter doesn't start up, or cuts out, then even on a TL inverter the circuit stays / becomes an electrically separated circuit with no potential to earth, so even if the cables did somehow get damaged and exposed despite the mechanical protection it would only be dangerous if someone actually grabbed hold of both + and - exposed cables at the same time, and only life threatening if they were holding one bare wire in each hand. ie they could touch the positive or negative cable while also touching an earth bonded radiator and feel absolutely nothing.

It'd also alert the customer to the fault as the inverter wouldn't be working, and the inverter would be somewhere easily accessible for them to notice this.

 

[driverman]

Read thread with great interest after my original question, thanks very much. I did chat to the customer last night and the reason for the inverter sited downstairs was..... cooler position.....which some you of mentioned earlier. If inverter sited elsewhere in the modern home and away from the mains position then I would of thought most homes would have 30ma RCD protection. Does that have any impact on solar panel installations?

 

[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

 

[Leesparkykent]

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.

what has the RCD in your 2-way consumer unit got to do with the DC side of things= NOTHING lol

and i can probably rest assure you are not fitting type b RCD's as you dont have to!

 

[infinity]

Rihco what a load of tish! It does not require RCD protection at all, we always design the RCD out so surface mounted or alike then no nuisance tripping can occur. An inverter can cause nuisance tripping on its own RCD as well I've seen it, and changed it. RCDS with solar PV Is usually poor design Tbh

 

[Richo77]

I follow manufacturers instructions. And also the MCS inspectors have instructed us to it this way.

 

[Leesparkykent]

I follow manufacturers instructions. And also the MCS inspectors have instructed us to it this way.

Manufacturers instructions for the inverter or panel/dc cable/dc plugs?

 

[Gavin A]

I follow manufacturers instructions. And also the MCS inspectors have instructed us to it this way.

You've misread the instructions, and the MCS inspector doesn't know what he's talking about - many of them don't.

I had one attempting to insist that I should have earth bonded the array frame on an isolating transformer inverter system under the old rules about bonding the frames for TL inverters only. He was a former gas fitter who'd never installed a solar PV system.

 

[Gavin A]

If regulations in the country of installation stipulate an external residual current device, you must use
a device with a tripping threshold of 100 mA or more.

that's SMA's instructions relating to RCDs.

 

[SibertSolar]

omg....where's that popcorn smiley...

 

[infinity]

My MCS assessor last year was a plumber! No electrical quals or experience what so ever.
But he did know how to navigate a QMS manual

 

[Gavin A]

The head technical person from one of the MCS schemes rang me one time a while back because I'd had a pop at their assessors on here (if I remember right).

They were of the opinion that their assessors really knew what they were doing because they made sure they'd all done a minimum of 5 solar PV installations before they'd give them a job as an assessor.

IIRC I pointed out that our apprentice had done around 100 installs.

Boils my **** that they all consider it acceptable to have folk assessing us who we'd not class as competent to even supervise the most basic of domestic installs*.

Apparently this isn't something that can be discussed at MCS though, 'it's an enforcement issue'.



*not tarnishing all assessors with the same brush, there are some highly competent assessors out there as well, it's just the minimum standards that are set far too low.