Hi All,

I have some 12v spotlights in my bathroom. I needed to move one so disconnected it some time ago and have eventually cut the new hole today. Having now forgotten which way it was wired I thought I should check with a multi meter to be on the safe side. It is 3 core and earth and the results (all AC) are as follows

With switch off
Grey - brown 146v
Grey - black 240v
Brown - black 76v

With switch on
Grey - brown 240v
Grey - black 240v
Brown - black 0v

So for this I conclude that
Grey is neutral
black is perm live
Brown is switched live

Is this correct ? More worryingly any idea why I am getting spurious voltages when the switch is off?

Thanks in advance

Lee.

On Saturday, 9 November 2019 16:46:37 UTC, Lee Nowell wrote:
So for this I conclude that
Grey is neutral
black is perm live
Brown is switched live

Is this correct ?

Probably. But it's certainly not 12 volts :-)

More worryingly any idea why I am getting spurious voltages when the switch
is off?

Induced voltage from parallel conductors.

With cables having coupling in the order of about 100pf/metre (minimum), it only takes 10m to get a whole 1nF (i.e. 73uA leakage). Digital multimeters (good ones, that is) are about 20Mohm input. If you measure with a good ol' analogue meter you'll probably find a lot lower than [76V].

https://www2.theiet.org/forums/forum...&threadid=3053

See also

https://diy.stackexchange.com/questi...-be-at-0-volts

Owain

On 09/11/2019 17:09, wrote:
On Saturday, 9 November 2019 16:46:37 UTC, Lee Nowell wrote:
So for this I conclude that
Grey is neutral
black is perm live
Brown is switched live

Is this correct ?

Probably. But it's certainly not 12 volts :-)

More worryingly any idea why I am getting spurious voltages when the switch
is off?

Induced voltage from parallel conductors.

With cables having coupling in the order of about 100pf/metre (minimum), it only takes 10m to get a whole 1nF (i.e. 73uA leakage). Digital multimeters (good ones, that is) are about 20Mohm input. If you measure with a good ol' analogue meter you'll probably find a lot lower than [76V].

https://www2.theiet.org/forums/forum...&threadid=3053

See also

https://diy.stackexchange.com/questi...-be-at-0-volts

+1


--
Adam

On Saturday, 9 November 2019 16:46:37 UTC, Lee Nowell wrote:
Hi All,

I have some 12v spotlights in my bathroom. I needed to move one so disconnected it some time ago and have eventually cut the new hole today. Having now forgotten which way it was wired I thought I should check with a multi meter to be on the safe side. It is 3 core and earth and the results (all AC) are as follows

With switch off
Grey - brown 146v
Grey - black 240v
Brown - black 76v

With switch on
Grey - brown 240v
Grey - black 240v
Brown - black 0v

So for this I conclude that
Grey is neutral
black is perm live
Brown is switched live

Is this correct ? More worryingly any idea why I am getting spurious voltages when the switch is off?

Thanks in advance

Lee.

Looks right. Cable capacitance plus a modern high impedance meter - use an old lower R one and those stray Vs will fall away. No earth conductor though?


NT

The meter is an old (circa 30 years) fluke meter. Good quality but old. There is earth at the junction box - should I run some more reading with that?

On 09/11/2019 19:21, Lee Nowell wrote:
The meter is an old (circa 30 years) fluke meter. Good quality but old. There is earth at the junction box - should I run some more reading with that?

A 30-year old digital meter will probably be 20M or more, while an
older, analogue meter might be 10K.

SteveW

On 09/11/2019 19:21, Lee Nowell wrote:
The meter is an old (circa 30 years) fluke meter. Good quality but
old. There is earth at the junction box - should I run some more
reading with that?

Some Fluke's like a few of the 100 series have a special low impedance
range designed to combat this kind of phantom reading. When selected the
input impedance drops to around 3K.




--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Saturday, 9 November 2019 20:51:03 UTC, Steve Walker wrote:
On 09/11/2019 19:21, Lee Nowell wrote:

The meter is an old (circa 30 years) fluke meter. Good quality but old. There is earth at the junction box - should I run some more reading with that?

A 30-year old digital meter will probably be 20M or more, while an
older, analogue meter might be 10K.

SteveW

Decent moving pointers were 50k/volt, so 15M on a 300v dc scale, half that on ac. Rock bottom ones were 1k/v so 150k for 300v ac scale.


NT

On 10/11/2019 03:43, wrote:
On Saturday, 9 November 2019 20:51:03 UTC, Steve Walker wrote:
On 09/11/2019 19:21, Lee Nowell wrote:

The meter is an old (circa 30 years) fluke meter. Good quality but old. There is earth at the junction box - should I run some more reading with that?

A 30-year old digital meter will probably be 20M or more, while an
older, analogue meter might be 10K.

SteveW

Decent moving pointers were 50k/volt, so 15M on a 300v dc scale, half that on ac. Rock bottom ones were 1k/v so 150k for 300v ac scale.



