Solar panel circuit MCB size?

[davesparks]

Thinking about it I've been guilty of the 'get the SDS out and give it some proper welly' approach when encountering resistance whilst drilling a hole. I wouldn't be surprised if most of us are!

 

[Gavin A]

besides, with the inverter off, even transformerless inverter circuits become protected by dint of being electrically separated.

Switch it back on and the insulation resistance test on start up should detect a damaged cable and not start up, so the circuit stays electrically separated until the fault's repaired.

At the end of the day, it's allowed under BS7671, and it's allowed because it's considered to be safe.

 

[Leesparkykent]

Thinking about it I've been guilty of the 'get the SDS out and give it some proper welly' approach when encountering resistance whilst drilling a hole. I wouldn't be surprised if most of us are!

exactly this is my point, it has been known lol

 

[Leesparkykent]

besides, with the inverter off, even transformerless inverter circuits become protected by dint of being electrically separated.

Switch it back on and the insulation resistance test on start up should detect a damaged cable and not start up, so the circuit stays electrically separated until the fault's repaired.

At the end of the day, it's allowed under BS7671, and it's allowed because it's considered to be safe.

and that is why i said IMO

 

[shanky887614]

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

 

[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.