Searching \ for '[EE]: Checking home wiring with a multimeter' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=checking+home+wiring
Search entire site for: 'Checking home wiring with a multimeter'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: Checking home wiring with a multimeter'
2006\01\03@140058 by Lindy Mayfield

flavicon
face
I was installing ceiling lights in the new house and wanted to be "smart" and double check to see if the exposed wires were hot or not.  So I connected my multimeter first just in case.  I grew up in the US so I am not very familiar with connecting things here in Europe and I wanted to be careful.  

I was a little surprised when my meter showed first around 118 or so volts AC and then when the switch was flipped it jumped up to about 230.  This kind of made me nervous, so of course I made the shorts test with what I thought was the off position before proceeding.  (The shorts test is when I touch the wires together and then check my shorts for signs of electrocution.)

Needless to say I survived, but I was wondering why I was getting a ~120 volt reading when the light switch was off?

Thanks,
Lindy


2006\01\03@152835 by Dominic Stratten

picon face
part 1 1604 bytes content-type:text/plain; (decoded 7bit)

Mains wiring picking up stray inductive currents ?

I had a similar one when I moved into my new house - there was a wire
sticking up out of the floor with bare wires at the end - I tested with a
meter and it showed 127v AC although in the UK we are on 220-240v.

I did the brave thing and shorted the wires together - nothing happened, no
fuses blew and I'm still here (and its still buried under concrete 10 years
later with no ill effects).

One of those wonderful mysteries in house wiring :-P

{Original Message removed}

2006\01\03@153004 by Bob J

picon face
Meters are generally not good to use on household circuits, the long runs of
wire act as capacitors.  Even the no-contact pen-type testers will indicate
a circuit is live when it really isn't.  The best way to check household
wiring is with a cheap electrical testing light.

Regards,
Bob

On 1/3/06, Lindy Mayfield <spam_OUTLindy.MayfieldTakeThisOuTspamssf.sas.com> wrote:
{Quote hidden}

> -

2006\01\03@154802 by Gerhard Fiedler

picon face
Lindy Mayfield wrote:

> I was installing ceiling lights in the new house and wanted to be "smart"
> and double check to see if the exposed wires were hot or not.  So I
> connected my multimeter first just in case.  I grew up in the US so I am
> not very familiar with connecting things here in Europe and I wanted to
> be careful.
>
> I was a little surprised when my meter showed first around 118 or so
> volts AC and then when the switch was flipped it jumped up to about 230.
>  This kind of made me nervous, so of course I made the shorts test with
> what I thought was the off position before proceeding.  (The shorts test
> is when I touch the wires together and then check my shorts for signs of
> electrocution.)
>
> Needless to say I survived, but I was wondering why I was getting a ~120
> volt reading when the light switch was off?

Could that be induction? BTW, I'm not that familiar with international
wiring and voltage standards, but I'm pretty sure you can't speak of
"European" home wiring; every country has its own standards.

Gerhard

2006\01\03@154938 by Howard Winter

face
flavicon
picon face
Lindy,

On Tue, 3 Jan 2006 21:00:56 +0200, Lindy Mayfield wrote:

> I was installing ceiling lights in the new house and wanted to be "smart" and double check to see if the
exposed wires were hot or not.  So I connected my multimeter first just in case.  I grew up in the US so I am
not very familiar with connecting things here in Europe and I wanted to be careful.  
>
> I was a little surprised when my meter showed first around 118 or so volts AC and then when the switch was
flipped it jumped up to about 230.

Where were measuring, across the Live/Neutral, or Live/Earth?

> This kind of made me nervous, so of course I made the shorts test with what I thought was the off position
before proceeding.  (The shorts test is when I touch the wires together and then check my shorts for signs of
electrocution.)

LOL!

> Needless to say I survived, but I was wondering why I was getting a ~120 volt reading when the light switch
was off?

First it could be wired as switched neutral - I've found a number of houses in England like this - very dodgy
because across the wires reads dead, but one side is live.  This is something that catches you out once only!  
:-)

Secondly a multimeter has a very high impedance, so you may be measuring the voltage induced by the wiring.  
The only safe way to work on a circuit is with it isolated - at the distribution board, not just at the
switch.

Cheers,


Howard Winter
St.Albans, England


2006\01\03@155606 by Roy

flavicon
face
part 1 1966 bytes content-type:text/plain; (decoded 7bit)

Modern digital and some analog meters have high impedance inputs that do
not load the circuit under test and therefore can show a reading from
inductive pickup from cables running beside the one under test.

That is why electricians use the two prong tester that has a neon light
inside it and a vibration unit that gives the circuit some load.

