Twin and Earth. (insulated earth)

AndyPRK · 31 May 2019

This has been discussed before, but I thought you may which to see some twin and earth where the earth already comes sleeved. Used in Ireland

watch from 4 minutes onward.

Also shower priority unit

crystal ball · 31 May 2019

Lost count of the number of hours wasted coming down ladders or trailing to the van for a bit o sleeving, used T&E with insulated CPC in OZ in the 80s, far better

Risteard · 31 May 2019

If anyone wants to buy Irish Standard 201-4 cable then I can sell it at a price that is generous (to me).

nitro23456 · 1 Jun 2019

This guys videos are always excellent, he just speaks a bit fast for my pea brain so end up having to watch bits twice.

mikeey84 · 1 Jun 2019

I may regret the 4 page discussion that will entail from this question, but I've missed previous threads on the subject.

Why is the earth not sleeved in t+e?

JohnW2 · 1 Jun 2019

mikeey84 said:
I may regret the 4 page discussion that will entail from this question, but I've missed previous threads on the subject. ... Why is the earth not sleeved in t+e?

Possibly just to save money.

However, there is one theoretical safety advantage in having a bare CPC - in that, in the event that something (e.g. a nail) penetrates the cable and comes into contact with the Live conductor, a bare CPC makes it even more likely that the penetrating object will also come in contact with 'earth', thereby causing a protective device to operate, clearing the fault.

Kind Regards, John

mikeey84 · 1 Jun 2019

Cheers John.

FrodoOne · 1 Jun 2019

crystal ball said:
Lost count of the number of hours wasted coming down ladders or trailing to the van for a bit o sleeving, used T&E with insulated CPC in OZ in the 80s, far better

It has been a requirement in Australia since (about) 1966 that the Earth conductor in all Twin and Earth cables be insulated to the same standard as the Line and Neutral conductors. (https://en.wikipedia.org/wiki/Electrical_wiring)
In addition, for all cables the Earth conductor is always "stranded".

Further, while cables with solid conductor over 1 mm CSA are/were available, virtually none is now sold - since cables with stranded conductors (although slightly more expensive to purchase) are so much easier to work with.

We in Australia find it incredible that in the UK 2.5 mm CSA solid conductor cable is still used!

Of course in North America the equivalent solid conductor cable (AWG 12) is (unfortunately) necessary, because of the fact that the screw connections used on most of their switches and socket outlets require that a single conductor be twisted under the head of a screw.

EFLImpudence · 1 Jun 2019

Conversely, what is the electrical benefit of insulating the CPC throughout the cable?

john4703 · 1 Jun 2019

He talks about the problem of sleeving when terminating the cable. I'm sure that back in the 1950s I terminated twin and earth without using a sleeve on the earth. Does the sleeve do anything?

EFLImpudence · 1 Jun 2019

john4703 said:
Does the sleeve do anything?

I have several times asked what it's actual purpose is supposed to be.

Replies have said it stops the CPC touching anything that it should not. Vice versa is sort of its purpose and might be useful.

JohnW2 · 1 Jun 2019

EFLImpudence said:
I have several times asked what it's actual purpose is supposed to be. Replies have said it stops the CPC touching anything that it should not.

In many situations (e.g. like a JB, with 'strain restrained' cables), I can't really see the point.

However, as I've said before, I can see some point in the case of accessories mounted on back boxes, since there is often no telling how the conductors (including a bare CPC) are going to bend and crumple up when they are pushed back into the back box with the accessory, so it's not impossible that they would touch something that they shouldn't.

Kind Regards, John

winston1 · 1 Jun 2019

FrodoOne said:
We in Australia find it incredible that in the UK 2.5 mm CSA solid conductor cable is still used!

It came in with metrication around the end of the sixties. Don't know why. At the time sparks said they preferred the prievous stranded 7/029.

winston1 · 1 Jun 2019

john4703 said:
He talks about the problem of sleeving when terminating the cable. I'm sure that back in the 1950s I terminated twin and earth without using a sleeve on the earth. Does the sleeve do anything?

Is the sleeving actually a requirement, or is it something that is just done? It certainly was not done back in the 50's judging by old imperial installations.

donrkebab · 1 Jun 2019

Sleeving is required because:

522.5.2 Dissimilar metals liable to initiate electrolytic action shall not be placed in contact with each other,
unless special arrangements are made to avoid the consequences of such contact.

522.5.3 Materials liable to cause mutual or individual deterioration or hazardous degradation shall not be
placed in contact with each other.

For the same reason, bare copper sheathed cables must not be installed on galvanised metalwork

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Twin and Earth. (insulated earth)

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