How can I check that a neutral cable is in fact neutral? If I can measure
current then clearly is isn't neutral but measuring nothing could mean that
it isn't connected? I am fault finding my CH system and I need to confirm
whether a black wire in the junction box in the airing cupboard is neutral.

Kevin

On 03/04/2013 21:35, Kevin wrote:
How can I check that a neutral cable is in fact neutral? If I can
measure current then clearly is isn't neutral but measuring nothing
could mean that it isn't connected? I am fault finding my CH system and
I need to confirm whether a black wire in the junction box in the airing
cupboard is neutral.

Kevin

Don't panic if you see a *voltage* on it with a DVM, it's almost
certainly caused by inductive pickup from wires that it passes
alongside. If it is a voltage which can actually deliver current (check
by shorting to earth with a suitable light bulb) then you may have a
problem.

The trouble with unidentified wires around a heating system is they
might be connected to something electronic, so you don't want to zap
them with a megger (which would otherwise be a good test).

On 03/04/2013 23:20, Owain wrote:

Measure the voltage between it and a known good neutral. Should be 0V
(give or take a few mV)

And when the thermostat switches it becomes live.


--
mailto:news{at}admac(dot}myzen{dot}co{dot}uk

On Wednesday, April 3, 2013 11:54:23 PM UTC+1, alan wrote:
On 03/04/2013 23:20, Owain wrote:



Measure the voltage between it and a known good neutral. Should be 0V

(give or take a few mV)



And when the thermostat switches it becomes live.

Err, a neutral can never become live unless there's a fault somewhere.

On Thu, 4 Apr 2013 00:11:20 -0700 (PDT), Broadland Wanderer
wrote:

On Wednesday, April 3, 2013 11:54:23 PM UTC+1, alan wrote:
On 03/04/2013 23:20, Owain wrote:



Measure the voltage between it and a known good neutral. Should be 0V

(give or take a few mV)



And when the thermostat switches it becomes live.

Err, a neutral can never become live unless there's a fault somewhere.

A conductor with neutral colour insulation can quite legitimately be live (230VAC RMS).



--
Regards, Paul Herber, Sandrila Ltd.
http://www.sandrila.co.uk/ twitter: @sandrilaLtd

In article ,
Broadland Wanderer wrote:
On Wednesday, April 3, 2013 11:54:23 PM UTC+1, alan wrote:
On 03/04/2013 23:20, Owain wrote:



Measure the voltage between it and a known good neutral. Should be 0V

(give or take a few mV)



And when the thermostat switches it becomes live.

Err, a neutral can never become live unless there's a fault somewhere.

What he means is that the wire he's identifies as neutral becomes the same
potential as the live when the theromstat closes. The fault is that the
wire is not connected to the neutral of the circuit.

--
From KT24

Using a RISC OS computer running v5.18

On Thursday, April 4, 2013 8:20:37 AM UTC+1, Paul Herber wrote:
On Thu, 4 Apr 2013 00:11:20 -0700 (PDT), Broadland Wanderer

wrote:



On Wednesday, April 3, 2013 11:54:23 PM UTC+1, alan wrote:

On 03/04/2013 23:20, Owain wrote:







Measure the voltage between it and a known good neutral. Should be 0V



(give or take a few mV)







And when the thermostat switches it becomes live.



Err, a neutral can never become live unless there's a fault somewhere.



A conductor with neutral colour insulation can quite legitimately be live (230VAC RMS).

I didn't say it couldn't. I said a neutral can never become live unless there's a fault.

In article ,
Broadland Wanderer wrote:
On Thursday, April 4, 2013 8:20:37 AM UTC+1, Paul Herber wrote:
On Thu, 4 Apr 2013 00:11:20 -0700 (PDT), Broadland Wanderer

wrote:



On Wednesday, April 3, 2013 11:54:23 PM UTC+1, alan wrote:

On 03/04/2013 23:20, Owain wrote:







Measure the voltage between it and a known good neutral. Should be
0V



(give or take a few mV)







And when the thermostat switches it becomes live.



Err, a neutral can never become live unless there's a fault somewhere.



A conductor with neutral colour insulation can quite legitimately be
live (230VAC RMS).

I didn't say it couldn't. I said a neutral can never become live unless
there's a fault.


but even that isn't necessarily true. The neutral wire might have been
deliberately disconnected to help with circuit tracing.

--
From KT24

Using a RISC OS computer running v5.18

"Kevin" wrote:
How can I check that a neutral cable is in fact neutral? If I can measure
current then clearly is isn't neutral but measuring nothing could mean
that it isn't connected? I am fault finding my CH system and I need to
confirm whether a black wire in the junction box in the airing cupboard is neutral.

Kevin

There should be the same current in the Neutral as the Live, if not there
is a fault. That is a basic law of electronics.

