Green Building Forum - Electric cables

Electric cables

ringi — Wed, 17 Feb 2016 13:24:23 +0000

Posted By: Paul in MontrealRCD breakers are still supposed to act as overcurrent breakers, just like regular ones - though maybe in the UK the RCD is a separate thing and isn't bundled into a "MCB"?

In the UK, a RCD will be integrated into the main switch of a consumer unit, so there is only 1 or 2 RCD covering all wiring in the home. Great if you trying to track down a fault Hence I like RCBO.

Electric cables

Gotanewlife — Wed, 17 Feb 2016 15:08:16 +0000

But RCBOs are expensive otherwise I would have every circuit on one!

Electric cables

cjard — Wed, 17 Feb 2016 17:28:51 +0000

They aren't that expensive. My CU has 20 ways, all RCBO and it was about 200 quid I think. Sure, a fully populated dual RCD plus 18 MCBs would have been half that, but it's a drop in the ocean of the rest of the build.. What's 100 quid in the face of a Â£20,000 bill for the windows?

Consider that a whole house RCD tripping ruining the contents of the freezer while you're on holiday would probably cost you Â£100 in food..

Electric cables

Simon Still — Wed, 17 Feb 2016 18:43:18 +0000

Posted By: cjardThey aren't that expensive. My CU has 20 ways, all RCBO and it was about 200 quid I think. Sure, a fully populated dual RCD plus 18 MCBs would have been half that, but it's a drop in the ocean of the rest of the build.. What's 100 quid in the face of a Â£20,000 bill for the windows?

Consider that a whole house RCD tripping ruining the contents of the freezer while you're on holiday would probably cost you Â£100 in food..

A good compromise is a split board with a few dedicated RCBO's for important circuits.

I've got the workshop, 'services' (boiler, ventilation, home automation, fire alarm) and kitchen sockets/fridge on RCBO's. The other 8 circuits are split between two RCDs.

A question - the RCD on one of our extension reels is surprisingly warm to the touch. Should it be? I don't notice any heat from the RCBO's in my consumer unit. Seems to work, was a good quality branded reel.

Electric cables

SteamyTea — Wed, 17 Feb 2016 18:50:59 +0000

Is the flex still coiled on the reel? Wholly or partially?

Electric cables

Simon Still — Wed, 17 Feb 2016 20:09:59 +0000

Plug (which is where the rcd is) runs warm when nothing connected to reel.

Electric cables

SteamyTea — Wed, 17 Feb 2016 20:57:43 +0000

It could be failing, who knows.
Has anyone ever pointed an IR Thermometer at an RCD and see if they all warm a bit?

Electric cables

Gotanewlife — Thu, 18 Feb 2016 00:15:31 +0000

Posted By: Simon StillA good compromise is a split board with a few dedicated RCBO's for important circuits.

Yes me too but whilst I put the 40kW wood burner on one I didn't put the kitchen ie freezer/fridge on one - will do now methinks.

Electric cables

chuckey — Fri, 19 Feb 2016 17:58:45 +0000

With respect to conduit in UK houses. In Merton (SW London), there is huge estate of "Blay" Houses built around 1934. More then a thousand houses? They are all wired in conduit, terrible stuff, at T junctions the tube is cut and a sort of open clip is clamped onto the bits of tube. Trying to pull a cable around one of the bend will remove some of the insulation.
FWIW When I added some circuits, I had a situation where there were more wires coming out of a upstairs circuit then were going in. It turned out that the flush, plywood box that the upstairs hall light switch was mounted on, had a junction block behind it. I wracked my brains about where the wires joined , I butchered out the back plywood panel of the switch and found the missing junction, what a relief.
Frank

Electric cables

djh — Fri, 19 Feb 2016 20:22:14 +0000

Posted By: chuckeyI butchered out the back plywood panel of the switch

Which is why current regs are picky about situations like that, I expect. But people still go out of their way to get around them, so clearly there's still room for improvement to make the rules acceptable.

Electric cables

ringi — Fri, 19 Feb 2016 23:46:37 +0000

Part of the issue is that just because a junction box is accessible, it does not mean you can find it unless you know where it is.

Electric cables

SteamyTea — Sat, 20 Feb 2016 08:42:45 +0000

On a new electrical installation there is meant to be a design drawing, so 'not knowing where something is' should be a thing of the past.
Also, comparing the wiring methods from 1934 with today is pretty pointless. Things have moved on.

Electric cables

billt — Sat, 20 Feb 2016 09:48:47 +0000

Posted By: SteamyTeaOn a new electrical installation there is meant to be a design drawing,

Not for the typical domestic installation.

