Part P certificate: an update and a question

[Bert Coules]

Following the advice in my original thread that I couldn't get a Part P certificate on an installation some years ago without having a completely new inspection, I arranged exactly that with the local BCO's approved electrician.

After a very thorough sessi PARTICULARS OF INSTALLATION AT THE ORIGIN

Means of earthing: Distributor's facility Installaion earth electrode: not ticked

Earth electrode details: all marked N/A

Protective measures for fault protection: ADOS

Earthing conductor: Copper 16mm2 Continuity/connection verified: not ticked

Main protective bonding conductors: Continuity/connection verified - ticked Conductor material - Copper Conductor csa - 10mm2 Water installation pipes - ticked Gas installation pipes - ticked Other - N/A Location (where not obvious) - N/A

I'd be grateful for any comments on this. The BCO inspector was extremely concerned and said he couldn't pass everything unless a proper earth arrangement was installed. But isn't "Means of earthing: Distributor's facility" sufficient?

Apologies for the lengthy post, and many thanks.

[Theo]

Do you know *for what* he couldn't find a main earth connection?

Is this part of the house (an extension) or an outbuilding?

The latter might have a separate earth (which is typically an earth rod) depending on the construction etc (eg a metal framed garage), but the former will typically be connected to the supply earth near the meter/consumer unit.

Is he saying there's no earth continuity between the new installation and the old? That's something you could check with a multimeter and an extension cable plugged into an 'old' socket in the house.

Do you perhaps have some part of it that's missing an earth (eg a socket), and that was the part he happened to pick to test the earth continuity?

(socket testers are cheap:

it could be worth a quick run-around with one to see if it shows any earth faults)

It's not clear whether this is referring to the earthing in the original part or the new extension. If it's the new works I would expect something installed thusly to be sufficient, assuming it's not a separate building.

Maybe you could ask him what he tested and what remedial works he would expect?

Theo

[Bert Coules]

I should have made it clearer: this was a complete rewiring of the entire property. None of the original installation remains.

[Theo]

Ah, OK.

Could you post a (link to) pictures of your incomer/meter/consumer unit arrangement?

As discussed on the other thread, we're looking for your earthing setup. Some examples here that may help:

Theo

[Bert Coules]

something> installed thusly to be sufficient, assuming it's not a separate building. I should have made it clearer that the wiring job was the replacement of the entire installation throughout the property. The inspector electrician regarded the lack of an earth rod/electrode as a serious situation and said that one would have to be added before he could pass the job as satisfactory.

[Bert Coules]

It's not the best quality I'm afraid, given the bright sun and the deep cupboard, but try this:

The consumer unit is located directly behind the meter board and is mounted against the kitchen wall: no wiring is visible.

Thanks for the link. Very useful

Bert

[Theo]

So there appears to be a green/yellow earth wire going into the neutral side of your cutout. Judging by some of the pictures on that wiki page, it could be either TN-S (earth connects to cable sheath) or TN-C-S (earth connects to neutral) but it doesn't look like TT, which would require a local earth rod.

(assuming that wire is connected, and not just hanging loose - if it's loose you'd need to call your DNO to get it rectified)

Without any exposed earthing it is hard to probe for any continuity. The next step in the hunt would be to take the faceplate off the consumer unit to see how things are wired inside. If the main switch in the CU is turned off then most of the CU will be isolated but upstream of the switch will be live, so don't do this unless you're comfortable working around live parts. (eg use a screwdriver with an insulated shaft)

Theo

[Bert Coules]

Thanks for the thought. However, the electrician-inspector did that and reported finding nothing amiss.

Bert

[Bert Coules]

remove > it. Or leave it. Or, as Colin Bignell suggests, I could use the real thing. Does the connection from the earth rod to the house earth have to be made in any specific place?

Bert

[Bert Coules]

earth> from the supply cable, so it was connected to the incoming gas pipe (supply> side of the meter. Thanks for that. I just checked inside the (external) gas meter cabinet. A hefty earth cable is clamped to the incoming gas main and then runs into the house (below floor level, so I've no idea where it goes).

[The Natural Philosopher]

That WAS the real thing.

