AC Isolator

[dougalthedog]

Hi,

Is there an accepted definition of "accessible" e.g. from G83 as the DTI guide requires the AC isolator to be in an accessible location. For example is a loft considered accessible?

The DTI guide shows 2 isolators where the inverter and meter are physically separate, however BS7671 (which is more recent) clearly shows the AC isolator located adjacent to the inverter and only an overcurrent device at the CU.

Also in another thread I note a poster states it is not acceptable to connect a PV system to a 16A MCB on the RCD side of a (presumably single RCD) split load box. Is this correct and if so why - or was the poster referring to TL inverters only?

Is it to minimise interruption of other services in the case of earth leakage? Clearly unless the cable is buried >50mm etc RCD protection is required by BS7671.

What is normal practice - fit 2 isolators when the inverter is remote?

Thanks.

 

[newfutile]

we fit an ac isolator at each end of the 4mm t&e

 

[northernsun]

There doesnt need to be 2 isolators at both ends, this is only when there is some speration between the two- which is quite a lot. The lockable isolator is the one that goes at the mains position, The one at the inverter location is for local switching and can be just a normal double pole isolator- although our MCS inspector argued the ---- on this when I mentioned it. Regardless I always install 2 rotary isolators anyway, its not that much more work or money.
I have noticed a few companies doing the other way round, ie the locakable at the inverter and a switch at the con-unit, though for aesthetic reasons and I would be interested to hear peoples views on this. The requirements for the mains located isolator are that it should be double pole and lockable in the off position- with no specialist equipment.
In lots of new builds this can be an issue as people don't want a horrible rotary isolator on display in the hallway. I have seen a few installs where the isolator at the mains is just a double pole switch or even in one case a fan isolator switch because it has a key lock thingy (!!)- because it looks nicer. In these cases I would like some sort of double pole MCB in the board, but this could only be locked off with a sparkies clamp- but I dont think this qualifies.
With the ofgem compliant din mounted meters it would be good to have everything contained at the con unit when the con uint is on display.
I was looking in to this issue a bit back and then forgot about it (like you do) and did'nt dig any more, It would be gret if they are now saying that you just have an MCB at the board!

 

[Worcester]

We nearly always install a new CU just for the Inverter circuit and so a re looking at the guidelines closely, - we've seperately had a NAPIT and an NIC inspector (not MCS..) agree that in principal a double pole main swith in the CU if fitted with the ability to be locked only in the off position id adequate.

So long as it's properly labelled, I don't see why it shouldn't be adequate either - others thoughts?

We ALWAYS put an isolator near the Inverter, and only don't put a second one in if it is clearly visible from the CU (line of sight and obviuos!)

 

[northernsun]

Cheers Worcester. Thats pretty much what I was thinking, but i had heard some conflicting things. The main one being that the lock needs to be locked off without any extra gear- such as an mcb clamp. I dont see the problem if one os these is left at the CU and, as you say everything is properly labelled. The jobs I was interested in this for were all housing associaition new builds and the client really did'nt want the isolators on display. I erred on the side of caution, despite wanting to do things as above, I didnt want to be bit on the behind for such a big job. Like I said though, I have seen some ridiculous solutions such as a fan isolator as a lockable switch.
I've not done a install privately where this has been an issue- with the CU open on a bare wall, but I think I will be doing as you do. Most of the time a rotary iso with the gen meter mounted on top will do.

 

[Worcester]

Here's a classic example, Our 50mm trunking, on the right, from the right, Gen Meter, AC Iso, Our CU, (MCB and Main switch) CU straight to 4 way henly block for incoming, house CU, Night Staorgae Heater CU's and our CU, sorry for quality of photo, only had phone with me.

Classic case where if we'd installed a 'permanent' MCB locking device we wouldn't have needed to install the AC Isolator.


I do like the big yellow cover though, it does kinda tell you what it's about.! (anyone make yellow CU covers?)

 

[MorganPVI]

You could install the inverter there and it wouldn't look any less crowded!!

Our customers get 2 AC isolaters unless the inverter is next to the CU.

 

[northernsun]

Classic case where if we'd installed a 'permanent' MCB locking device we wouldn't have needed to install the AC Isolator.

Yup!

If I was to do away with the iso I would also be looking at the din rail mounted gen meter to go with it and have everything self contained in one little box. Not done it yet, not even used the mounted meter but I've got to say it would look good on someones wall.
Anyone used one yet? I saw some that midsummer energy were stocking a few months back.

 

[BruceB]

I have used a few of the din rail meters now. Useful where space around CU or inverter is limited or very visible and you or the customer do not want an extra box. Disadvantage is they cost a few pounds more in the quantities I buy them and for older eyes can be a pig to read. The standard Rayleigh PRO1D is an unilluminated LCD display and if you get a shadow falling on it in a poorly lit utility room then you need a torch to read it.
Regards
Bruce

 

[Worcester]

Check this out - a really neat solution from Sibert - Give Andy O'Leary a call on 0777 5427243

The examples shown include variants regarding the generation meters included in the enclosure. These are, in particular, the L&G 5235 range and the Inepro PRO-1D (DIN-rail mounted) meters. Other meters such as the larger Inepro PRO-75D could also be used if a larger display is required.

Single or double-pole MCBs as well as optional RCDs (AC, A or B type) can also be integrated into the solution as well as AC surge and lightning protection devices (from Dehn) if required. Costs will vary according to the particular configuration required.

 

[dougalthedog]

What I was wondering is would it be acceptable to fit the lockable isolator in the loft, next to the inverter and only have the MCB, or indeed seperate CU at the metering point. It would seem to depend on whether a loft is considered to be accessible or not.

Any thoughts on why / whether connecting into the RCD side of a split load box would be unacceptable?

 

[Worcester]

Nope, just read the DTi guide

Can't see how that would be acceptable, it's not just isolating the inverter for maintenance purposes on the PV system (that one according to the DTi guide doesn't need to be lockable ) , it is to isolate the generator ciruit from the consumer circuits / DNO supply.

 

[Worcester]

You could install the inverter there and it wouldn't look any less crowded!!

Problem is that is actually the front bedroom! (Dormer / Chalet Style house)

Inverter went outside on the wall

 

[BruceB]

It is not always unacceptable to connect into the rcd side of a split load box. However:
- it is unacceptable if the manufacturers instructions say minimum of 100mA rcd (eg SMA TLs) , because a split load box rcd will be 30mA;
- it is unacceptable with TT because the rcd forms part of the ADS protection and the regs require the pv circuit to have its own protection;
- it might be unwise in a normal situation if the inverter design results in leakage currents which combined with others in the house might lead to unwanted tripping of the rcd.

Regards
Bruce

 

[SibertSolar]

Check this out - a really neat solution from Sibert - Give Andy O'Leary a call on 0777 5427243

View attachment 7597View attachment 7598

Many thanks Worcester,

At the moment we are still getting a feel for demand and suitable pricing levels but the main aim really is to demonstrate that we can provide the pre-assemblied solution according to your requirements.

For those that have a situation where they would prefer to fit a DIN-rail gen. meter (such as the PRO1D) within a unit also containing MCBs/RCDs etc without the need for an AC isolator, we can provide 4, 6 or 8-way Garage CUs with double-pole MCBs (and RCD if required) and DIN-rail meter (PRO1D is 1 module width, PRO75D is about 4 I think) to suit your requirements. Our MCBs and RCDs can be provided with their own lock-off devices too.

Andy