From the approved document:

"for unusually large or complex installations only, detailed plans."

Electric cables

djh — Sat, 20 Feb 2016 09:55:03 +0000

Posted By: ringiPart of the issue is that just because a junction box is accessible, it does not mean you can find it unless you know where it is.

There has to be a label on the front of it if it's not obvious, I believe.

Electric cables

SteamyTea — Sat, 20 Feb 2016 10:47:32 +0000

Posted By: billt"for unusually large or complex installations only, detailed plans."

That has been watered down since I did my Part P.

But this caught my attention. It is only one interpretation of the 17th Edition.
http://www.neweysonline.co.uk/Design-To-17th-Edition/Static.raction

It is the bit about 500mm and impact protection.
I think they added an extra 0, I think it is 50mm.

Electric cables

Ed Davies — Sat, 20 Feb 2016 11:40:15 +0000

Handy list: the point about labelling non-RCD-protected freezer sockets makes sense but had previously escaped me.

Electric cables

SteamyTea — Sat, 20 Feb 2016 12:11:21 +0000

The disconnect time (time for a fuse to blow) used to be longer as well, up to 5 seconds seem to remember.

Seems odd that heavier loads can have less protection, but usually, as the regulations acknowledge, people that use large electrical equipment, have been trained to do so.

Electric cables

Mike1 — Sun, 21 Feb 2016 01:49:55 +0000

Interesting heading about the arc-fault circuit breakers - and strange that they're not mentioned here in the UK. Looks like they also incorporate the functions of an MCBO (which the American market seem to call a GFCI). Found an informative video at https://www.youtube.com/watch?v=ihforRdL-TU

Electric cables

skyewright — Sun, 21 Feb 2016 15:02:29 +0000

Posted By: Mike1Interesting heading about the arc-fault circuit breakers - and strange that they're not mentioned here in the UK. Looks like they also incorporate the functions of an MCBO (which the American market seem to call a GFCI).

Wanting to exactly what RCBO stood for (Residual-current Circuit Breaker with Overcurrent protection) I found there's a lot of international variation among the various types of electrical breakers!

https://en.wikipedia.org/wiki/Residual-current_device

Edit: add emphasis

Electric cables

rhamdu — Wed, 24 Feb 2016 09:45:14 +0000

Ring circuit was a figure of 8, with multiple spurs.
Hidden junctions: wires twisted together in insulating tape, buried in plaster.
Also a lot more twisted joints, under the bathroom floor, where all circuits had been extended to a new CU position.

That was in a house built in the 1970s and altered in, maybe, the 1980s. Not ancient at all.

Electric cables

torrent99 — Wed, 24 Feb 2016 09:59:47 +0000

Posted By: rhamduRing circuit was a figure of 8, with multiple spurs.
Hidden junctions: wires twisted together in insulating tape, buried in plaster.
Also a lot more twisted joints, under the bathroom floor, where all circuits had been extended to a new CU position.

That was in a house built in the 1970s and altered in, maybe, the 1980s. Not ancient at all.

That's pretty shocking! ;-) Not sure that that would change if we banned rings and changed to radial. Mind you it might have helped when the kitchen fitter in my flat (previous owner had it fitted) simply broke the ring in the middle of the kitchen so he could save himself some fiddly wiring. (And also leaving 4 way screw terminal junction boxes & wiring sitting on the possibly wet kitchen floor under the cupboards!)

What's needed is a wiring system that is inherently idiot proof so that it compensates for most DIY blunders.

Electric cables

Ed Davies — Wed, 24 Feb 2016 11:02:28 +0000

Posted By: torrent99What's needed is a wiring system that is inherently idiot proof so that it compensates for most DIY blunders.

Actually, most of the blunders seem to be from professionals [Â¹] though typically trades other than electricians. I suspect the problem is general; trades do a decent-enough job of their own work but take short cuts with the other stuff so kitchen fitters make a mess of electrics and electricians make a mess of airtightness, etc.

An inherently idiot-proof system is no doubt possible but I can't imagine it wouldn't be expensive. Electrics are designed to be cheap, particularly in materials even if it increases labour.

[Â¹] In the widest sense of the word: people being paid to appear to do stuff.

Electric cables

torrent99 — Wed, 24 Feb 2016 14:38:59 +0000

Perhaps what is required is something like the pharmacy model i.e.

Some not very dangerous stuff you can buy in a supermarket/diy store
Some stuff you can only get/do after you have received advice from a pharmacist/certifying electrician.
And some stuff you can only get/do from a doctor/electrician.

I do like the idea of modularization in a structure. Electricians play in their module, plasterers in theirs. Kitchen fitters get to play in the garden ;-), preferably not mine!