Well I never knew before that the Avo 8 (with 1000 ohms-per-volt on AC
ranges of 100V and upwards) was at least close to "rock bottom" in the
moving coil meter market.


--
Robin
reply-to address is (intended to be) valid

On Saturday, 9 November 2019 16:46:37 UTC, Lee Nowell wrote:
Hi All,

I have some 12v spotlights in my bathroom. I needed to move one so disconnected it some time ago and have eventually cut the new hole today. Having now forgotten which way it was wired I thought I should check with a multi meter to be on the safe side. It is 3 core and earth and the results (all AC) are as follows

With switch off
Grey - brown 146v
Grey - black 240v
Brown - black 76v

With switch on
Grey - brown 240v
Grey - black 240v
Brown - black 0v

So for this I conclude that
Grey is neutral
black is perm live
Brown is switched live

Is this correct ? More worryingly any idea why I am getting spurious voltages when the switch is off?

Thanks in advance

Lee.

If your meter is one of these cheap"mickey mouse" ones. they often give spurious readings. It's on account of the tiny current they draw.

On Sun, 10 Nov 2019 07:06:54 +0000, Robin wrote:

On 10/11/2019 03:43, wrote:
On Saturday, 9 November 2019 20:51:03 UTC, Steve Walker wrote:
On 09/11/2019 19:21, Lee Nowell wrote:

The meter is an old (circa 30 years) fluke meter. Good quality but
old. There is earth at the junction box - should I run some more
reading with that?

A 30-year old digital meter will probably be 20M or more, while an
older, analogue meter might be 10K.

SteveW

Decent moving pointers were 50k/volt, so 15M on a 300v dc scale, half
that on ac. Rock bottom ones were 1k/v so 150k for 300v ac scale.



Well I never knew before that the Avo 8 (with 1000 ohms-per-volt on AC
ranges of 100V and upwards) was at least close to "rock bottom" in the
moving coil meter market.

Generally was lower on AC ranges. For DC, was 20,000 ohms-per-volt.

I have one of the last ones manufactured.

--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

On Sat, 9 Nov 2019 20:50:58 +0000, Steve Walker wrote:

On 09/11/2019 19:21, Lee Nowell wrote:
The meter is an old (circa 30 years) fluke meter. Good quality but old. There is earth at the junction box - should I run some more reading with that?

A 30-year old digital meter will probably be 20M or more, while an
older, analogue meter might be 10K.

SteveW

Had tis on a complex circuit: seemed to be from an octal relay, but only
about 230V on a DMM.
AVO 8 showed about 200-odd, dropped the range and the figure went down, got
to lowest range and bit above FA there.
Slightly bent fixed contact, little tweak and it was OK.
--
Peter.
The gods will stay away
whilst religions hold sway

On 10/11/2019 08:29, Bob Eager wrote:
On Sun, 10 Nov 2019 07:06:54 +0000, Robin wrote:

On 10/11/2019 03:43, wrote:
On Saturday, 9 November 2019 20:51:03 UTC, Steve Walker wrote:
On 09/11/2019 19:21, Lee Nowell wrote:

The meter is an old (circa 30 years) fluke meter. Good quality but
old. There is earth at the junction box - should I run some more
reading with that?

A 30-year old digital meter will probably be 20M or more, while an
older, analogue meter might be 10K.

SteveW

Decent moving pointers were 50k/volt, so 15M on a 300v dc scale, half
that on ac. Rock bottom ones were 1k/v so 150k for 300v ac scale.



Well I never knew before that the Avo 8 (with 1000 ohms-per-volt on AC
ranges of 100V and upwards) was at least close to "rock bottom" in the
moving coil meter market.

Generally was lower on AC ranges. For DC, was 20,000 ohms-per-volt.

Indeed - which is still far short of "decent" (as defined above).

I have one of the last ones manufactured.

Mine was made in the 60s - and the leads are rather inflexible as a
result of the copious tape where the insulation has perished. (Me too
mean to buy new leads for what is very, very occasional use.)

--
Robin
reply-to address is (intended to be) valid

Yes I'm assuming each light has its own transformer and the wiring is thus
at mains volts. Not sure about the odd colours though.
What one needs is a tungsten lamp on a bit of wire. Beats a meter for this
stuff any day! grin.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
wrote in message
...
On Saturday, 9 November 2019 16:46:37 UTC, Lee Nowell wrote:
So for this I conclude that
Grey is neutral
black is perm live
Brown is switched live

Is this correct ?

Probably. But it's certainly not 12 volts :-)

More worryingly any idea why I am getting spurious voltages when the
switch
is off?

Induced voltage from parallel conductors.