I suspect you mean Voltage.

The neutral may not be at zero volts for a number of reasons, including
faults.

Do you know if your house has a PME Earth? ( there should be a notice by
the meter). If it has, with the power off, compare the resistance between a
pipe and the neutral with a pipe and the earth. The cable runs should be
the same so the resistance should be the same.

On 03/04/2013 21:35, Kevin wrote:
How can I check that a neutral cable is in fact neutral? If I can
measure current then clearly is isn't neutral but measuring nothing
could mean that it isn't connected? I am fault finding my CH system and
I need to confirm whether a black wire in the junction box in the airing
cupboard is neutral.

Kevin

I think you'll see from the range of answers given that it ain't easy!
It's not too difficult to establish that a wire is connected *either* to
the supply's neutral *or* to earth, but distinguishing one from the
other is harder.

Can you not find the other end of said cable, and see what it's
connected to. That's probably the best way.

If you've got a sensitive AC voltmeter, you may get a clue by measuring
the voltage between your wire and a known good earth. Start by measuring
the earth to neutral voltage in a nearby 13A socket. [In my case, it's
about 130mV - but this will depend on your installation]. Then measure
the voltage between your mystery wire and this same earth point. If
it's the same as you measured before, it's probably a neutral. If it's
zero, it's probably an earth.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On Thursday, April 4, 2013 9:54:23 AM UTC+1, charles wrote:
In article ,

Broadland Wanderer wrote:









I didn't say it couldn't. I said a neutral can never become live unless

there's a fault.





but even that isn't necessarily true. The neutral wire might have been

deliberately disconnected to help with circuit tracing.

I rather think you're splitting hairs.

If one is fault locating or tracing circuits, it's not unreasonable to assume that the person carrying out the work has a proper level of competency, and will be fully aware that this may be the case. If not they shouldn't be carrying out this type of work.

I have my suspicions about the competency of the OP, talking about measuring current when it was fairly obvious he meant voltage.

On 04/04/2013 10:11, Brian Reay wrote:
"Kevin" wrote:
How can I check that a neutral cable is in fact neutral? If I can measure
current then clearly is isn't neutral but measuring nothing could mean
that it isn't connected? I am fault finding my CH system and I need to
confirm whether a black wire in the junction box in the airing cupboard is neutral.

Kevin

There should be the same current in the Neutral as the Live, if not there
is a fault. That is a basic law of electronics.

I suspect you mean Voltage.

The neutral may not be at zero volts for a number of reasons, including
faults.

Do you know if your house has a PME Earth? ( there should be a notice by
the meter). If it has, with the power off, compare the resistance between a
pipe and the neutral with a pipe and the earth. The cable runs should be
the same so the resistance should be the same.

I'm guessing from the question that the OP will have, at best, a
multimeter and not more professional test kit. So he won't be able to
measure normal circuit resistance. In any case you don't know what the
cable runs might be, nor can you be sure if there is electrical
continuity in the pipework, or where it might be bonded to earth.

The question about PME is good, though (provided OP knows what PME is).

With the power off, he could test for continuity with a known neutral,
e.g. at a socket. If there is continuity, it probably is a neutral. If
it is a switched live, e.g. from a thermostat, it would (probably) not
be connected to the known neutral. Where a switched live is connected to
a terminal it should really have red sleeve on it, or at least a bit of
red tape as a warning.

There are wiring diagrams for CH junction boxes on the web; sorry I
don't have any links but try Honeywell for a start.

--
For every complex problem, there is a solution which is simple, neat,
and wrong.
H L Menken

On Thursday, April 4, 2013 9:57:36 AM UTC+1, wrote:
On 4 Apr,

Broadland Wanderer wrote:



Err, a neutral can never become live unless there's a fault somewhere.



A neutral is by definition a live conductor. It /may/ (should) be near earth

potential normally unless there is a fault.


I rather think that's what I said.


It is not unusual to have the neutral switched (by a thermostat or such)

inside equipment, but it should never be single pole switched in fixed

wiring.

I am well aware that the neutral may be switched within equipment, but that's something of a red herring. The OP mentioned a junction box in his airing cupboard.

On 04/04/2013 10:51, Roger Mills wrote:
On 03/04/2013 21:35, Kevin wrote:
How can I check that a neutral cable is in fact neutral? If I can
measure current then clearly is isn't neutral but measuring nothing
could mean that it isn't connected? I am fault finding my CH system and
I need to confirm whether a black wire in the junction box in the airing
cupboard is neutral.

Kevin

I think you'll see from the range of answers given that it ain't easy!
It's not too difficult to establish that a wire is connected *either* to
the supply's neutral *or* to earth, but distinguishing one from the
other is harder.


