3-stranded cable (again!)

[Careful_Bodger]

Is there an on-line source with the technical/performance specs for the old imperial cable types, viz: 3/.029, 3/.036, etc.

Since I (or rather my lights) seem to be pulling current through some I thought it'd be prudent to know what it used to be rated at. Dimensions (inner/outer) would be useful for positive identification.

Have tried a web search, but without obvious success.

Cheers All

 

[Paul_C]

I don't think I have the overall dimensions anywhere, but I can scan the appropriate tables from the 14th edition IEE Regs. if you like: Current ratings, voltage drops, etc.

 

[Careful_Bodger]

Good Idea Mr _C ,

Could you post the tables to the Reference section?

Thanks muchly!

 

[Paul_C]

Done.

I've posted links to the scans in the reference section rather than include the images directly: The scans are fairly wide to make them reasonably legible and I didn't want to make the thread too wide or slow to load.

 

[kai]

Is there an on-line source with the technical/performance specs for the old imperial cable types, viz: 3/.029, 3/.036, etc.

Since I (or rather my lights) seem to be pulling current through some I thought it'd be prudent to know what it used to be rated at. Dimensions (inner/outer) would be useful for positive identification.

Have tried a web search, but without obvious success.

Cheers All

Still using the old imperial cables?
Well past their safe operating life - and no earth on the lighting circuit - a full rewire looks likely to be needed for safety.

 

[dingbat]

Still using the old imperial cables?
Well past their safe operating life - and no earth on the lighting circuit - a full rewire looks likely to be needed for safety.

I did a PIR last month on an installation that dated from 1958. All VIR cables (except the lights, which had been rewired in PVC T & E in the eighties). Every single circuit had insulation resistance readings in excess of 500 Mega-ohms in every combination. The earths were more than adequate for their purpose, with Zs readings as good as any new installation. Inspection showed perfect terminations in accessories and the only embrittlement of insulation was close to the ends of the conductors in the CU.

 

[Careful_Bodger]

Kai,

Please see my previous post for details of the old cable - it does indeed have a CPC......

I have uncovered some 3 stranded twin & earth in a lighting circuit, with red and black PVC insulators, bare solid CPC, and white PVC outer sheathing. From the outside it looks very much like 2.5mm T&E.

Is this a Bad Thing?

Is this Imperial 3/0xx, or not??

 

[Paul_C]

Still using the old imperial cables?
Well past their safe operating life - and no earth on the lighting circuit - a full rewire looks likely to be needed for safety.

Not necessarily, and certainly not in the case of PVC-insulated cables.

There was also an overlap of a few years before metric cables were introduced but when installations to the 14th edition Regs. did require an earth on lighting circuits, so you can't make an absolute statement that Imperial cables means no earth. Besides, some houses were wired with lighting earths before the Regs. demanded it anyway.

 

[kai]

That's news to me!

I couldn't think, especially in those days, why on earth someone would want to install anything that was not required by the Regs, into a wiring system...

 

[Paul_C]

Perhaps I should have said "before the Regs. demanded it for all lighting circuits."

The pre-1966 Regs. didn't give a blanket exemption from earthing on all lights. Some homes would still have needed earths on lighting circuits to comply with the 13th edition rules.

The relevant exemption from earthing exposed metalwork was in 403(ix):

Lighting fittings using filament lamps installed in a room having a non-conducting floor, mounted at such a height that they cannot readily be touched and are out of reach of earthed metal.

So an earth would still have been a requirement for wall lights not mounted out of reach, or for a fluorescent light in a kitchen for example.

Note too that metal switches were required to be earthed as well.