Certificate of competency

[rodgearing]

The cpc is not insulated, but it is sheathed in T&E. That is considered adequate when part of a cable.
The cpc is allowed to be smaller in fixed installation cables such as T&E because using the adiabatic equation, it is assumed that the duration of the earth fault current is so short that none of the heat energy produced in the protective conductor escapes before the protective device operates. Although not entirely accurate, it is close enough to satisfy BS7671.

Hope that helps

Excellent answer and true we hope RCDs will operate at 30 or 40 mA but.....the earth in T&E has always been a smaller dia than the current carrying cables longgggg before RCDs ELCBs were considered a necessity and there is still the question of an un sheathed cale. So what you are saying is if you buy a piece of general purpose three core to wire up a a piece of electrical equipment the earthy core is already sheathed in the outer sheath and there fore a seperate sheath is not necessary. But it is sheathed!:wink_smile:

Surely its not that difficult to put a sheath around it? It would take away the necessity to sheath it at either end when making off. Well as an old stager thats my believe.
Having 'leccy'd' in France a lot of what the French leccy's do is far and away better to the way Brits do it and having a sheathed earth of the same diameter as the current carrying cables is one of 'em.
Sorry being pedantic again I'll get me coat!
Fred

 

[trev]

Lol I can remember when last orders was Half nine.

Yee gorrabe aad, I can remember 10:30 being kicking out time when I was about 14/15 but not 9:30

 

[rodgearing]

Yee gorrabe aad, I can remember 10:30 being kicking out time when I was about 14/15 but not 9:30

Yer right. The drinking up bell used to sound at 10:00 and continue till 10:30 this was in the early 70s (I used to live in Clydebank!!)
Fred

 

[ruston]

Yer right. The drinking up bell used to sound at 10:00 and continue till 10:30 this was in the early 70s (I used to live in Clydebank!!)
Fred

Aye I'm going back to when I was a bairn in the 50's , not to far away from you as it happens . I was talking about Scotland though Trev, rang the bell at half nine and drink off before twenty to ten. Then they used to go back to me grannies with the "carryoot".

 

[oldtimer]

Yer right. The drinking up bell used to sound at 10:00 and continue till 10:30 this was in the early 70s (I used to live in Clydebank!!)
Fred

Yep and if you wanted a drink on a Sunday you had to go to a hotel as all pubs were closed aye those were the days

 

[trev]

Yep and if you wanted a drink on a Sunday you had to go to a hotel as all pubs were closed aye those were the days

It all sounds like something from a Dickens novel

 

[ruston]

It all sounds like something from a Dickens novel

Aye but the parties were great.

 

[Des 56]

In Wales,a county could be sunday closed and next door could be open,a pub one side of the river would be 10-30 stop tap,the pub on the other side 11-00

The stampede over the bridge just after 10-30 from the closing pub would have run Bolt a close second

 

[yellowvanman]

Using twin and earth, when stripping back you must always sleeve the earth with green/yellow sleeving in the back box (or whatever)!

 

[rodgearing]

Using twin and earth, when stripping back you must always sleeve the earth with green/yellow sleeving in the back box (or whatever)!

Yes I know that. 50 years experience!
My statement was about the fact that the earth wire in T&E was not already sheathed.

 

[yellowvanman]

Yes I know that. 50 years experience!
My statement was about the fact that the earth wire in T&E was not already sheathed.

Reduces manufacturing costs!

 

[rodgearing]

Reduces manufacturing costs!

OK!!!!!!!

 

[Guitarist]

Yes I know that. 50 years experience!
My statement was about the fact that the earth wire in T&E was not already sheathed.

I have heard many reasons for not insulating the cpc (only the outer part is technically a sheath), and some believe that if you have an exposed cpc, it will provide better protection to the cable itself, should the insulation on a live conductor become damaged. Personally, I think it's the cost factor

 

[pencilpusher]

If it was insulated, it would not slice through the sheathing as nicely when making off :tounge_smile:

 

[rodgearing]

I have heard many reasons for not insulating the cpc (only the outer part is technically a sheath), and some believe that if you have an exposed cpc, it will provide better protection to the cable itself, should the insulation on a live conductor become damaged. Personally, I think it's the cost factor

How was that worked out?
Damaged current carrying cable ie break in insultion, bare cpc, short between earth a live potentially.