"Earth" floating at 80-120V ... why?
Duncan Di Saudelli
I noticed that a light switch back box measured around 100V ac w.r.t. the
cold water tap in our recently-purchased house. I checked the earth bonding
on the metal pipework for the hot and the cold tap and the radiator; all are
at the same zero volt potential. I checked the earth of a nearby mains
socket and saw no p.d. between it and the pipework mentioned. I looked
around the house and I see lots of earth bonding that has been carried out
within the last 3-4 years.
Measuring a current flow to ground from this "dodgy" earth, I see a couple
of hundred microamps flowing (actually about 275uA). Not enough to hurt but
you can just about feel a "buzz" on your finger tip.
I shall start trying to trace the lighting ring main back, but I am puzzled
as to why this lighting ring earth should float when a nearby socket ring
main earth doesn't. I am yet to carry out furthr investigations i.e. other
looking at other ring circuits.
Maybe this is a simple fix but I'd appreciate some guidance before I get up
loads of floorboards etc.
thanks in advance
DDS
Harry Bloomfield
> I noticed that a light switch back box measured around 100V ac w.r.t. the
> cold water tap in our recently-purchased house. I checked the earth bonding
> on the metal pipework for the hot and the cold tap and the radiator; all are
> at the same zero volt potential. I checked the earth of a nearby mains socket
> and saw no p.d. between it and the pipework mentioned. I looked around the
> house and I see lots of earth bonding that has been carried out within the
> last 3-4 years.
You really need to make all measurements from one reference point and
that should be the consumer unit earth, so you probably need a long
cable of some sort to do that.
The sort of numbers you are quoting suggests the voltage is simply
induced from the live running adjacent to the earth. I would probably
be prudent to check the resistance of the earth from all lighting
switches and lights, to gain a better idea of what is wrong.
If the wiring dates back to the 1960's, it was not unusual for the
lighting circuits not to be provided with an earth. Later mods and
improvements to the circuits might mean metal boxes installed, but with
no earth.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
Duncan Di Saudelli
> from the live running adjacent to the earth. I would probably
D'oh! Yes, an obvious contributor. Thanks - I shall pick up on your other
points (common reference via long lead etc.) and start afresh tomorrow. I
tyake your point regarding 1960s wiring and I shall look into the earthing
of the lighting rings.
thanks for the feedback. Time for some sleep!
DDS
Dave
Another thing to consider is the sensitivity of the volt meter, The more
ohms per volt, the more you are going to get confused.
Dave
Dave Plowman (News)
Duncan Di Saudelli <n...@home.com> wrote:
> Measuring a current flow to ground from this "dodgy" earth, I see a
> couple of hundred microamps flowing (actually about 275uA). Not enough
> to hurt but you can just about feel a "buzz" on your finger tip.
> I shall start trying to trace the lighting ring main back, but I am
> puzzled as to why this lighting ring earth should float when a nearby
> socket ring main earth doesn't. I am yet to carry out furthr
> investigations i.e. other looking at other ring circuits.
For a start, lighting circuits ain't rings - they are radials.
How old is the house? Earths haven't always been required on lighting
circuits. Even although TW&E may have been used to wire them.
Most likely cause is it either isn't connected or is broken somewhere.
Especially where a ceiling rose has been replaced with an alternative
fitting which doesn't have the required terminals.
--
*Give me ambiguity or give me something else.
Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.
John Rumm
Rather than lift floorboards etc, you can do plenty of investigation
with a few simple tests first.
The lighting circuit will be a radial - with each lighting position
connecting on to the next (usually at the ceiling rose). The last one
will only have two sets of cables at the rose - one in, and one to the
switch.
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. 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.
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
Harry Bloomfield
> 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.
> 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.
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.
John Rumm
> 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.
Duncan Di Saudelli
> cold water tap in our recently-purchased house.
Thanks everyone for your advice and a few fault-finding pointers. I did
quickly realise that the voltage measured was probably sourced from a high
impedance and that measuring with a DVM with a 20M input Z would giuve
unrealistic readings - hence my decision to measure the current and see it
as only a few hundred uA i.e. a "leakage" current.
I'll start working round the ring - sorry, the radial wiring, thanks for
putting me straight - and we'll see where we get to. Hopefully I'll find a
floating "ned" which can then be tied down.
Thanks all.
DDS
John Rumm
Although more focussed on socket circuits, you may find some of this useful:
http://wiki.diyfaq.org.uk/index.php?title=Electrical_Circuit_Faults
Duncan Di Saudelli
> useful:
>
> http://wiki.diyfaq.org.uk/index.php?title=Electrical_Circuit_Faults
Definitely useful - thankyou! More reading to be done.
DDS
Dave Liquorice
> Hopefully I'll find a floating "ned" which can then be tied down.
Would need to be tied down if it was floating face down in the Clyde,
best place for it.
--
Cheers
Dave.
ARWadsworth
"John Rumm" <see.my.s...@nowhere.null> wrote in message
news:Aq2dncUlgchFfAHW...@brightview.co.uk...