Note also that the *real* experts on this NG are studiously avoiding
posting.
It *could* be a can of worms. Personally, I think it is worth trying to
help
people in trouble even if we worry that they may not be fully competent.
Perhaps
all these posts should carry a "health warning": anything you do is at
your own
risk if you don't know the "basics". Also you may have missed out
essential information.

On Friday, April 5, 2013 3:09:48 PM UTC+1, newshound wrote:

Note also that the *real* experts on this NG are studiously avoiding

posting.

It *could* be a can of worms.

It's not difficult to prove if a cable is a circuit neutral at a junction box, but that also requires one to prove that it's not a de-energised switch wire. It's not quite so easy to prove that without knowing exactly how the wiring has been configured.

Personally, I think it is worth trying to

help

people in trouble even if we worry that they may not be fully competent.

We must agree to disagree on that topic. Interestingly, the OP has made no further comment since his original.

Determining a neutral or a de-energised switch wire requires two very simple proving tests before and after the event, ideally using a test lamp[1], but a multimeter will work just as well.

[1] I favour the test lamp, it indicates - or doesn't - immediately in your field of view, whilst one is concentrating on where the prods are directed.. A meter has its uses, but usually requires a bit of manual dexterity/juggling and eye movement between prods and a decent view of the readout. Cheap digital meters are also prone to spurious readings, much less so with quality test equipment.

newshound wrote:
On 04/04/2013 10:51, Roger Mills wrote:
On 03/04/2013 21:35, Kevin wrote:
How can I check that a neutral cable is in fact neutral? If I can
measure current then clearly is isn't neutral but measuring
nothing could mean that it isn't connected? I am fault finding my
CH system and I need to confirm whether a black wire in the
junction box in the airing cupboard is neutral.

Kevin

I think you'll see from the range of answers given that it ain't
easy! It's not too difficult to establish that a wire is connected
*either* to the supply's neutral *or* to earth, but distinguishing
one from the other is harder.


Note also that the *real* experts on this NG are studiously avoiding
posting.
It *could* be a can of worms. Personally, I think it is worth trying
to help
people in trouble even if we worry that they may not be fully
competent. Perhaps
all these posts should carry a "health warning": anything you do is at
your own
risk if you don't know the "basics". Also you may have missed out
essential information.

I cannot think of a standard wiring CH setup that does not have a neutral in
the wiring centre (all motorised zone valves need a neutral).

Standard set ups are here

http://wiki.diyfaq.org.uk/index.php?...s_and_Zonin g

If the OP gives a little more detail - including the problems with the CH,
maybe a photo and also says what setup he has we could get an answer to his
problems.

I was not avoiding the post - it's the sort of post I enjoy. My first
thought was that the OP is assuming that a black cable is a neutral (as
pointed out by others).


--
Adam

On 05/04/2013 18:57, ARW wrote:
newshound wrote:
On 04/04/2013 10:51, Roger Mills wrote:
On 03/04/2013 21:35, Kevin wrote:
How can I check that a neutral cable is in fact neutral? If I can
measure current then clearly is isn't neutral but measuring
nothing could mean that it isn't connected? I am fault finding my
CH system and I need to confirm whether a black wire in the
junction box in the airing cupboard is neutral.

Kevin

I think you'll see from the range of answers given that it ain't
easy! It's not too difficult to establish that a wire is connected
*either* to the supply's neutral *or* to earth, but distinguishing
one from the other is harder.


Note also that the *real* experts on this NG are studiously avoiding
posting.
It *could* be a can of worms. Personally, I think it is worth trying
to help
people in trouble even if we worry that they may not be fully
competent. Perhaps
all these posts should carry a "health warning": anything you do is at
your own
risk if you don't know the "basics". Also you may have missed out
essential information.

I cannot think of a standard wiring CH setup that does not have a neutral in
the wiring centre (all motorised zone valves need a neutral).

Standard set ups are here

http://wiki.diyfaq.org.uk/index.php?...s_and_Zonin g

If the OP gives a little more detail - including the problems with the CH,
maybe a photo and also says what setup he has we could get an answer to his
problems.

I was not avoiding the post - it's the sort of post I enjoy. My first
thought was that the OP is assuming that a black cable is a neutral (as
pointed out by others).



IIRC, he had a working system, took it apart to tidy up the wiring, or
whatever, thought he knew what was what but found it didn't work when
re-assembled. So he's now trying to figure out which wire is for which
function!

I think it's the same person who was asking about S-Plan wiring. Various
people pointed him at the schematics, and I gave him a verbal
description of how it is supposed to work.

If he can't sort it out from that, he needs to employ someone who can!

As we all know, the electrics for many (most?) CH systems have been
installed by non-electricians, using whatever wire was to hand - so you
can deduce very little from the colour of a conductor.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
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