b*ll*cks

[Steve Firth]

Received a call from my wife on Friday to say that the RCD had tripped on the consumer unit. Got home to find the immersion heater MCB had tripped. When I investigated the wiring, the wiring inside the immersion heater switch has carbonised and the line conductor was exposed/touching the earth conductor.

This circuit was wired by a "professional" BTW, the only one in the house that remains. I've removed/replaced everything he did over the past few years since every job done by that company was a bodge. The previous owners were the local council and they employed the biggest electrical contractors in the area (still in business) makes me smirk about Part P.

Umm right now, for the purposes of Part P, can I take it that I'm OK to rewire this circuit? It seems by this condition "Replacing the cable for a single circuit only, where damaged, for example, by fire, rodent or impact" as work that does not need to be notified. But this causes concern: "On condition that the replacement cable has the same current carrying capacity,"

Since the original cable seems to be undersized, surely replacing it with something with a greater current carrying capacity is more sensible. Does this need notification? Should I notify the BCO anyway just make his life more of a misery?

Should I just buy some of that red/black cable from eBay?

[Dave Plowman (News)]

Probably connectors not tightened properly. Seems common with pros - I've come across it many times. Watching one at work I wasn't surprised - he was using a piddley little 'electrician's' screwdriver for everything.

Perhaps designed to have 'service' calls just outside the warranty period? ;-)

Who worries about Part Pee? Who's going to know if you replace something?

Immersions are normally run in 2.5mm TW&E, and that's more than adequate. If the connections are properly made. ;-) 1.5mm just about makes the spec if surface run all the way, although it may have problems with meeting earth loop resistance requirements.

What do you think? ;-)

If it worries you and you're intending selling shortly.

[Ian_m]

Not convinced about Prat P either. Just had kitchen done, got Prat P cert, from installer, he even certified my work "yeah looks OK, not using bell wire, must be OK if it works". Had issues with dishwasher, fills, pumps etc but when heating kept starting to pump, then stopped, then started etc. Saw power light flickering on it....hmmmm. Further investigation revealed the dishwasher would work a lot better if he had bothered to tighten the screw on the live conductor on the isolating switch. Also "buzzing" coming from isolating switch for washing machine. Buzzing stopped when I removed the plaster that had been dribbled onto the switch and got inside across the contacts.

[Guy King]

The message from Steve Firth contains these words:

Just replace it with the higher capacity.

No one will know that the /old/ cable was too small. So you'll just have replaced one cable with another of the same size, honest guv.

[Christian McArdle]

They couldn't possibly know what the size of the old cable was. I'd run a single 3kW immersion in 2.5mm cable, unless the run was unfeasably long. Although 1.5mm will normally meet spec, you might as well get as little voltage drop as possible, as it will cost you more in leccy bills than the cost of the cable.

Christian.

[Andy Wade]

That's only in the AD - it doesn't appear in the legislation [1]. Part P itself only requires:

P1 Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.

And the schedule of non-notifiable work contains this item (with no conditions or footnotes, or mention of causes of damage):

(b) replacing a damaged cable for a single circuit only;

ISTM that your proposed work complies with the legislation. Just do the job properly, with correctly sized cable (usually 2.5mm^2 for a 3 kW immersion heater). You aren't increasing the design current of the circuit or the fuse/MCB rating, so an increased conductor size can only result in lower circuit impedances - hence no concerns over disconnection time, etc.

No, use new colours and remember to put the appropriate label on the CU.

[1] SI 2004 No. 3210 The Building (Amendment) (No.3) Regulations 2004, as amended by SI 2006 No. 652 The Building and Approved Inspectors (Amendment) Regulations 2006.

[David Hearn]

I think you might be reading more into that statement that was intended.

Replacing a cable with a larger capacity could be justified. It can carry the same current as the previous cable - therefore it meets the requirement. It also has the added benefit of it being able to carry greater current as well - but I would push that a larger cable meets the "carry the same current" requirement.

I suspect that statement is there to ensure that people don't reduce the size of the cable, not stop them from increasing it.

D

[John Rumm]

I saw one the other day, wired by a "pro" in 6mm^2 cable (the whole run being under 4m from the CU) to a 2.2kW immersion heater...

Think he may have over egged that one a tad!

[Christian McArdle]

Either that, or the customer specified that they might want an all-electric water heating system in the future, which should normally be sized for 6kW to allow two standard 3kW elements.

Christian.

[John Rumm]

Seems unlikely in this case since this was a dedicated mini cylinder (900x300 direct) for a standalone shower in an extension. Having said that, it is possible I suppose, since the "customer" in this case is famous for changing his mind every five mins! ;-)

[Matt]

So wiring it in 700mm2 AAAC with a few layers of black tape won't comply with prat P then?

Maybe it needs to be brown and blue tape?

:)

[ARWadsworth]

I agree with that. It also allows electric shower swaps on a watt for watt basis without notifiction.

Adam

[Steve Firth]

It's a really nasty design for the switch, it has the hold and grub screw for incoming electricity and a screw and washer for the load. Horrid and neither connector seems adequate for 13A. The cable is 1.5mm or rather was it's now replaced.

Yhanks to you and everyone else for the advice.

[Dave Plowman (News)]

Sounds like the 'load' connectors were meant for flex to the immersion.

Does it have a maker's name?

Given the tiny difference in price it's amazing what some do.

[Steve Firth]

Unless my long sight has reached a new all-time low it's an MK but very old looking.

Having seen (a bit of) one of those dodgy builder programs this evening I think that some tradesmen are simply inherently stingy.