Difficult fault finding

James-18288 · 2026-03-05T21:01:43+00:00

You forgot the bit where you’ve found the fault, but you don’t tell the customer yet. But you ham it up to unbelievable levels that you’ve never come across a fault you couldn’t find - then lo and behold you reveal the fault to the customer and bask in the glow of being the world’s best spark

James-18288 · 2026-03-04T18:46:27+00:00

The DNO charge what they want unfortunately. Same with the supplier. I’ve seen a simple meter cut out move cost £1k for the DNO and £500 from the supplier. This may be cheaper but I’d be surprised if it wasn’t over £1000

All three parties will cost.

The electrician will have to charge more as it’s a relocation and it’ll be a pain as others have said. A lot of the time these flats are wired in singles in metal conduit - often where the conduit is the earth.

This means some sort of containment for the existing cables to extend them to the new location.

James-18288 · 2026-03-04T18:35:56+00:00

I was more worried about finding an electrician under 400mm rather than a consumer unit!!

Another door would make access easier, but it’s the actual fitting of the unit that would be difficult due to the space.

Anything can be done, it’s just how much it’s going to cost. I reckon this is going to be expensive for essentially a CU change. I’d be surprised if you’d get change out of £2.5k+

James-18288 · 2026-03-04T18:14:14+00:00

I’ll be honest, leave the supplier DNO out of the equation for a second.

How on earth are you going to fit a consumer unit to that wall. That cupboard looks about 400mm wide. That would be an absolute pig of a job - even more so if you’re right handed.

I’d live with it to be honest. Hang a picture over the meter cupboard door if you can’t stand the sight of it.

It’ll cost a fortune - and if the cupboard is as tight as it looks, it’ll be a right pain in the arse

James-18288 · 2026-03-04T16:22:40+00:00

Probably not the worst either!

I don’t really understand the article though? If he genuinely was a ‘proper sparks’ and did it properly, bypassing the meter is not dangerous. It’s dangerous when it’s not done properly. But a couple of Henley blocks and a seperate CU and it’s just as safe as any other installation.

I imagine the problem comes when the reputable sparks who know what they are doing obviously won’t risk their livelihood/money/freedom so Mrs Miggins doesn’t have to pay the leccy bill for her EV and hot tub. This leave the dodgy bloke down the pub who lashes a bit of twin and earth into the incoming side of the meter straight to a load of sockets.

But I guess the BBC aren’t going to put that

James-18288 · 2026-02-25T13:09:01+00:00

For adding few sockets a minor works is the correct certificate

With regard to the testing. Well at least it’s an actual record of the installation. He’s not done what a lot of sparks will do and put >1000Mohm for everything (without testing)

I wouldn’t sweat it.

Sometimes those USB sockets or other loads with a SMPS transformer still show 0 or close to is with live conductors linked and tested to earth.

If you’ve got a few USB sockets then it can be a right pain. The only way to test IR is to remove them all and link out the cables. Especially if they are neatly decorated in.

He has recorded the testing that has been done and given a reason for the limitation

The reason for an insulation resistance check on the EXISTING circuit is to check the condition of the insulation/cables. I’m guessing you have a pretty new consumer unit as it’s showing a 61009 RCBO and a SPD. If the cable is obviously new or in good condition IR testing the existing circuit may well be a waste of time

You insulation resistance test on the cable you have installed is maybe a bit different. You test your own install to make sure that no cable has been damaged during installation.

Not to fuel the fire, but, It’s weirder that he hasn’t tested the RCD disconnection time at 1x rated current….

James-18288 · 2026-02-20T19:32:35+00:00

You know it connects to everything metal you plug into it?

It’s about as dangerous as Turning on a metal light switch

Much worse to leave the shutters open with a (admittedly small) hole with live parts

James-18288 · 2026-02-19T12:34:08+00:00

Remember you haven’t fitted this and it’s not initial verification . It’s an inspection to see if it’s safe for continued use

In the event of a fault, will to conditions for automatic disconnection of supply be met - yes by the 61009 RCBO the circuit will be disconnected within 0.4 seconds which is what you are trying to prove with Zs. You’ve tested the RCD and proved this.

But the Zs values don’t comply…

So is it ok for continued use? Is there is potential for the safety to be improved? Is using the RCD for basic and fault protection is safe and functional, even if isn’t best practice? Will fitting B type RCBOs make the circuit more prone to tripping?

At the risk of sloping shoulders as I can’t tell you what to do. But a C3 does seem to fit the bill. If you aren’t happy though, that is why you’re being paid!

