Two core imperial cable (no earth)

[bongos]

Was helping out with a CU change at a large Victorian house last week. Both upstairs radials were supplied by two core pvc clad cable. There was no earth core in the cable, just stranded red/black. They are not wired in conduit.

It look like tinned conductors although having never seen these in the flesh before i'm guessing. The cable looked slightly larger than 2.5mm² t+e but not quite as large as 4mm² t+e.

When would it have ever been acceptable to wire s/o without an earth?

 

[dannyboi2003]

I hope the supply to those sockets is now disconnected or re-wired?

 

[timtheenchanter]

IIRC many moons ago, there were 2pin sockets that had no earth.

 

[davelx]

Aye, when I were a lad we had two pin 5A and 15A sockets. I can remember plugging the transformer for my Horby 00 trains set (3 rail version) into them

 

[Paul_C]

It look like tinned conductors although having never seen these in the flesh before i'm guessing.

That was the usual form for Imperial cables - Tinned copper strands. In later years there were some aluminum conductors used for a short time though, which can appear similar at first glance.

When would it have ever been acceptable to wire s/o without an earth?

Pretty much only for the 2-pin sockets mentioned already. The 5A types were still in fairly widespread use into the era of PVC-sheathed cable, but the 2-pin 15A types were obsolete by then.

The cable looked slightly larger than 2.5mm² t+e but not quite as large as 4mm² t+e.

It was probably 7/.029, which works out to about 2.9 sq. mm equivalent.

Here's the relevant table from the 14th edition of the Regs. which shows the cable ratings:

Untitled

• Paul_C
• 20 Apr 2010
• 1

Approximate conversions on the sizes:

1/.044 = 0.97 sq. mm
3/.029 = 1.3
3/.036 = 1.9
7/.029 = 2.9
7/.036 = 4.5
7/.044 = 6.5
7/.052 = 9.4
7/.064 = 14.5
19/.044 = 19.4
19/.052 = 25.8
19/.064 = 38.7

 

[sparkwright]

What type of sockets does the wiring serve?

There was a practice of running a separate bare earth wire to sockets, along the 2 core cable.

 

[bongos]

They served BS1363 socket outlets. Both were radials for first and second floors although I think the spark that intsalled the old CU must have thought it a ring final. It was on a 32a mcb anyway...

There was a practice of running a separate bare earth wire to sockets, along the 2 core cable.

There was a bare stranded conductor separate from the two core which entered the CU also but this didn't provide any earth path from the sockets. It might have done at one time though I suppose.

Can anyone put a rough age on these old circuits?

 

[RF Lighting]

Sounds like quite an unconventional setup.

I've never seen sockets supplied in two core cable as new as PVC, and even sockets supplied in lead, VIR or rubber cable still tended to be supplied with an earth.

Maybe they were wired in lighting cable? This was made as 2 core with plastic insulation, (I'm not certain, but I don't think it was actually PVC), and IIRC it went out of production in the 1970s

 

[sparkwright]

So are the old cables in use, and some/all of the sockets have no earth?

Or has it all been replaced?

Just curious if you've looked behind some of sockets, and how they are terminated.

Do the sockets look quite old, or do you think they are fairly recent replacements?

Without actually seeing the cable you have described it possibly dates from around 1950.

 

[bongos]

I've never seen sockets supplied in two core cable as new as PVC, and even sockets supplied in lead, VIR or rubber cable still tended to be supplied with an earth.

I've said PVC because that's what it most looks like. Doesn't look like VIR but i've not seen that much of the stuff. The red and black sheathing on the cores is different to usual though. A really stretchy plastic like matter. Sorry my description is not very good RF.

Maybe they were wired in lighting cable? This was made as 2 core with plastic insulation, (I'm not certain, but I don't think it was actually PVC), and IIRC it went out of production in the 1970s

There are lighting circuits in the install in what looks like the same type of cable also without an earth. These are smaller csa. Looks like the imperial equivalent of around 1.5mm² t+e.

So are the old cables in use, and some/all of the sockets have no earth?

None of them have any earth. The homeowner's father is a retired spark and couldn't see the concern of no earth at any upstairs socket outlets. But then he said he got out of the game because they brought in testing and too much paperwork... Despite "dad's" advice the homeowner still wants them rewired.

Just curious if you've looked behind some of sockets, and how they are terminated.

Unfortunately not. If I end up helping out on the rewire then i'll have a good look.

Do the sockets look quite old, or do you think they are fairly recent replacements?

A mix. Some look ancient but there are recent additions. Interestingly they had some electrical work completed in the bathroom a few years ago. An extractor fan was put in but as there was no earth in the lights the spark spurred a supply in 2.5mm² t+e from the 32A protected radial to the extractor. No local isolation or fusing down. But then he also "rewired" the sockets after finding no earth...