"John Rumm" wrote in message
o.uk...
Harry Bloomfield wrote:
John Rumm wrote :
To check the earth continuity you can disconnect the live at the circuit
breaker or fuse, and temporarily join it to the earth wire for the
circuit.

Which would still leave the neutral connected and the neutral connected
to earth at the sub-station. One or more lights in the circuit left on
and the live will have at least some sort of connection to earth - enough
to cause some confusion when using that method.

Yes, sorry I did not explicitly say - turn the CU off at the main switch.

(personally I would disconnect all the circuit wires and twist them
together - then using a low ohms meter one can do a number of other checks
as well as establish the circuit layout a bit quicker)

The using a DMM on ohms range measure the live to earth resistance at
each lighting position (or switch). You should soon be able to find
where in the circuit you have a disconnection. Chances are it will be at
a ceiling rose somewhere - leaving the remainder of the circuit with a
floating earth.

There were two standard methods to wire the lighting circuits using T&E.
The current method is from the Dis-board then lopped into each ceiling
rose in turn, then down from the ceiling rose to its associated switch.
The older method was similar to the above, but a joint box was used as
the central connection point for each section of the circuit.

There are plenty more than two out there! Loop in is the most common, but
JBs and looping through the switch positions is are also fairly frequently
found.

If wired using the later joint box method it could well be that the break
in the earth is at one of these under floor joint boxes.

Could be - but you should still be able identify in what section the fault
is from tests on what you can get access to at the light and switch
positions.

--
Cheers,

John.

Guess what job I am doing later in the week?

I got a phone call off a bloke complaining the metal backbox in the new
bathroom shaver point that he has fitted lights up his neon screwdriver. His
further tests showed that the same happens in one of his bedroom lightswitch
metal backboxes.

I am glad that he has taken his girlfriend away for a long weekend as his
words "You do not get a shock when you poke the backbox with your finger"
did worry me a little.

My first test will be an earth loop test on the new shaver socket.

My second test will probably be a resistance reading between the shaver
backbox and any available earth (eg a screw at socket front)

Cheers

Adam