I am not sure about Europe but the "international colour code"

Brown for live phase 230v or 115v
Blue for neutral (In NZ the neutral is tied to earth at the
switchboard).
Green with yellow strip for earth.



> {Original Message removed}
part 2 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2006\01\03@160656 by Danny Sauer

flavicon
face
Roy wrote regarding 'RE: [EE]: Checking home wiring with a multimeter' on Tue, Jan 03 at 14:58:
> I am not sure about Europe but the "international colour code"
>
> Brown for live phase 230v or 115v
> Blue for neutral (In NZ the neutral is tied to earth at the
> switchboard).
> Green with yellow strip for earth.

How come my US electrical box is full of red (-110 relative to
neutral), black (+110v relative to neutral), and white or green
(neutral) wires?  :)

--Danny

2006\01\03@161554 by Mike Hagen

flavicon
face
These are the standard colors for line cords with only one phase present.
It became a standard
on all the medical stuff I worked on here in the US.  I used to practice
saying to myself "Brown is BLACK!"  I don't know what they would use for
another leg?

{Original Message removed}

2006\01\03@162529 by Herbert Graf

flavicon
face
On Wed, 2006-01-04 at 09:56 +1300, Roy wrote:
> Modern digital and some analog meters have high impedance inputs that do
> not load the circuit under test and therefore can show a reading from
> inductive pickup from cables running beside the one under test.
>
> That is why electricians use the two prong tester that has a neon light
> inside it and a vibration unit that gives the circuit some load.
>
> I am not sure about Europe but the "international colour code"
>
> Brown for live phase 230v or 115v
> Blue for neutral (In NZ the neutral is tied to earth at the
> switchboard).
> Green with yellow strip for earth.

International, except of course for most of North America where much of
our wiring is:

Hot: black
Neutral: white
Ground: green or bare copper
2nd hot: red

TTYL

-----------------------------
Herbert's PIC Stuff:
http://repatch.dyndns.org:8383/pic_stuff/

2006\01\03@164300 by Danny Sauer

flavicon
face
Mike wrote regarding 'Re: [EE]: Checking home wiring with a multimeter' on Tue, Jan 03 at 15:18:
> These are the standard colors for line cords with only one phase present.
> It became a standard
> on all the medical stuff I worked on here in the US.  I used to practice
> saying to myself "Brown is BLACK!"  I don't know what they would use for
> another leg?

Now that you mention ig, I've seen some equipment roll through with
blue and black wires inside (most recent was a large UPS), but just
chalked it up to some manufacturer getting a deal on a spool of wire
in that color or something.  Here, they were following standards all
along.  Weird. :)

--Danny

2006\01\03@171316 by Howard Winter

face
flavicon
picon face
Danny,

On Tue, 3 Jan 2006 15:06:56 -0600, Danny Sauer wrote:

{Quote hidden}

That's easy - the US isn't "International" !  :-)

Cheers,


Howard Winter
St.Albans, England


2006\01\03@172353 by Howard Winter

face
flavicon
picon face
Roy,

On Wed, 4 Jan 2006 09:56:03 +1300, Roy wrote:

>...
> I am not sure about Europe but the "international colour code"
>
> Brown for live phase 230v or 115v
> Blue for neutral (In NZ the neutral is tied to earth at the
> switchboard).
> Green with yellow strip for earth.

I don't know how international this is - these "harmonised" colours (and the others used for 3-phase wiring)
haven't been agreed for very long, and most in-place wiring will follow old national standards (at least one
of which used red for Earth!).

In the UK the Brown / Blue / Green-Yellow has been used for portable wiring (flex) for some time, but for
installed wiring our old standard of Red / Black / Green-Yellow has only been superceded recently - it could
still be used up to the beginning of this year, I believe.

So although in theory there is an international standard, the colours you will actually find will vary a lot
from one country to another - as will the wiring standards and techniques.  For example, in the UK nowadays
lighting is often wired using the "loop-in" system, which means that every ceiling rose will have live wires
at all times, which is why I don't recommend wiring changes with the power to that circuit turned on!

Cheers,


Howard Winter
St.Albans, England


2006\01\04@191535 by Peter

picon face


On Tue, 3 Jan 2006, Lindy Mayfield wrote:

{Quote hidden}

You would have gotten 0 with the lightbulb in. The floating wire in the
wall (when the switch is off) gets phase ac coupled into it and at the
same time leaks (ac) to ground. So you can see a voltage that's about
half of the mains on almost any floating wire in a conduit that also
carries a phase.

This is one of the reasons why it is totally forbidden to put signal
cables into power conduits.

Peter

More... (looser matching)
- Last day of these posts
- In 2006 , 2007 only
- Today
- New search...