[Colin Bignell]

Mine goes to the earth terminal in the consumer unit, but it was done well before even the consultation document preceding Part P was issued.

[Theo]

So what exactly did they say the problem was with the earthing?

You have an earth wire that supposedly connects to the incoming supply cable and disappears somewhere we can't see. If it's correctly connected inside the consumer unit, there's no earthing problem. You don't need earth rods unless you're on TT, which you aren't if there's an earth cable to the incomer. (earth rods would not solve a failed inspection on a non-TT system anyway)

If the green/yellow earth wire is in reality not connected to the supply's service head (the black box at the bottom of your picture) or is loose, that's a matter for your distribution network operator (DNO) and they will need to visit since they're the only ones who can open up the service head.

Unless the earth problem was something to do with equipotential bonding (water pipes, gas pipes, metal sinks, etc), which is an entirely different thing (and easily fixed).

Theo

[Theo]

Just to clarify, do you have any electrical installation 'outside'? Swimming pool, hot tub, EV charger, outbuilding (what construction)? They can affect the earthing requirements. I don't think outside wall lights or wall sockets count.

Theo

[Bert Coules]

Two security lights and a double outdoor socket; nothing else. The inspector tested the socket and he also noted that the lights were working, though I don't know if he went any further with them, beyond (as with everything else) checking that they were correctly identified on the consumer unit.

[Bert Coules]

His concern seemed to be entirely centred around the fact that he couldn't locate any evidence that the installation was earthed in a general sense; he talked about the necessity of adding an earth rod.

It was only after he'd left that I looked in detail at the previous chap's certificate and took in the details that I posted earlier. I presume that the inspector saw and understood the "earthed through distributor's facility" item but didn't think it adequate.

He gave me his contact details, so I'll ask him to clarify everything.

Bert

[Theo]

Ask him if he can confirm the earthing system in use (TN-S, TN-C-S or TT), if he measured the earth impedance, and if so what it was (the figure would typically appear on EICR paperwork).

It is possible the installation failed because there was a too-high impedance, rather than no earth at all. The guideline is 0.35 ohms or less for TN-C-S, 0.8 ohms for TN-S, and TT can be hundreds of ohms (depends on local ground conditions for the earth rod).

It could also have failed if the earth conductor was insufficiently sized (<16mm2, although in your pic it doesn't look obviously small) - I think rectifying that would be a DNO matter as the service head is the DNO's business.

If he says it's TT (which would need an earth rod), query what's happening with the earth wire in the meter cupboard and why he says it's not TN-S or TN-C-S.

Theo

[John Rumm]

A long time ago that was common practice for TT systems. Not permitted now. (gas mains have a habit of getting upgraded to plastic!)

That will be a main equipotential bond. It should go back to the main earth terminal in the CU. There should also be one connected to any other incoming service supplied by a metallic pipe.

[John Rumm]

Did you offer him a bowl of water for his guide dog?

(having looked at your photo, there is clearly an earth connection to the cutout. Unless that did not connect to the CU, or was disconnected/high impedance when testing, it seems hard to understand what he was talking about.

Which is what you would expect for a TN-S or TN-C-S supply.

Indeed - not required.

Automatic Disconnection of Supply (i.e. Fuses, MCBs, RCDs etc)

The CSA of the wire is appropriate. The "verified" is a bit ambiguous - does that mean it was tested and failed, or it was simply not tested? (the latter seems unlikely)

All as expected. Two incoming services, and no other incoming connections that could import an earth connection into the equipotential zone, and not extraneous metalwork...

(does the place have CH with metal pipes? One might expect the pipework to be treated as an extraneous conductive part since the CH pipework can provide a conduction path all around the house)

If it was tested and working then, yes. I find it had to see how a complete inspection could be done without checking things like external earth loop impedance, and testing maximum prospective fault current, or testing the fault impedance on final circuits.

[Bert Coules]

other incoming service supplied by a metallic pipe. Thanks for that. The only other service (unless phone and aerial cabling counts) is water; by the time it enters the house the main is plastic but I don't know if that's true for the entire length of the pipework from beyond the boundary. Internally, it's a mixture of plastic and copper.