lighting circuit with no earth

You would be best rewiring. It's a bungalow, so not a big job. The walls drops are likely in conduit (certainly most that age are). It's a days work for a sparky, perhaps a weekends work for a DIYer.

 

As lectrician says deffo partial rewire. You need a 4 mm earth , by the time you've faffed about with that!!

 

Yea I would like to know too.

 

Unprotected conductor, wouldn't think ur going to run it in conduit! 2.5mm if protected 4mm if not

 

Why so? The only time I can think this would apply is for bonding where the bonding cable is underground. Got a reg some where?

 

According to wiring regs. the minimum size for an un-protected cpc is 4.00mm. It does seem daft I know especially on a lighting circuit fused at 5 amps and where the cable is under the floor or above a ceiling where there's nil chance of it becoming damaged. I must admit I've used 1.5 mm on a few occasions!

 

Sen mate, that don't make sense. If the min size is 4mm unprotected then how come we have twin and skin with cpc much smaller than that? Surface mounted twin is no less liable to damage than a single 4mm cpc...

 

It does make sense. It is to protect the conductor as it is not mechanically protected.

Incidentally the cpc in twin and skin is mechanically protected (the sheath is mechanical protection).

 

So a sheathed single cpc could be less than 4mm?

 

Maybe if it was insulated AND sheathed, although there's nothing to say that in the regs. as far as I know.

 

Sorry guys I'm not convinced. Check out this

https://www.eca.co.uk/filelibrary/download/?FileID=1284

Only thing it say's about cpc size is if it's buried. Other than that an adiabic is fine.

Unless someone can come up with some regs and a bit of back ground I'm not buying it.

 

Also this...

http://www.select.org.uk/downloads/ESC Best Practice Guide No. 1 - Issue 2.pdf

No mention of minium cpc size anywhere in the lighting ctts section.

 

Col - ssssshh otherwise there will be a new edition of the regs out. more books, courses, dvd's

 

OK, this is the red book (The only PDF I have, paper copies at work).

543 PROTECTIVE CONDUCTORS
543.1 Cross-sectional areas
543.1.1 The cross-sectional area of every protective conductor, other than a protective bonding conductor, shall
be:
(i) calculated in accordance with Regulation 543.1.3, or
(ii) selected in accordance with Regulation 543.1.4.

Calculation in accordance with Regulation 543.1.3 is necessary if the choice of cross-sectional area of line conductors
has been determined by considerations of short-circuit current and if the earth fault current is expected to be less
than the short-circuit current.

If the protective conductor:
(iii) is not an integral part of a cable, or
(iv) is not formed by conduit, ducting or trunking, or
(v) is not contained in an enclosure formed by a wiring system,

the cross-sectional area shall be not less than 2.5mm² copper equivalent if protection against mechanical damage is provided, and 4mm² copper equivalent if mechanical protection is not provided (see also Regulation 543.3.1).
For a protective conductor buried in the ground Regulation 542.3.1 for earthing conductors also applies. The
cross-sectional area of a protective bonding conductor shall comply with Section 544.

 

Strange none of this is mentioned in the select guide seeing as it's pretty integral.

 

It's really nothing new. It has been in the regs of several jurisdictions for as long as I can remember.

 

This is where i say I knew I was rite, been the case for years far as I can remember. I know it's overkill but we don't rite the regs.

 

Well done Lec, I knew it was there somewhere!