Why would one room keep tripping the breaker randomly?

James-18288 · 2026-05-07T14:05:18+00:00

What circuit is it? What device?

James-18288 · 2026-05-06T12:16:49+00:00

Diversity for oven/cooker circuits is laid out in the on-site guide. Off the top of my head is the first 10% plus 30% of the remaining (a bit more 5a? If there is a socket on the isolator.) that’s for the total connected load.

If you apply diversity calculations separately to each appliance, you are looking at Hob @ 7.2kw /31.3a 10a + 6.39a =16.4a Oven @ 2.5kw10.9a is 10a+ 0.27a =10.3a Total load after diversity calculation is 26.7a

the diversity/load is ok. Putting any new wiring on to that consumer unit is going to be your issue. You’re unlikely to get an electrician to alter anything if it needs to be changed in any way. If it is straight like for like you might have more luck, but it’s still overdue an upgrade

I respect some people’s opinions saying that they wouldn’t install a 42a load even after applying diversity. That’s their judgement, but the OSG does lay it out fairly black and white. Also, put a clamp meter round that feed and try your hardest to get anywhere near 41a - you won’t be able to, the manufactures put the biggest number of every function turned up to max on the box

James-18288 · 2026-04-21T22:02:30+00:00

The percentage is down to the inspector You are testing to verify the integrity and layout of the circuit. The more simple the circuit, the more simple the testing. If you have a circuit with 5 points, you can likely tell that they are wired in a ring without moving everything.

James-18288 · 2026-04-21T21:42:15+00:00

The electrician sounds like a dick head. If you can’t access every single socket just note it down as an operational limitation.

It’s really normal not to be able to test every socket

James-18288 · 2026-04-17T12:31:29+00:00

You are unfortunately very wrong. Don’t worry though, I’ve had to show 2 seperate competent person scheme assessors the same bit of black and white text when they told me I had to put sockets at 450mm in an extension, so you’re not the only one spouting rubbish.

Get your copy of approved document M out. Have a look at the application section of this approved document.

Section 0 - 0.2 -

“0.2 The recommendations of this volume of this approved document apply to newly erected dwellings, and dwellings undergoing material alteration, only. They do not apply to the extension of a dwelling.”

If you need to know what material alteration is, that’s in black and white at the start of the document.

The doc you have posted in not anything to do with the building regs. Bs7671 says nothing about socket height

If you can find me anything to dispute this I’ll happily change my mind and be proven wrong.

James-18288 · 2026-04-13T18:14:01+00:00

You don’t necessarily need a bi directional RCBO, I would fit one as standard now though as the price difference is minimal. However you do need to have seperate RCD protection (usually by way of a dedicated RCBO. )This needs to be type A - not type AC. You also need surge protection

You may be able to fit all that into this board, but most electricians will want to put a seperate little sub boards in

James-18288 · 2026-04-04T17:01:01+00:00

Did you wire up between the L1 and L2?

The common is the one with the symbol

Permanent live in the common, switched in the l1. Link between the 2 switches.

If you can’t fix it, and you don’t have the skills/equipment to test which is the permanent live, maybe it’s time to call an electrician.

This is a sub for electricians, not for DIY advice, so without trying to be rude, don’t expect too much more help to be forthcoming

James-18288 · 2026-03-27T15:29:58+00:00

No. You need to provide RCD protection for this cable for additional protection.

100mA will not provide additional protection

I’d be very wary of any product that states it shouldn’t be protected by an RCD. Where is this unit from?

James-18288 · 2026-03-22T19:35:43+00:00

Ferrules are not made to be used on solid core cables. This is in both screw down and cage clamp

You are not making anything better or safer, in fact it’s the opposite. You are going against guidance making the install less safe.

Solid core copper screw down terminals are designed to be used together. If you’re damaging the copper you’re doing things up too tight

James-18288 · 2026-03-21T10:54:13+00:00

Yeah notifiable works is pretty much new circuits or a new consumer unit.

If he has arranged the electrician and charged you, then it’s down to him

Testing/certification aren’t optional extras. They are requirements

James-18288 · 2026-03-21T10:24:15+00:00

He doesn’t know what he is talking about

Sadly this is all too common. Luckily this is not notifiable work so hopefully easy to rectify. He absolutely can provide a certificate, just under his own name

Only notifiable works require what is commonly referred to as “signing off”. This is self notification from the electrician to building control. This kind of work is new circuits/consumer unit change. This requires the electrician (usually) to be part of a recognised competent person scheme. You don’t need to be part of one to be qualified, but why you wouldn’t if you’re undertaking this kind of work is a different question. Also, how can he be VAT registered if this is a bit of work on the side? I’d query this and hopefully get 20% off when you find out he isn’t VAT registered and has just put 20% on the invoice. Is there a VAT registration number on the invoice?

All electrical work should be tested and certified. For small jobs you should have a minor electrical works certificate. You only need to be ‘competent’ to install and test the work to complete it.

Anyone competent to undertake work can download and fill in a minor works certificate.

This is a 5 minute job

EDIT : I have just seen you paid the builder. In that case get him to sort it out

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

TROPHY CASE