Why do we still have twin and Earth?

Then fiddle about with earth sleeve?

Should be all three inners are insulated, blue, brown and green/yellow.

When will we progress?

Posted By: tonyWhy do we still have twin and Earth?

The only reason the non-earth conductors have insulation is to protect them against shorting to each other or shorting to earth. The earth conductor is already at earth potential so there's no impact if it shorts to earth.

I now like the North American colour codes (which work well for colour blind people). Earth is uncovered, white is neutral and black and/or red are live. So even if you can't see red, you can see that it's not white and anything that's darker than white is live. The colour coding carries over to devices such that the silver screws are for the neutral connection and the brass screws are for the hot connection.

Paul in Montreal.

p.s. plus the outer sleeve insulation is nylon so there's no worry with passing through polystyrene insulation

It does puzzle me that domestic electrical standards still vary so much between countries - particularly within Europe I'd have thought we'd be much closer to a common standard by now.

Posted By: djh

I confess I've never seen a house with the wiring in conduits. It's sort of appealing from an over-engineering neatness point of view, but if I think back to wiring our house I think there are a lot of places where having to route conduits would have been awkward.

My guess is that the reason you never see it in the UK is that it's next to impossible to pull solid core T&E cable through (15 or 20mm) conduit. You can get it through before it's installed but once a conduit has a few bends in it you can't. On the continent, if they're using stranded singles it's much easier.

Posted By: ringiRemember on the continent, their plugs don't have fuses, so each socket has to connect back to the consumer unit with its own cable.

I'm pretty sure that's not the case. They use radials rather than rings but there will be a number of sockets on each radial.

The principle of fuses is that they protect the cable beyond the point of the fuse. A UK radial on 2.5mm will normally have a 20A MCB at the Consumer Unit. That protects the 2.5mm cable between the CU and the socket. The fuse in the plug protects the cable between the socket and the appliance.

Even if a continental radial has a 16A MCB that's still more than many appliance cables could handle. That said, most of the plugs I've looked at in the UK have the wrong fuses in (including extension leads clearly marked as 5A with 13A fuses in the plugs).

Part of the point of plug fuses, though, is to blow quickly. It's fairly easy to have a fault which makes the case of some appliance high voltage but, particularly with the resistance of thin flex, will take a considerable time to trip an MCB (more than a few tens of milliseconds) so delivering enough energy (power for long enough) to stop somebody's heart.

AIUI, this is the reason there's a higher minimum conductor CSA for flexes plugged into radial circuits than there is for rings for with the same fuse or MCB.

Posted By: Ed DaviesPart of the point of plug fuses, though, is to blowquickly. It's fairly easy to have a fault which makes the case of some appliance high voltage but, particularly with the resistance of thin flex, will take a considerable time to trip an MCB (more than a few tens of milliseconds) so delivering enough energy (power for long enough) to stop somebody's heart.

AIUI, this is the reason there's a higher minimum conductor CSA for flexes plugged into radial circuits than there is for rings for with the same fuse or MCB.

So continental circuits just don't have any protection over this type of fault? A 16A or 32A MCB isn't going to make any difference there is it (or is that situation covered by the RCD in both countries now?)

A working RCD will trip if the current going out in the L is more then what is coming back in the N. Therefore it will trip if someone touches a live case.

If the case is earthed the RCD will trip as soon as the case becomes lives.

However RCD do fail more work more often, hence they should be tested every 3 months.

Broadly, a cable (ie 3 wires) costs the same as a conduit with 3 wires run in it. I only use 4 colours brown, Blue, Earth and Grey for switch lives but there about 10 colours here and each electrician has his own 'code' for what colours do what - saves on labelling!! If it's going in a wall or in screed I always use a conduit and separate cables and my main hub on each floor has 5 or so radials in it so one earth and 5 pairs of N and L with lighting all 1.5 and sockets all 2.5mm2. I use 16A MCBs for sockets and 6amps for lighting and then make enough circuits to allow this but I didn't do any sums. I have a good smattering of UK sockets about and lots of UK switched fused spurs, Over here to create a switched fused socket you have to use a 3 gang box and and connect up a double pole switch to a fuse to a socket (circa 25 Euros all in) - only did it once as extra protection for my whole house water pump. I made a lot up as I went along - I put the electric oven on a unique MCB (even though it doesn't draw that much) and put separate radials in for the kitchen, my sons bedroom (partly so I didn't have to turn him off when i was working on that floor).

This is our forever home, I just hope if I ever sell (or my son comes to sell!) so many years have passed that there won't be any problems 'cos it's all done DIY - no supervision or documentation beyond the 3 consumer units. I was able to buy the house with outrageous in-situ electrics so I hope this indicates it will all work out fine in the end.

A RCD and a fuse/MCB do different things.

They go to the 'off' position under a fault condition.
Not the same as failing to 'off'.

Posted By: djhit's fairly common that a fuse in the plugtop will blow without tripping the RCD, even without the RCD being faulty.

Exactly right - no fault to earth just fault from live to N making for too much current and blowing fuse, if fuse wasn't there then either there would be catastrophic failure of electrical elements breaking bad circuit (and fire invariably) OR the consumer unit MCB would turn off - but this type of fault would never cause the RCD to trip. Though it might as melted wires and arcing caused some current to flow to earth, except perhaps not in a double-insulated laptop.

DIYers - You need to know these things if you do any electrics; they are on page 1 of the things DIYers must know before touching a screwdriver.

Posted By: ringiA RCD will not trip on a L to N fault, or a overload.

The ones we have over here will trip on both ground faults and over-current faults. The breakers we have are a combination of over-current and earth-leakage (or arc fault detection). We don't have separate RCDs except for special sockets that go in places like bathrooms or outside where the overall circuit doesn't have earth fault detection. In my bathroom the socket has RCD protection and all the lighting circuits are fed from the downstream output of the RCD so that all the switches in the bathroom are protected rather than having the whole radial circuit that the bathroom sits on having an RCD breaker.

Paul in Montreal.

<blockquote><cite>Posted By: SteamyTea</cite>An RCD failure is when the actual unit fails, so it may be unable to detect the imbalance or may be physically impeded from reacting to the imbalance. Then it may fail in either the on or the off position.</blockquote>

This is why they (should) have a test button that should be tested regularly.

RCD 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"?

Now with mandated arc-fault breakers, the two functions (earth leakage and arc detection) have been integrated into one circuit breaker device, such as: http://www.schneider-electric.us/en/product-range/62274-qo-dual-function-circuit-breakers/

See also http://download.schneider-electric.com/files?p_Reference=RP19520116&p_EnDocType=Brochure&p_File_Id=1713692785&p_File_Name=Square+D+Advanced+Function+Breakers.pdf which gives more details about arc faults etc.

Paul in Montreal.

Arc Faults for some reason don't seem to be common in the UK.

It will be very hard to damage "twin and earth" in a way that gives a N/L fault without getting a L/E fault. But I would still expect Arc faults on cables attached to plugs.