Why isnt earth sleaved?

[turningtim]

I know this may sound a daft question but....

Why isn't the earth core of T&E sleeved like the other two, it needs have a sleeve at every point its visible so why not build it in like flex, is it the bulk, the thermal properties or????

(not a sparky as you can guess just curious)

 

[sblakey1]

i would assume that if you were to ever have failure of the insulation of live/neutral "with in" the T&E cable it will leak into the unsheathed earth cable and maybe trip the RCD/RCBO/MCB

 

[turningtim]

perhaps -but isnt that more likely to happen with flex on a portable appliance?

 

[Spark123]

Twin and earth isn't flex. It is a fixed installation cable.
The CPC isn't sleeved because it doesn't need to be and it is cheaper not to.

 

[sblakey1]

quite possibly with the movement of the flex , however people dont hang pictures or screw skirting boards into flex from lampholders..

 

[sblakey1]

or the cheaper reply is sufficient!

 

[Steve]

It isn't sheathed because then you can pull it with pliers to strip cable easily and quickly.

 

[Click-Sure]

No, not at all...

edit:

woo! 1001'st post!

 

[Taylortwocities]

woo! 1001'st post!

 

[securespark]

That woman in the white dress looks like my Granny...

 

[Taylortwocities]

Wow, you must be unbelievably young then

 

[mattylad]

What on earth! is the guy 4 rows behind the woman doing?

 

[ban-all-sheds]

Cutting cheese?

 

[Diyisfun]

Back to the topic..
Its about cost & there not being a need. Anyone who has been involved with manufacture would know that.
There are then other advanges, like easy to strip.

 

[ericmark]

As well as cost there is also size. The flat twin and earth is designed to be as inconspicuous as possible and was a follow on from the lead cable it replaced where the lead sheaving was the earth. Some was made in early days without earth and the grey colour makes it look similar to the lead type it replaces. With a conducting outer sheaving having a non insulated earth core was an advantage as it would insure if there was a break in outer the inner earth wire would earth any non attached bits.
As time has gone on new cables have been developed to replace the flat twin and earth and they have gone back to the idea of having a conducting outer sheaving.

this shows the new Ali-tube cable again with bare earth so it can contact the Ali-tube and earth the tube so insuring anything penetrating the cable will cause the protective device to trip. Although I did read that the protective device needs to be B type for it to insure it trips rather than burn a clearance hole in Ali-tube. But not sure on this.