Earth sleeving in sockets?

[pcboffinuk]

ok, this is probably a silly question, so feel free to give a silly answer

Firstly, I am aware of the regs regarding earth sleeving in sockets/switches etc. and always put it in place.

However, I like to know the reasons behind rules, and I wonder if I am missing something obvious....

I can see an argument for identification of the earth wire to ensure it is obvious which one it is, although in a standard domestic setting I can't see this being a problem.

However, with regards to safety, I can also see an argument that it would be better to have the earth wire bare. If a phase/neutral wire was to come loose in a socket, it would be more likely to touch a bare earth wire and therefore trip the breaker/blow the fuse, which is surely "a good thing"?

So can someone enlighten me as to what I'm missing, or is it just one of those rules I follow and not think too hard about?

Gavin

 

[securespark]

For the very same reason, it is a bad thing to leave it bare. You want to avoid short circuits!

 

[pcboffinuk]

Agreed avoiding short circuits is a good thing, but only in normal usage...

I see the point, just that I can also see the point that in a fault scenario (a phase wire comes loose, breaking the ring) blowing the fuse might be advantageous, if annoying...

Having said that, a socket with two ring cables and a spur crammed into a back box might well be very likely to short circuit through wires touching, so I'll concede your point

Any advance from anyone else?

Gavin

 

[con1_uk]

Another stupid question

Why don't they cover the earth like the other cores in manufacturing?

 

[Spark123]

The only logical reason I can think of is cost.

 

[pcboffinuk]

Another stupid question

Why don't they cover the earth like the other cores in manufacturing?

I did ask this question on a course, and the tutor couldn't come up with an answer, but thinking about it afterwards it makes sense - if the cable is cut and the phase insulation damaged it increases the chance of it shorting to earth and tripping the breaker...

But that is the same argument as having the earth cable bare in sockets, so I guess cost is a more likely answer

Gavin

 

[Steve]

To make it easy to strip T+E? Was T+E designed so the earth core could be used to strip it? Or is there another "approved" method?

 

[RF Lighting]

Go wash your mouth out young man.

You are not supposed to bare back t&e by pulling the earth, as this can stretch the wire, reducing the CSA, and therefor the effectivness of the earth.*

You should strip t&e with a knife, by carefully slicing straight down the middle of the cable, without damaging the insulation on any of the insulated conductors, this method does take a bit of practice but is much easier once you have got used to it.




*I know loads of people do it but is still wrong.

 

[Steve]

Either way, if the earth core were insulated, it would make it a lot trickier.

Then again, flex has the same problem.

 

[RF Lighting]

Once you have mastered using a knife it is quite easy to strip the old 70s twin cable (no earth) without touching the insulation of the conductors, just like the old pros used to do back in the day

 

[plugwash]

You are not supposed to bare back t&e by pulling the earth, as this can stretch the wire, reducing the CSA, and therefor the effectivness of the earth.*

has anyone actually measured this effect? i'd imagine its pretty negligable.

p.s. what methods do people use to strip 3 core flex without damaging the individual cores?

 

[ricicle]

I was taught the cheesewire method at college.You would have to put a hell of a strain on the cpc to stretch it
I was also taught to strip flex by nibbling along the length with snips (no double entendres Secure )

 

[SparkyMarky]

p.s. what methods do people use to strip 3 core flex without damaging the individual cores?

I score it very lightly with a knife (mainly to give myself a line to work to), then bend it around my finger to put the sheath under tension. Then with hardly any pressure (almost just resting a sharp knife on it) I just deepen my score mark until the inner cores become visible. Bend the cable the other way, repeat the process on the other side, then just pull the sheath off the cable to seperate it completely. Job's a good un!

 

[mdbalson]

You are not supposed to bare back t&e by pulling the earth, as this can stretch the wire, reducing the CSA, and therefor the effectivness of the earth.*
*I know loads of people do it but is still wrong.

This is how they are teaching people how to strip T+E, at the college I am at, do the C+G 2330 in elec. install. (and at other colleges)

You should strip t&e with a knife, by carefully slicing straight down the middle of the cable, without damaging the insulation on any of the insulated conductors, this method does take a bit of practice but is much easier once you have got used to it.

They do not teach this method, because of Health & Safety, incase someone cuts themselves with the knife.

 

[kevnurse]

The earth conductor in T&E lies tightly against both of the other 2 conductors. Thus any stray current across either of the 2 insulating sleeves, for whatever reason, will immmediately go to earth and hopefully activate the circuit protection. This is why it is not insulated within the cable.

Once the 3 conductors are spread out in the terminal box, the earth conductor cannot protect the 2 other conductors like it does within the cable. The earth conductor then protects the loads and as such it is a potential conductor in an exposed space within the box. It needs insulation for that purpose.

all IMHO.