With cables having coupling in the order of about 100pf/metre (minimum), it
only takes 10m to get a whole 1nF (i.e. 73uA leakage). Digital multimeters
(good ones, that is) are about 20Mohm input. If you measure with a good ol'
analogue meter you'll probably find a lot lower than [76V].

https://www2.theiet.org/forums/forum...&threadid=3053

See also

https://diy.stackexchange.com/questi...-be-at-0-volts

Owain

Brian Gaff wrote:

Not sure about the odd colours

grey, black and brown is the new blue, yellow and red for three core cable.

I used to have an old TMK analogue meter that had a button that actually put
a fairly large wattage resistor across the probes so you could see what
actually happened under a minimal load, and it used to be very surprising on
even fairly short runs of wire at 240v ac.

Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Steve Walker" wrote in message
...
On 09/11/2019 19:21, Lee Nowell wrote:
The meter is an old (circa 30 years) fluke meter. Good quality but old.
There is earth at the junction box - should I run some more reading with
that?

A 30-year old digital meter will probably be 20M or more, while an older,
analogue meter might be 10K.

SteveW

On Sunday, 10 November 2019 07:06:58 UTC, Robin wrote:
On 10/11/2019 03:43, tabbypurr wrote:
On Saturday, 9 November 2019 20:51:03 UTC, Steve Walker wrote:
On 09/11/2019 19:21, Lee Nowell wrote:

The meter is an old (circa 30 years) fluke meter. Good quality but old. There is earth at the junction box - should I run some more reading with that?

A 30-year old digital meter will probably be 20M or more, while an
older, analogue meter might be 10K.

SteveW

Decent moving pointers were 50k/volt, so 15M on a 300v dc scale, half that on ac. Rock bottom ones were 1k/v so 150k for 300v ac scale.



Well I never knew before that the Avo 8 (with 1000 ohms-per-volt on AC
ranges of 100V and upwards) was at least close to "rock bottom" in the
moving coil meter market.

The Avo 8 is something from the 1930s. A lot changed since then thankfully. 1k/volt is precisely what rock bottom analog meters from the 60s on were. Rock bottom in the 1930s was the watch type moving iron meters, much less than 1k/volt.


NT

On 10/11/2019 07:43, harry wrote:

If your meter is one of these cheap "mickey mouse" ones. they often
give spurious readings.

That's not even wrong...

With analogue meters, the better the quality, typically the higher the
input impedance. This is in the majority of measurement circumstances a
desirable characteristic since it reduces the parasitic effect of the
meter on the circuit under test.

With digital meters the input impedances are typically significantly
higher. Again in many cases this is a "good thing", although it is a
trap for the unwary with "floating" circuit cables in close proximity to
mains voltages.

It's on account of the tiny current they draw.

An ideal meter would draw no current at all when measuring voltage.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article ,
wrote:
On Sunday, 10 November 2019 07:06:58 UTC, Robin wrote:
On 10/11/2019 03:43, tabbypurr wrote:
On Saturday, 9 November 2019 20:51:03 UTC, Steve Walker wrote:
On 09/11/2019 19:21, Lee Nowell wrote:

The meter is an old (circa 30 years) fluke meter. Good quality but
old. There is earth at the junction box - should I run some more
reading with that?

A 30-year old digital meter will probably be 20M or more, while an
older, analogue meter might be 10K.

SteveW

Decent moving pointers were 50k/volt, so 15M on a 300v dc scale, half
that on ac. Rock bottom ones were 1k/v so 150k for 300v ac scale.



Well I never knew before that the Avo 8 (with 1000 ohms-per-volt on AC
ranges of 100V and upwards) was at least close to "rock bottom" in the
moving coil meter market.

The Avo 8 is something from the 1930s.

The AVO 8 came out in 1951 and stayed in production until 2008

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

In article 07c01b02-2b0f-4c66-9f1d-
, says...

On Sunday, 10 November 2019 07:06:58 UTC, Robin wrote:
On 10/11/2019 03:43, tabbypurr wrote:

Well I never knew before that the Avo 8 (with 1000 ohms-per-volt on AC
ranges of 100V and upwards) was at least close to "rock bottom" in the
moving coil meter market.

The Avo 8 is something from the 1930s. A lot changed since then thankfully. 1k/volt is precisely what rock bottom analog meters from the 60s on were. Rock bottom in the 1930s was the watch type moving iron meters, much less than 1k/volt.


When I started work in a TV service department in 1960, all
the meters were AVO 8 models. All service data quoted 'all
readings taken with 20k/volt meter', which is what the AVO 8
was.

However, looking at info for sets we were still repairing, the
voltages had obviously been taklen using its predecessor, the
AVO 7.

This points to the AVO 8 being introduced around the mid 50s

The above relates only to the DC ranges, of course.

The AVO 8 was regarded as the top of the range and had a price
tag to match - certainly well out of my league.

My first meter had a similar specification but not the
mechanical robustness, nor the 'bombproof' cut-out protected
movement of the AVO but it served its purpose well. I may
still have it around somewhere.

--

Terry