Is this meter redundant?

Don't know about redundant but it appears to be privately owned sub meter that's fed from the C.U, unless the PVC is just passing through the trunking, so not an Energy Supplier's meter.

Whether it's in use and needed is another thing.

Is it a PV generation meter, missing a few stickers?

SparkySy said:

Is it a PV generation meter, missing a few stickers?

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Give that man a beer! OR several!

I've just found the house on RightMove. I hope that I'd have noticed the panels (!), and obviously with the trunking cover off I'd have at least seen it was in use, but not necessarily the direction of travel.

But it does highlight why the regs require "two sources of supply" stickers.




If it does turn out to be TT and the main switch RCD is the only fault protection then I'm not happy about the solar back-feeding this and increasing the disconnection time to however long the inverter takes to notice the lack of mains and turn off, which is typically 500ms.

timhoward said:

If it does turn out to be TT and the main switch RCD is the only fault protection then I'm not happy about the solar back-feeding this and increasing the disconnection time to however long the inverter takes to notice the lack of mains and turn off, which is typically 500ms.

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Yes, you should never have a generation source like PV attached to the load-side of any "additional protection" RCD.

Find if its a 100mA delay incomer and circuits have their own 30mA RCD/RCBOs but otherwise it is not a good situation.

Anyone know the relevant reg off hand?

pc1966 said:

Yes, you should never have a generation source like PV attached to the load-side of any "additional protection" RCD.

Find if its a 100mA delay incomer and circuits have their own 30mA RCD/RCBOs but otherwise it is not a good situation.

Anyone know the relevant reg off hand?

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30ma main switch. Just got photo.

551.7.2 - I've just been reading.

I've got various concerns.
No labelling.
No isolator there. The CU isn't labelled either, I suspect the cooker circuit has been re-purposed.
I need to check earthing - if it's PME then I think that 551.7.2 (iii) is an issue.
And point (iv) concerns the bit I was concerned about regarding disconnection.

Also I believe line and neutral conductors are supposed to be isolated which the MCB won't do.

I'm far from a PV expert, but this feels wrong on a number of levels.

should definitely have a double pole isolator and appropriate labels.
Or is it the 16a MCB with no description, doesn't look like a huge PV system. It may or may not need RCD protection depending on the cable run and the MI. And would preferably be type A at least.
You need to confirm if it is TT or not as that will determine the next part of the upgrade!

It should have two isolators one for the d.c. side and one for the ac/inverter output side.

pc1966 said:

Yes, you should never have a generation source like PV attached to the load-side of any "additional protection" RCD.

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Unfortunately finding that is commonplace from the early PV installs, but I'd argue this one is worse as it potentially could be stuffing up fault protection too.

SparkySy said:

Or is it the 16a MCB with no description,

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I've been sent a photo with the cover off now. The joys.

SparkySy said:

You need to confirm if it is TT or not as that will determine the next part of the upgrade!

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Agreed - before you realised it was PV I was thinking of moving the MET, moving that meter and getting an 11 way Fusebox in by moving it down a little. At that point it was academic whether it was TT or not, with tails clamp and double pole RCBO's anyway.

If it's TT things certainly get interesting in terms of design and space!

timhoward said:

If it's TT things certainly get interesting in terms of design and space!

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If the PV is fine on a type A 30mA RCD then an all RCBO board that is neutral switching, like the compact Fusebox or Wylex RCBO, is fine. Subject obviously to the PV feed being off its own RCBO.

A friend of mine had a PV system with an ABB inverter and it kept tripping the installed 30mA RCD. On actually reading the instructions I found it was fine for 300mA type AC according to ABB, so changed the original installers' RCD for a 100mA selective one and no further trips. In that case it was SWA out to the inverter so additional protection not needed.

Here it looks like T&E inside the home so probably you would have to have 30mA anyway.

I agree with @pc1966 above comments it does look like twin and earth for the PV, and Fusebox is the way with the mini DP RCBO's, where you could wedge an AC isolator is another question and as mentioned above should have DC isolators for the PV strings although I find these are usually positioned close to the inverter.
On another note, the picture of the front of the house, is that the supply cable clipped across the front of the property? If so it may well be TT!
We have a row of cottages local to me with a very similarly lashed in supply cable.

Thanks @pc1966 and @SparkySy .

Yes, it's an overhead supply lashed to that wall. The earth electrode reportedly has nothing connected to it but there is a loose wire nearby....
That and the 30ma main switch leads me towards expecting it to be TT by design, there is however a slight busyness of earth wires to the left of the cut-out that needs a look at, as well as testing it etc.