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
Owain
> I got a phone call off a bloke complaining the metal backbox in the new
> 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.
If he doesn't use the proper tool for one job ...
Owain
Bob Minchin
poking boxes of any orientation.
Bob
John Rumm
But they dramatically reduce the sensitivity of your probing
equipment... ;-)
geoff
ARWadsworth <adamwa...@blueyonder.co.uk> writes
>
>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.
>
So did you ask if she did ?
--
geoff
Bill
ARWadsworth <adamwa...@blueyonder.co.uk> writes
>
>
>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 had something vaguely similar a couple of years back on my fathers
home, 200 miles away from me and in the middle of nowhere, overhead
power lines.. He was getting tingles of anything that should have been
earthed. Kitchen sink, water radiators, metal clad switches etc. It was
"interesting"
A rather fast 200 miles later........
Measuring between live and earth in the CU showed only a couple of
volts.
At the CU there was a rather old earth leakage trip, one where the earth
passed trough a separate unit to a local earth stake and any earth
current caused the trip to break the incoming supply. This had failed
and was happily still supplying the house with power.
( now replaced with something more substantial, looked like a token
gesture and probably once relied more on the lead water pipe, also new
CU with rcd now fitted )
If it had been the old days when he had a lead water pipe then it would
have either blown a fuse or warmed up the water!!
The reason for all of this was that in his green house he had trapped a
cable under a propagating frame and the VERY old rubber cable had
disintegrated inside and the live was short to the earth. There was no
separate earth to the green house it relied on the house earth via the
SWA that connected the two. The couple of volts measured at the CU were
I assume the drop in the SWA.
The moral of this is that
a) equipotential bonding works! Fine in the main house, not so sure
about the green house though with all its water and wet floors.
b) don't trust elderly, 90 year old, fathers to look after their own
electrics. c) there is a God out there looking after gardeners.
It was an interesting experience..................................
--
Bill
Dave
> Bob Minchin wrote:
>> Owain wrote:
>>> On 14 Mar, 16:29, "ARWadsworth" wrote:
>>>> 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. ...
>>>> 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.
>>>
>>> If he doesn't use the proper tool for one job ...
>>>
>>> Owain
>>>
>> I thought these days one was supposed to use insulated sleeves when
>> poking boxes of any orientation.
>
> But they dramatically reduce the sensitivity of your probing
> equipment... ;-)
Glad you wrote that, just remove any ambiguity.
Dave
Dave
ROTFL
Nice one
Dave
Gib Bogle
<snort>
Gib Bogle
> It was an interesting experience..................................
Yes. What were his power bills like?
Bill
<g.b...@auckland.no.spam.ac.nz> writes
>Bill wrote:
>
>> It was an interesting experience..................................
>
>Yes. What were his power bills like?
Strange you should ask that. I'm not sure if it was for that period but
he did have one about then that was literally about 3X normal. He had
just invested in some new lighting in the greenhouse though. The sort
seen in cannabis factories. After he got the bill he stopped using the
lighting!
I don't think his leakage problem went on long enough to make a major
impact on the bill so it probably was the lighting.
--
Bill
Gib Bogle
> In message <hnjvmq$2f9$3...@speranza.aioe.org>, Gib Bogle
> <g.b...@auckland.no.spam.ac.nz> writes
>> Bill wrote:
>>
>>> It was an interesting experience..................................
>>
>> Yes. What were his power bills like?
>
> Strange you should ask that. I'm not sure if it was for that period but
> he did have one about then that was literally about 3X normal. He had
> just invested in some new lighting in the greenhouse though. The sort
> seen in cannabis factories.
Is your dad an old hippie, by any chance?
ARWadsworth
"geoff" <ra...@kateda.org> wrote in message
news:FFGhfwBc...@demon.co.uk...
After meeting her I bet she does.
Adam
Bill
>Bill wrote:
>> In message <hnjvmq$2f9$3...@speranza.aioe.org>, Gib Bogle
>><g.b...@auckland.no.spam.ac.nz> writes
>>> Bill wrote:
>>>
>>>> It was an interesting experience..................................
>>>
>>> Yes. What were his power bills like?
>> Strange you should ask that. I'm not sure if it was for that period
>>but he did have one about then that was literally about 3X normal. He
>>had just invested in some new lighting in the greenhouse though. The
>
>Is your dad an old hippie, by any chance?
:-)
Did get me thinking though when he showed me what he was doing, actually
he hybridises fuchsias. A 45' greenhouse that can only be seen if you
are on the property and not many visitors. MMMmmmm No best
not........
--
Bill
Mike
<harry...@NOSPAM.tiscali.co.uk> wrote:
>If the wiring dates back to the 1960's, it was not unusual for the
>lighting circuits not to be provided with an earth. Later mods and
>improvements to the circuits might mean metal boxes installed, but with
>no earth.
I've seen early 60's wiring with metal backboxes for the light
switches and no earth, the wiring being double insulated either in
singles or zip connected doubles.
Makes things interesting when you contact a switchplate fixing screw
with a finger and the backbox has been made live from a missed stray
conductor (stranded not solid conductors)
--