Lighting Circuit earth

[bon98uk]

Hi People,

I'm replacing some wall lights which are double earthed. (They are plaster uplighters.) I'm replacing them with metal/chrome fittings. These require an earth connection.

The previous installer has trimmed the earth wires right back into the wall. So there is 'little' slack.

I have following questions/ideas.

I might be able to pull enough slack to make a connection but if not I was either; Going to raise the lights about 2-3 inches up (sorry 50-75mm) up the wall , then make good the plaster. Or solder a length of earth cable (say 3inches) to the short tails and use these.

Of course I also need to check that the earth wire does in fact earth the circuit. So I was going to do a continuity check with the ring circuit earth.

Any thoughts anyone?

regards,

bon

 

[Adam_151]

Hi People,

I'm replacing some wall lights which are double earthed. (They are plaster uplighters.) I'm replacing them with metal/chrome fittings. These require an earth connection.

I take it you mean double insulated?

The previous installer has trimmed the earth wires right back into the wall. So there is 'little' slack.

I trust that you will suitably admonish him?

I might be able to pull enough slack to make a connection but if not I was either

Make sure you don't strain on anything when doing this

Going to raise the lights about 2-3 inches up (sorry 50-75mm) up the wall , then make good the plaster.

Sounds good to me, but if metal capping is used, make sure you deal with the end of it in a suitable way so it doesn't cut into the cable, folding the edge back on itsself to leave a rounded edge is what I quite often do

Or solder a length of earth cable (say 3inches) to the short tails and use these.

As long as you make the joint properly and correctly oversleeve it with heatshrink then thats ok, however you might want to look at crimping it instead, its going to be quicker and you arn't going to be struggling with a hot soldering iron in a tight corner, etc

Of course I also need to check that the earth wire does in fact earth the circuit. So I was going to do a continuity check with the ring circuit earth.

That is a very good idea, for the installer might have pulled a similar trick at the other end of the cable, the method you describe will indeed prove continuity of the earth, but its not a recognised method (but when sparks do it, they are intrested in the resistance value... something that your multimeter won't tell you with any degree of accuracy anyway)


FWIW, the proper methods of checking earth continuity are to use a wander lead from the MET (main earth terminal), and a low ohms meter, the other more popular way (as it gives the R1+R2 value which is asked for on an EIC (electricial installation certificate) )is to use the low ohms meter between live and earth, with the live removed from the fuseway and connected to the earth bar for the duration of the test. Quite a lot of sparks will just stick a loop tester on it, but thats a bit naughty... they shouldn't really use that tester until they have verifiyed earth continuity

 

[JohnD]

If you can solder extensions on, do that. If secure it will be a permanent fix. Slide green & yellow sheathing over the copper and soldered joint when finished.

 

[bon98uk]

Hi guys,

Many thanks to both Adam_151 and JohnD.

I'll try soldering first, I'm pretty competent at that (Electronics Engineer for 30 odd years) and heatshrink the ol' G&Y sleeve. Then do a check.

I must check out the Low ohms meter, I have digital one from Hewlett-Packard (worked for them for a long while) very similar to Fluke. This measures low ohms but does so using internal battery. This might not be able to drive enough current to get the accuracy Adam was referring to.

Any references to the measurement procedure on line? (BTW I know we all use jargon and 'shorthand' ways to describe things but I'm not sure about disconnecting the live and temporarily connecting it to earth!)

regards,

bon

 

[dingbat]

(BTW I know we all use jargon and 'shorthand' ways to describe things but I'm not sure about disconnecting the live and temporarily connecting it to earth!)

If you disconnect the phase conductor from the top of the fuse/circuit breaker and connect it to the earth bar then you can't accidentally energise that circuit until you reverse the procedure. (It's a lot safer than the temporary link method suggested in GN3!)

 

[kai]

You are unlikely to be able to re-energise a circuit, with in effect, a dead short between phase and earth, as the MCB breaker will operate pretty swiftly indeed if you tried to with the phase-earth link in place!!

 

[plugwash]

with modern MCBs i would agree, with plug in units (whether MCBs,cartridge carriers or rewirable carriers) its a lot riskier though (plugging in a carrier against a dead short is very likely to cause some nasty sparks/arcs).