Cu & Pv Configuration

[trevor_clark]

Have been reading with interest forum relating to PV connection to CU. I have a 3.5Kw system installed witch is connected though the FIT meter to my 17th edition 10way duel RCD Volex CU to a 16A B MCB on the 63A 30mA RCD side of the board, no other circuits share the MCB. Prior to having the PV system install I planned to put a 6way RCD consumer unit in the garage fed by splitting the supply meter tails and installing a 40A mains switch for isolation purposes. I had run a 10mm T&E cable btw garage and house through floor joist voids for the feed.  I now find this would not be served by the PV so I would not benefit from the free electric for garage and shed. I could use a spare way in the house CU and fit a 40A MCB and the 10mm T&E but suspect I should not connect to another RCD CU. I wonder if I could split the cable on the CU side of the FIT meter not sure of the implications of doing this (can the FIT supply two CUs? I would appreciate and advice on this matter.

Thanks Trevor   

+

 

[Andy™]

where you circuit is fed from on your side of the meter isnt an issue, it would work properly connected to a spare MCB in the board, or from a mini CU and split meter tails.

but more importantly, solar PV should NOT be connected to a dual split load board where it shares an RCD with another circuit. if it is done this way, then demand the installers come back and do it properly and to wiring regulations

 

[ProDave]

Just to add to the above, it's because when someone gets a shock and the RCD trips, the Solar PV inverter will continue providing power for up to 5 seconds before it detects loss of grid connection and shuts down. By which time your poor victim is probably dead.

Sadly it seems a lot of Solar installers just don't understand this.

 

[binky]

sharing an RCD with a solar systems is bad idea, the inverter relays chatter on start-up and frequently trip RCDs out, never mind the above point raised by Dave and Andy. Makes no odds whether solar is in same CU as garage or not as long as CU for garage is on same meter supply. If soalr is generating more than the house is using it will attempt to flow back to grid, if the garage is pulling electric it will flow to garage rather than exit the building. Inverters monitor the grid and output a higher voltage, so like water at a higher level it will flow first, where it goes depends on the electrical loading. If the garage is pulling a load, and house isn't, energy will flow to garage rather than go to grid, so as long as both CUs are supplied by the same meter (not the generation meter) you will still save on your bills.

 

[steptoe]

Just to add to the above, it's because when someone gets a shock and the RCD trips, the Solar PV inverter will continue providing power for up to 5 seconds before it detects loss of grid connection and shuts down. By which time your poor victim is probably dead.

Sadly it seems a lot of Solar installers just don't understand this.

sometimes the RCD wont trip at all,

a lot of the older Hager especially, prob >80% fail on the ones I have tested, [ a few hundred]

the 2nd worst fails are the old MEM stacked boards,

btw, if the PV is switched off these RCDs are tripping normally, PV back on and they fail again,

so there is deffo something wrong,

oh, Ive also had new RCDs with the same problem, from most manufacturers.

 

[Sidewinder]

Steps,

This is because the inverter does not output true sinusoidal a.c.

It is a chopped d.c. wave that sort of approximates to a sinewave, and once it goes into the inductance of the grid that smoothes it out.

It is also a bit spikey, and, has significant dv/dt values which " normal rcd's" cannot cope with.

 

[steptoe]

Steps,

This is because the inverter does not output true sinusoidal a.c.

It is a chopped d.c. wave that sort of approximates to a sinewave, and once it goes into the inductance of the grid that smoothes it out.

It is also a bit spikey, and, has significant dv/dt values which " normal rcd's" cannot cope with.

yer, I remember you explaining a lot of this to me before,

its causing the council no end of issues,

and me hassle sorting it out/bodging it for the council so I can issue a satisfactory on the normal install, then the council bods are 'supposedly' coming round after me and sorting out and certing the PV properly.  if you believe them,  :slap

 

[Sidewinder]

yer, I remember you explaining a lot of this to me before,

its causing the council no end of issues,

and me hassle sorting it out/bodging it for the council so I can issue a satisfactory on the normal install, then the council bods are 'supposedly' coming round after me and sorting out and certing the PV properly.  if you believe them,  :slap

So, what a suprise, the "majority" of "cheap" solar installs are non-compliant perhaps, me sceptical, never, IIRC, I said this months ago, if not years ago.

Another "time bomb" waiting to kill the unsuspecting innocent home owner/DIY'er/Fire Fighter?...

 

[Sharpend]

It'll be alright Sidey, the boys at IET will rewrite the regs to accommodate it!!

 

[Sidewinder]

Sharp,

You REALLY should see the email I sent a couple of hours ago, if it were not that my subs pay their wages, they would kick me out!