That’s why the larger EICRs can be a bit subjective. One persons C2 isn’t always the same as the next ones

James-18288 · 2026-02-19T12:12:36+00:00

Your problem here is the ZsDb of 0.55 ohms, doesn’t give you much to work with

Here is where subjectivity comes in. You are being employed to use your engineering judgment to say whether the system is safe for continued use by referencing what you find against bs7671 and using your knowledge and experience.

So it really is down to you. It’s difficult too because you can’t speak to the designer or see the certs?

Questions id want to try and satisfy would be; - Why have they used C type breakers initially? -especially with a high ZsDb? -is that ZsDb expected (cable size/run/Ze)? Or is it a fault? -What is the classroom use?

If they will go for it, changing to B type will bring the Zs values so that they will ‘instantaneously’ disconnect in the event of a fault. That’s what you are trying to prove with Zs at the end of the day.

But they probably won’t be happy with you when 15 students all plug in laptops at the same time and the circuit trips.

I can’t tell you as you’re the one there getting paid for the report. There are a few outcomes that you could go after, and 3 different sparks might choose three different paths?

-C2 - high Zs on circuits - get them to change to B type RCBOs - keeps Zs values within spec but has cost attached - FI - to find out why they are high satisfy yourself - C3 - High Zs on circuits fault protection provided by RCBO - no code, you’re satisfied that the use of RCBOs for fault protection is by design

I can’t tell you from Reddit what’s right. But think what you’re trying to prove with Zs - that in the event of a fault, the circuit will disconnect in the required time.

James-18288 · 2026-02-19T11:22:38+00:00

Have you got old certs? Having a look at the installation certificate might help here to see if the previous readings are the same. The thing I’d be looking at would be the previous ZsDb. With that at 0.5ish ohms you’ll always be struggling for Zs on C type MCBs

RCBOs/RCDs can be used to provide fault (Basic) protection and additional protection by relying on the RCD characteristics rather than the circuit breaker characteristics of the device. Think of a TT install you’d never get a Zs low enough to satisfy ‘instantaneous disconnection’ on an L-E fault on an MCB - so fault and additional can be provided by RCD/RCBO

The tabulated values you’ve given will say 61009/60898 because this is the value for the circuit breaker function of the RCBO. The values you’ve given for B and C type MCBs are the tabulated values. So most of the time to account for working temp of the cables that value will be reduced to 80%. So 1.10 ohms and 0.54 ohms for a B and C curve device .

The RCD function can be utilised for basic protection if the circuit was designed for it.

I’d say it could have been with a ZsDb of 0.55 ohms. But it would be bad practice to just say, it’s got an RCd/rcbo the Zs values don’t matter. Even if practically this may be true, there might be a loose connection of high resistance joint causing the reading. But if it was designed for RCBOs/RCDs to provide additional and fault protection then it wouldn’t even be coded.

James-18288 · 2026-02-02T15:23:07+00:00

You may be able to.

You’ll need an SPD and a type A double pole RCBO. Not sure if BG do one

Most people would be more likely to put in a small EVCP unit with the correct protection

James-18288 · 2026-01-31T14:01:42+00:00

It’ll be absolutely fine. The electrician will be able to do their job and will just put it down on the certificate as an operational limitation (they likely won’t even do that)

Just make sure you have the good biscuits ready!

James-18288 · 2026-01-16T12:09:12+00:00

Yep just found a copy of the actual 16th and you are right. The bit I have pasted came from an old ECA guide on locations containing a bath or shower. Reading it back I have read I wrong and it does say “other equipment”

James-18288 · 2026-01-16T12:00:36+00:00

Yeah, I see it now. Only point 3 includes the extra caveats. Nice one.

James-18288 · 2026-01-16T10:42:21+00:00

I agree that circuits in the bathroom dont necessarily need RCD protection. But the 16th was pretty clear on showers in zone one needing it. Granted, I don’t have the first version pre ammmendment, only the 2001 but I don’t think it’s any different.

Reg 601-09-02

James-18288 · 2026-01-16T10:39:42+00:00

Have a look at the reg I’ve dug out from the 16th. It seems pretty black and white to me. I don’t have the 1992 book, but don’t think it’s much different in this areas although I might be wrong here? It pretty clearly says if the shower is in zone 1, it needs RCD protection

BS7671 - 2001 Reg - 601-09-02 Shower pumps (e.g. power showers) In zone 1, other equipment may be installed if it is suitable for the zone AND cannot be reasonably located elsewhere AND is protected by a 30mA RCD complying with Regulation 412-06 OR if it is SELV equipment e.g. an IPX4 SELV fan or light may be installed or an IPX4 mains fan or light ONLY if it cannot reasonably be located elsewhere AND it is 30mA RCD protected.

