Connecting un-used conductors to earth

[sparkwright]

Connecting un-used conductors to earth.

This practice is often mentioned on the forum, but I've yet to see it in real life.

And if I did see it in real life I would feel compelled to check it out.

Yet if each conductor was connected to a connector block and tucked away, possibly I wouldn't be as concerned.

Do you sleeve the un-used conductors green and yellow?

What is everyone's thoughts on this practice?

 

[JohnW2]

Connecting un-used conductors to earth. This practice is often mentioned on the forum, but I've yet to see it in real life. And if I did see it in real life I would feel compelled to check it out. Yet if each conductor was connected to a connector block and tucked away, possibly I wouldn't be as concerned.

In my limited experience, I've never seen it, either, but I've seen plenty of cables ending in ('separate terminal') connector blocks or JBs. I suppose those who do it feel that they are thereby demonstrating the the cable in 'dead' - whereas a dead-end cable terminated ('separate terminals') in a connector block or JB could be live. I suppose the other 'blue moon' possibility is that there could be an undetected branch from the cable and if it ever was energised, the joined L/N/E would cause a protective device to operate!

Having said all that, I don't think you'll ever find me doing it!

Do you sleeve the un-used conductors green and yellow?

.If they were not being used as CPCs that would probably be non-compliant with the regs!

Kind Regards, John

 

[westie101]

I've seen it done at 11kV where only two phases are energised, trouble was it caused interference with a BT cable so the third conductor was energised.

Newly laid and disconnected cables at all voltages have all the conductors connected to earth as a aid to identification in the future. The id is done by passing a signal down two conductors that can be detected outside the sheath as it is only 2 of the 3 conductors the signal will vary according to the lay (twist) of the cores
For HV the id will be proved by spiking the cable

 

[kai]

It is actually safer to connect the unused phase core of a spare circuit to earth at the consumer unit end.

This prevents the breaker being switched on inadvertently and energising the spare cable run, and helps with one of the earthing tests, should the circuit ever be needed again, say for an immersion heater / electric shower etc.

Whenever any circuit is introduced, or re-energised after a period of disuse, the circuit's phase core needs to be connected to the earth block of the consumer unit in order to perform the CPC continuity test. (R1+R2 to the electrician).

 

[EFLImpudence]

I have recommended it and have done it.

New (replacement, so notified ) consumer unit.

Cable connected to MCB,N&E - no idea where it went or what it used to supply and no way of determining where it goes after entering the wall.
No unused accessories.

Connect all conductors together at earth bar. All safe.

If, one day, someone discovers the other end they will quickly discover continuity between all conductors and to earth so must be the cable in the CU.


If a disused cable cannot be removed from a wall then connecting conductors at both ends would ensure safety and if discovered mid-run it can be determined that it is not used.

 

[AndyPRK]

Humm I wonder how many ppl on discovering an unused cable test to see if all conductors are shorted together.

 

[JohnW2]

It is actually safer to connect the unused phase core of a spare circuit to earth at the consumer unit end.

That's fair enough, as a matter of convenience as much as anything else, but I didn't really imagine that sparkwright was really thing in terms of inside CU's - but maybe he was!

This prevents the breaker being switched on inadvertently and energising the spare cable run ...

True, but so would connecting it to anything else (e.g. a bit of connector block) other than the MCB. However, as above, the earth bar is probably the most convenient place in a CU.

Kind Regards, John

 

[JohnW2]

Humm I wonder how many ppl on discovering an unused cable test to see if all conductors are shorted together.

Unless they are crazy, I wouldn't think that they would need to test, since they would/should have ascertained the answer 'by inspection'. It would take a pretty daft person to energise one end of an 'unused cable' without first having investigated what was happening at the other end of the cable!

Kind Regards, John

 

[AndyPRK]

This was what I was getting at, not reenergising the circuit

If, one day, someone discovers the other end they will quickly discover continuity between all conductors and to earth so must be the cable in the CU.

 

[westie101]

If, one day, someone discovers the other end they will quickly discover continuity between all conductors and to earth so must be the cable in the CU.

And possibly not another cable on another circuit

 

[JohnW2]

This was what I was getting at, not reenergising the circuit

If, one day, someone discovers the other end they will quickly discover continuity between all conductors and to earth so must be the cable in the CU.

Oh, I see - yes, that would probably be the first stage (well, second, after 'testing for dead') of confirming that one had found the two ends of the same un-used cable - but I would expect to have to, myself, connect conductors together at the time to do that! EFLI's 'test' would not be reliable for 'identification' if someone had been joining L/N/E on unused cables all over the house! In such a situation, the stages I would use would be as follows (after locating two cable ends, which I believed were the two ends of an un-used cable):

1...'test for dead' at both of the 'ends' I had found'.

2...confirm that there was no continuity between (separated!!) conductors at both ends.

3...join the conductors at one end and confirm that there was a suitably low resistance between conductors at other end.

4...depending what I had to hand, connect either a, say, 9V battery or a medium-value resistor between L&N and then measure (volts or ohms, as appropriate) at the other end. You would have to really scrape the barrel of the 'vanishingly improbable' to think of a situation in which the voltage or resistance would be correctly measured at t'other end if it were not the same cable

Kind Regards, John

 

[Risteard]

Do you sleeve the un-used conductors green and yellow?

I do.

 

[sparkwright]

There would be more situations where an un-used cable wouldn't come directly from a consumer unit, as already discussed.

I would imagine there could be instances where an un-used cable may cause problems if all conductors are connected to earth, particularly if the un-used cable is in fact connected to a supply.

I recall an occasion where a cable was wrongly connected to a very hidden junction box, and it was 'impossible' to disconnect it. At the switch end of the cable the brown and blue were put in blocks to separate them completely, thought may as well as leave the earth connected. However, the strange fault didn't allow that earth wire to be connected.

Obviously this doesn't count as an un-used cable, as one end was still (wrongly) connected.

But I have to wonder if it's safer/less possible aggro to simply put each single conductor separately into connector blocks.

Though connecting them to earth should stop them having a voltage on them, is this causing confusion for the next man, should we worry if the earth connection was to get broken, and do we want these 'foreign' cables connected to an otherwise good electrical installation?

 

[sparkwright]

I don't think there's ever been a case on the forum where a poster has found a cable with a red, black and it's earth stuffed in the earth terminal of an accessory.