Trust me.

I CAN NOT POST IT.

Under any circumstances,

Sorry.

 

[steptoe]

So, what a suprise, the "majority" of "cheap" solar installs are non-compliant perhaps, me sceptical, never, IIRC, I said this months ago, if not years ago.

Another "time bomb" waiting to kill the unsuspecting innocent home owner/DIY'er/Fire Fighter?...

if you remember correctly I mentioned this a couple of years ago,

I have point blank refused to even so much as test to the local isolator on the systems,

limitations are a GOOD thing,

had the head council electrical bod on one job with me and he couldnt believe the state of the installs that got accepted and signed off,

now if I have PV on a dual board [as most of them are] I install a high integrity board [as agreed with them] , and leave the solar disconnected,

I'll put money on all they do is turn up, stick the cables in the RCBO they requested to be left installed, and switch it on.

if the PV is on its own board then I simply ignore it, LIM

the thing is,

what about all these folks doing EICRs on properties that have NO CONCEPTION about solar installs?

are they simply accepting them as satisfactory?

I wouldnt like to be fighting their case when the insurance company says they arent covered,

 

[binky]

 a lot of crap PV installs were done by companies now long gone - should keep me busy for a few years

 

[trevor_clark]

thanks for the reply and sound advice. Have looked at Wylex High Integrity Duel Supply PV CU NH12DSPVH1 MCB which has 2ways unprotected ways and duel RCDs for the other 10ways. I would therefor connect the PV to one of the unprotected way and maybe smoke alarm circuit to the other, both with MCBs. This CU is not cheap £317 + vat + MCBs or RCBO s cost extra. Wonder if there is a heaper way of resolving the problem if not will suffer the  expense have a safe set up. Would finally split main supply meter tails to supply garage CU with 40A main switch to provide isolation of its supply.

Any thoughts or advice would be very much appreciated.

Trevor

 

[Andy™]

splitting tails for PV is probably easiest option. but like i said before, get the marginally trained monkeys who installed it to come an do it correctly instead of sorting it yourself

 

[steptoe]

thanks for the reply and sound advice. Have looked at Wylex High Integrity Duel Supply PV CU NH12DSPVH1 MCB which has 2ways unprotected ways and duel RCDs for the other 10ways. I would therefor connect the PV to one of the unprotected way and maybe smoke alarm circuit to the other, both with MCBs. This CU is not cheap £317 + vat + MCBs or RCBO s cost extra. Wonder if there is a heaper way of resolving the problem if not will suffer the  expense have a safe set up. Would finally split main supply meter tails to supply garage CU with 40A main switch to provide isolation of its supply.

Any thoughts or advice would be very much appreciated.

Trevor

at that sort of money for you to just purchase the CU I'd think it may be a better financial and safer option for you to simply employ a competent electrician that is familiar with solar PV to do this for you,

if you paid my travel, [or laid on some dancing girls and beverages, ] , I could probably do that for not much more than it will cost you simply to buy the stuff,

and, it would be done properly and certificated.

 

[steptoe]

Steps - He's in Essex - I have met some essex girls  :innocent

Its all true  :facepalm:

If he can accommodate you and get the kit and pay for diesel and takes you clubbing - then do it for free - you wont regret it 

the wife,?!?!?!?!?!?!? :slap

I can accomodate myself,

and supply the kit,

he just needs to sort a price that covers my diesel, 

btw, I can do Maldon for £200 expenses, and I can supply a  better spec CU for a much [MUCH] better price,

I think it'd be the beverage money that may be an issue,,,,,,,,,      :slap

If he can accommodate you and get the kit and pay for diesel and takes you clubbing - then do it for free - you wont regret it 

or,

I could do that, 

 

[binky]

meter tail blocks and mini cu is much cheaper option Trev, we test house and change board for the sort of price your Wylex board is costing, and Wylex isn't what it used to be....

Job could be sorted for less than £100 + vat using mini cu

 

[Blue Duck]

meter tail blocks and mini cu is much cheaper option Trev, we test house and change board for the sort of price your Wylex board is costing, and Wylex isn't what it used to be....

Job could be sorted for less than £100 + vat using mini cu and a decent sparky

Medloxks were doing 10way wylex duel arseydee £58+vat not sure if that's an indication of quality?

 

[binky]

we use control gear, can't get much cheaper than that stuff, but have found it to be very reliable other than RCDs tripping a bit to early. Wylex is OK, but have had a few failed MCBs over the years - not fitted one for ages though!

 

[Jono Pashley]

SBS Board? Possibly