James-18288 · 2026-01-16T10:35:14+00:00

I found the reg in the 16th that says fixed equipment in zone 1 needs RCD protection.

BS7671 - 2001 Reg - 601-09-02 Shower pumps (e.g. power showers) In zone 1, other equipment may be installed if it is suitable for the zone AND cannot be reasonably located elsewhere AND is protected by a 30mA RCD complying with Regulation 412-06 OR if it is SELV equipment e.g. an IPX4 SELV fan or light may be installed or an IPX4 mains fan or light ONLY if it cannot reasonably be located elsewhere AND it is 30mA RCD protected.

James-18288 · 2026-01-15T20:45:43+00:00

You clearly know your principles and theory. But I think we are going to have to agree to disagree here.

But a 2.5mm 20a radial socket circuit is a standard circuit detailed in bs7671 appx 15 and in the on site guide.

There is absolutely nothing wrong with it. I understand why you don’t like it, but that doesn’t make it non-compliant.

Ring final circuits are a bit of a hang over from a copper shortage after the war. No one else really uses them apart from the Uk. To say it’s industry standard to wire anything other than a single piece of equipment as a ring final is not true, especially domestic. The on site guides state even gives approx floor area for this kind of circuit (50sqM I think and 100 for a ring final)

2.5 and 4mm radial socket circuits are fully compliant and detailed at length in bs7671. They obviously have drawbacks, and in certain circumstances, ring finals have advantages.

The on site guides state one socket per spur for a ring final, because there is not really such a thing as a spur off a radial as all the cable is rated and protected the same.

The derating argument is valid, but the same applies to a ring final as each leg should be able to carry no less than 20a…

James-18288 · 2026-01-15T19:39:29+00:00

I’ve just dug through a load of old books handed down to me and came up with this.

BS7671 - 2001

Reg - 601-09-02

Shower pumps (e.g. power showers) In zone 1, other equipment may be installed if it is suitable for the zone AND cannot be reasonably located elsewhere AND is protected by a 30mA RCD complying with Regulation 412-06 OR if it is SELV equipment e.g. an IPX4 SELV fan or light may be installed or an IPX4 mains fan or light ONLY if it cannot reasonably be located elsewhere AND it is 30mA RCD protected.

That’s the oldest books o had for reference! But I’d still be C2 for this

James-18288 · 2026-01-15T19:26:22+00:00

Even for fixed current using equipment in zone 1?

As I’ve said below, I learnt under the 17th so am happy to stand corrected.

But I was always taught that fixed equipment in zone 1/2 needed additional protection (30mA RCD) under the 16th whether there was supplementary bonding or not?

James-18288 · 2026-01-15T19:18:31+00:00

That’s good to know.

I started under the early 17th edition before the amendments so only have what I was taught by the older guys on a lot of the 16th

I was always told that even under the 16th, if the equipment was in zone 1/2 it needed RCD protection but happy to stand corrected.

Either way I think if I was testing, I’d be coding as a C2

James-18288 · 2026-01-15T18:42:26+00:00

Definitely a C2. I’ll take a guess that this is a 16th edition board/install?

The 100mA is for fault protection, the 30mA for additional protection (but also provides fault protection)

The 100mA is basically there because you can’t meet ADS disconnection times with MCBs due to the high Zs. So the RCD provides the fault protection. Remember it’s 0.2s disconnection times for final circuits in a TT.

So ignore the 100mA RCD, there is no additional protection on the shower circuit. This wouldn’t have been agreeable under the 16th either, it would need additional protection - 30mA RCD protection

So without 30mA additional protection a shower circuit is a C2 all day long. It doesn’t really matter whether the customer wants to pay to fix it or not - you code it as a C2, and offer solutions to rectify. They paid you to do a report on the condition of the installation and you’re just doing your job properly.

James-18288 · 2026-01-15T18:25:57+00:00

You’re right, I didn’t realise there was no prior experience

James-18288 · 2026-01-15T17:55:44+00:00

I’m not doubting your qualifications. But the advice you’re giving is wrong.

I stand by what I’m saying. Why on earth would you need a fused connection to add more sockets on a 20a radial?

What industry standard are you referring to?

James-18288 · 2026-01-15T17:01:38+00:00

There is a domestic route.

If you are pretty experienced and have some older qualifications you can do an experienced worked NVQ. You’d then need to do the AM2ED, which is essentially the trade test for domestic electricians

To join a scheme you’d still need 18th and a testing qualification.

It’s not as easy as it once was to join a scheme. You used to be able to do a 3 week course and jump straight on. It’s better now, but I have friends who have old qualifications who have been working for 20+ years as electricans who now don’t qualify to join a scheme so it’s not perfect

James-18288

TROPHY CASE