The site surveyor

[kme]

Had been told that fitting a 20A MCB on a domestic 4KW solar install was unacceptable, he told me this morning.

So I asked why.

He went on to explain that, as the DNOs, under G83, limited your export level to "3.86KW" (which is apparently 16A??? 241.25V anybody?), they DEMANDED 16A MCBs were used to limit the export current.

I actually DID fall off the chair.

Then called the QS in from the next room, and got the guy to repeat what he`d been told. When we explained to him, with the help of the time/current curves, that a B16 would carry 20A without a concern, he was really confused.

We had to break it to him (gently) that the inverter is told what spec. it has to work to, and IT will limit the output current. Plus, a 4KW peak system, giving 80% max eff. is only going to produce 3200W.........so it`ll never get to 16A

Thinking about this later; I`m wondering if it is worth / allowed, to have a 5KW peak array; 20% losses drop you back to 4KW, allowing you to approach your maximum feed-in?

It is constantly amazing how many people don`t know the stuff they should know about the kit

 

[steptoe]

ah,

I had something similar,

20A MCB (the kit I was supplied with!)

and got pulled as to why it wasnt a 16A, well it was pretty obvious the guy pulling me was clueless, so instead of dazzling him with my natural brilliance,

I baffled him with my usual BS, :slap

TBH I coulda told him anything and just threw in a few big made up words and he woulda believed it.!

interesting point about if you are allowed to include the in-efficiencies though, somehow I doubt it,,,,,

 

[kme]

Ooh!

I need to have a good re-read through G83.....and finish G59......we`ve got some 10KW+ stuff coming up, and other than the QS and myself, I think all the other guys are part P only - not surprising at approx

 

[binky]

Some time a go a company was advertising 5kWp systems, no doubt based on inefficiencies. Didn't last long. FiT is based on kWp not allowing for inefficiency, and ultimately roof size and 16A is the limit.

---------- Post Auto-Merged at 11:04 ---------- Previous post was made at 11:01 ----------

Had been told that fitting a 20A MCB on a domestic 4KW solar install was unacceptable, he told me this morning.So I asked why.

He went on to explain that, as the DNOs, under G83, limited your export level to "3.86KW" (which is apparently 16A??? 241.25V anybody?), they DEMANDED 16A MCBs were used to limit the export current.

I actually DID fall off the chair.

Then called the QS in from the next room, and got the guy to repeat what he`d been told. When we explained to him, with the help of the time/current curves, that a B16 would carry 20A without a concern, he was really confused.

We had to break it to him (gently) that the inverter is told what spec. it has to work to, and IT will limit the output current. Plus, a 4KW peak system, giving 80% max eff. is only going to produce 3200W.........so it`ll never get to 16A

Thinking about this later; I`m wondering if it is worth / allowed, to have a 5KW peak array; 20% losses drop you back to 4KW, allowing you to approach your maximum feed-in?

It is constantly amazing how many people don`t know the stuff they should know about the kit

Just remineded me of a question - do MCBs work in reverse?? I've always assumed that as it is AC it doesn't really matter which way the leccy flows, but am I right in thinking that?

 

[kme]

Yes, for MCB`s.

Not RCDs with electronics though - and not RCBos

 

[m4tty]

I came across an mcb wired upside-down a few weeks ago and wondered if that was ok. It was tripping on overload so though it must be ok. Someone had added a shower onto an outbuilding feed as the house fuseboard was a bs3036 and the outbuilding feed was covered by 30mA rcd in single enclosure. They just shoved the shower feed into bottom on 32a mcb feeding outbuilding.

Is it ok to use an mcb to other way around?

 

[Sidewinder]

M4tty,

An mcb will work either way.

"SOME" stand alone RCD's will work either way, you need to check makers instructions.

I know the Wylex WRMT100/2 will work wired in either direction, I have been looking on line for the instructions but can't find them, I have a paper copy here if they turn up I'll try to post.

As far as RCBO's go they are directional.