Hi All,

Before anyone says look out, its ok the power is off for the part of
the circuit I need to test... And, naturally, I only want to test it
whilst its off.

Part of a lighting circuit has been shown (I assume) to be shorting -
a qualified electrician has disconnected the part that is causing the
problem. But they were unable to tell where the fault actually is
located.

With the problem part now safely isolated and off, what equipment can
I use to locate the fault by a process of elimination? ie. removing
switches or disconnecting sections of the circuit until the bad part
is pin pointed ?

I have a multi-volt/amp/resistance meter and I assume that would that
show me when a direct short is occurring? I suppose everything in
circuit would need to be disconnected ie. light bulbs taken out just
in case the 2 way switch is actually in the on position.

Any advice ?

Tom

On Oct 19, 7:18*pm, Tom wrote:
Hi All,

Before anyone says look out, its ok the power is off for the part of
the circuit I need to test... And, naturally, I only want to test it
whilst its off.

Part of a lighting circuit has been shown (I assume) to be shorting -
a qualified electrician has disconnected the part that is causing the
problem. But they were unable to tell where the fault actually is
located.

With the problem part now safely isolated and off, what equipment can
I use to locate the fault by a process of elimination? ie. removing
switches or disconnecting sections of the circuit until the bad part
is pin pointed ?

I have a multi-volt/amp/resistance meter and I assume that would that
show me when a direct short is occurring? I suppose everything in
circuit would need to be disconnected ie. light bulbs taken out just
in case the 2 way switch is actually in the on position.

Any advice ?

Tom

Assumptions tend to be wrong in these sort of situations.
http://wiki.diyfaq.org.uk/index.php?title=Trace
and maybe
http://wiki.diyfaq.org.uk/index.php?title=Megger
http://wiki.diyfaq.org.uk/index.php?title=Multimeter


NT

Tom wrote:

With the problem part now safely isolated and off, what equipment can
I use to locate the fault by a process of elimination? ie. removing
switches or disconnecting sections of the circuit until the bad part
is pin pointed ?

John Rumm has already given an excellent outline of the things you could do
but I'd add just one more. You know the circuit has been disconnected, but
even so, the first thing you should do is to physically check that it
really is "dead" by checking for voltage between line and earth, and
neutral and earth with your meter set for measuring voltage before
attempting to make any resistance measurements. Mistakes in identifying
cables can happen, especially if groping around in a dimly lit loft or
under floorboards. It's also good practice to check your voltmeter
beforehand by checking for voltage on a known live circuit.

--
Mike Clarke

On 19/10/10 19:18, Tom wrote:
Hi All,

Before anyone says look out, its ok the power is off for the part of
the circuit I need to test... And, naturally, I only want to test it
whilst its off.

Part of a lighting circuit has been shown (I assume) to be shorting -
a qualified electrician has disconnected the part that is causing the
problem. But they were unable to tell where the fault actually is
located.

With the problem part now safely isolated and off, what equipment can
I use to locate the fault by a process of elimination? ie. removing
switches or disconnecting sections of the circuit until the bad part
is pin pointed ?

I have a multi-volt/amp/resistance meter and I assume that would that
show me when a direct short is occurring? I suppose everything in
circuit would need to be disconnected ie. light bulbs taken out just
in case the 2 way switch is actually in the on position.

Any advice ?

Tom
there's an orange screwdriver which lights up when its near to
electricity, safer than those neon things you have to touch to wires

First I'd draw a diagram of all the switches and lights, with red and
black and blue and brown for those colours.

[g]

In message , Mike
Clarke writes
Tom wrote:

With the problem part now safely isolated and off, what equipment can
I use to locate the fault by a process of elimination? ie. removing
switches or disconnecting sections of the circuit until the bad part
is pin pointed ?

John Rumm has already given an excellent outline of the things you could do
but I'd add just one more. You know the circuit has been disconnected, but
even so, the first thing you should do is to physically check that it
really is "dead" by checking for voltage between line and earth, and
neutral and earth with your meter set for measuring voltage before
attempting to make any resistance measurements. Mistakes in identifying
cables can happen, especially if groping around in a dimly lit loft or
under floorboards. It's also good practice to check your voltmeter
beforehand by checking for voltage on a known live circuit.

Fixing nails and screws through cables have been mentioned but
incandescent lamps mounted upright can short L/N during failure.

Is the fault still there; now you have removed the lamps?

regards


--
Tim Lamb

The majority can be done by examination. With lighting, it is most likely
to be a fitting. Especially where a ceiling rose with loop in loop out has
been replaced with a fitting which doesn't offer this.
Then think of any work which has been done around the house - could a nail
etc have pierced a cable? Have switches etc been removed for decoration?

A short doesn't just develop. It has been caused in some way.

--
*If a pig loses its voice, is it disgruntled?

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Mike Clarke wrote:

t's also good practice to check your voltmeter
beforehand by checking for voltage on a known live circuit.


Call me paranoid, but I always retest a meter after it's told me that
something is indeed dead.

Dave Plowman (News) wrote:

The majority can be done by examination. With lighting, it is most likely
to be a fitting. Especially where a ceiling rose with loop in loop out has
been replaced with a fitting which doesn't offer this.
Then think of any work which has been done around the house - could a nail
etc have pierced a cable? Have switches etc been removed for decoration?

A short doesn't just develop. It has been caused in some way.

I had an 'experience' when trying to trace a fault in a lighting
circuit.
No visible damage to lamps/holders/pendants. Disconnected each, one by
one, to see if it tripped. Narrowed down to 3 lights at the far end of
the house.
Took them all apart, still couldnt find a fault. Went into loft, traced
the cables back, could still not see any damage. Had to disconnect each
in turn. Traced the line to earth fault to 3 cables behind a top hat
style steel cable covering.
Bit the bullet, and made a mess with the plasterwork, and pulled off the
covering, and the fault was plain to see, when fixing the covering, the
sparky had slightly pinched one of the cables near to a nail. It had
took 13 years since the extension was built for the wire to push through
the insulation to touch the earth - and that was the fault, the nail was
putting pressure on the cable, and had squeezed out the live cable.
Something I hadnt seen before, but has made me more aware of this when
affixing cables.
Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.

Bit the bullet, and made a mess with the plasterwork, and pulled off the
covering, and the fault was plain to see, when fixing the covering, the
sparky had slightly pinched one of the cables near to a nail. It had
took 13 years since the extension was built for the wire to push through
the insulation to touch the earth - and that was the fault, the nail was
putting pressure on the cable, and had squeezed out the live cable.
Something I hadnt seen before, but has made me more aware of this when
affixing cables.
Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.

Creep.

That's the scientific name for the process, rather than a description of the
sparky (or you!)

As you say, a useful lesson.

In article , "A.Lee" wrote:


Bit the bullet, and made a mess with the plasterwork, and pulled off the
covering, and the fault was plain to see, when fixing the covering, the
sparky had slightly pinched one of the cables near to a nail. It had
took 13 years since the extension was built for the wire to push through
the insulation to touch the earth - and that was the fault, the nail was
putting pressure on the cable, and had squeezed out the live cable.
Something I hadnt seen before, but has made me more aware of this when
affixing cables.
Alan.

I've seen that in a socket. A "professional" had left the wire ends
long, as they should be, and pushed them into the back-box when
installing faceplate. Unfortunately, the Line wire was straight out of
the terminal, bending only where it touched the metal back-box. It must
have been 10 years later when the insulation had suffered creep,
resulting in almighty bang, which took out my network... Now I see why
back boxes are earthed. I trust my DIY repair will last longer :-)

--
John W