They don't yet live at the house, they have turned everything off, and I'm meeting them there on Tuesday.

Right - back to the snooker....!

I've been and had a look now.
The easy bits - supply is TNCS.
PV circuit is T+E clipped direct and then run in PVC conduit outside to the inverter (above ground at all times).
The inverter is outside and has AC and DC isolators local to it.

One obvious issue is the lack of 2 sources of supply labels inside and outside.
I believe it's fine to use a (decently labelled) switched N RCBO as the inside PV isolator.




I'd appreciate a bit of guidance from the solar bods - I think the 2nd part of 551.7.2 comes into play as the 'genset' is on the load site of a protective device for a final circuit. (or is this now not classed as a final circuit?)

My big question is ident 551.7.2 iii - "The line and neutral conductors of the final circuit and of the generating set shall not be connected to Earth".
Am I reading it right that this means the inverter earthing shouldn't be via the final circuit and the TNCS link?

The CPC's are connected inside the AC isolator at the moment.

There is a disconnected earth rod there, ra of 40 ohms but this goes to the MET inside and more likely pre-dates the TNCS supply.



Practicalities aside, would it be better to dream up a way to run the PV from it's own board connected to the origin?
Many thanks.

timhoward said:

I'd appreciate a bit of guidance from the solar bods - I think the 2nd part of 551.7.2 comes into play as the 'genset' is on the load site of a protective device for a final circuit. (or is this now not classed as a final circuit?)

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It is on the load-side of the RCD for additional protection and that is not acceptable. Is it on a separate MCB?

timhoward said:

My big question is ident 551.7.2 iii - "The line and neutral conductors of the final circuit and of the generating set shall not be connected to Earth".
Am I reading it right that this means the inverter earthing shouldn't be via the final circuit and the TNCS link?

Click to expand...

I think this is prohibiting your own TN-C arrangement. If the PV system is capable of running in island mode than it would need to isolate the supply and re-establish "neutral" by earthing the now-floating N line conductor, so at any one time there is only one N-E link.

I think most PV do not, they shut down on loss of AC supply.

The inverter CPC should be on the same earth as the installation.

timhoward said:

There is a disconnected earth rod there, ra of 40 ohms but this goes to the MET inside and more likely pre-dates the TNCS supply.

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No harm in reconnecting it if generally OK condition.

timhoward said:

Practicalities aside, would it be better to dream up a way to run the PV from it's own board connected to the origin?
Many thanks.

Click to expand...

If you can run it in SWA than you don't need it RCD'd, but with an RCD incomer that is not changing much.

Check the inverter data sheet - if they say it is OK on 30mA protection then you can do it as it is. I'm still a little uneasy as nailing the cable is not giving you the same protection due to the inverter shut-down delay but if it is not hidden just below the surface not a likely issue.

pc1966 said:

It is on the load-side of the RCD for additional protection and that is not acceptable. Is it on a separate MCB?

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Yes, at the moment it's on it's own MCB with a 30ma incomer.

pc1966 said:

I think this is prohibiting your own TN-C arrangement.

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Makes sense now, thanks.

pc1966 said:

I think most PV do not, they shut down on loss of AC supply.
The inverter CPC should be on the same earth as the installation.

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Again thanks. The manual is clear that it is transformer-less hence definitely no island mode.
I'm glad I was over-thinking that one.

pc1966 said:

If you can run it in SWA than you don't need it RCD'd, but with an RCD incomer that is not changing much.

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The proposed new CU would be ordinary main-switch and SP+N RCBOs, including one for this circuit.
To me this seems to be an improvement as if the PV RCBO operates it disconnects line and neutral immediately from the rest of the installation. (At the moment the whole board stays live until the inverter shuts down which is my main beef with it)
I accept that the additional protection element of the RCBO won't operate correctly if the inverter is powered up. On the other hand additional protection is barely justified anyway (see below).

The manual says that where the local wiring regulations require RCD protection of the supply circuit this can be provided.

The T+E and PVC conduit is entirely visible, never buried, with exception of where it passes straight through the outside wall. I think pragmatically speaking that isn't enough reason to justify changing the wiring to SWA.
I'm also a little bit loathe to modify it as I haven't paid the extra pound of flesh to be micro-generation scheme certified and (ideally) wouldn't want to risk compromising the customers ability to claim the FIT by changing it in any way.

So at the moment my intention is new CU, SP+N RCBO for PV providing means of isolation at origin, lots of signage, and the rotary isolators outside are fine. If anyone feels I'm getting this very wrong then do speak up!