stray earth voltage


Postby gavski » Thu Jan 12, 2012 4:52 pm

I have removed a 3 way hanging chord from my bedroom, during removal I noticed a 9 volt earth leak in the junction box in the loft.

I noticed this because I had to remove the earth from a splicing block. When I touched the earth and another, I got a tingle, I tested it with a fluke and got a 9v reading between the 2 earth wires.?
any ideas?

thanks
gavski
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Joined: Sat Oct 02, 2010 1:46 pm

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Postby sparx » Thu Jan 12, 2012 9:59 pm

Hi,
somewhere on the circuit a light, maybe a fluorescent or low voltage transformer in light or possible shaver transformer has some leakage, not unusual.
By disconnecting the circuit earth (cpc) you allow it to 'float' up to some value, RECONNECT IT straight away please!
If you are interested and feel confident try using a wander lead from another earthed point through your test meter to the reconnected earths at the JB and confirm no voltage showing.
One way would be by connecting to the earth pin only in a spare 13A plug and testing from a socket.
Take care, 50 Volts will cause more than 30mA through the average human body which is considered the max safe current!
sparx
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Joined: Wed Mar 21, 2007 8:33 pm
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Postby gavski » Sat Jan 14, 2012 3:03 pm

sparx wrote:Hi,
somewhere on the circuit a light, maybe a fluorescent or low voltage transformer in light or possible shaver transformer has some leakage, not unusual.
By disconnecting the circuit earth (cpc) you allow it to 'float' up to some value, RECONNECT IT straight away please!
If you are interested and feel confident try using a wander lead from another earthed point through your test meter to the reconnected earths at the JB and confirm no voltage showing.
One way would be by connecting to the earth pin only in a spare 13A plug and testing from a socket.
Take care, 50 Volts will cause more than 30mA through the average human body which is considered the max safe current!

Thanks for your reply sparx.
I re-connected the earth and the voltage has returned to zero, I tested from other earths (including water pipes etc) to the earths in the JB - no voltage. Am I to assume all is ok? I'm happy as long as there is not an inherent problem in the lighting circut that may become a problem in the future?
thanks
gavski
Posts: 21
Joined: Sat Oct 02, 2010 1:46 pm


Postby sparx » Sun Jan 15, 2012 12:26 pm

Hi Gavski,
Yes as the earth wire is doing its primary job of keeping exposed metal work at or near earth potential ie 0v.
Even if no actual leakage is there the fact that the Circuit Protective Conductor (earth wire) runs alongside the live ones means if it is disconnected from earth then as its AC, transformer type linking and capacitive coupling takes place which will induce a voltage in the earth.
Capacitor: alternate layers of conductor/insulator/conductor.
regards Sparx
sparx
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Joined: Wed Mar 21, 2007 8:33 pm
Location: The fifth continent.


Postby gavski » Mon Jan 16, 2012 10:48 am

Thanks again you've been a big help and I've learned a few things into the bargain.
gavski
Posts: 21
Joined: Sat Oct 02, 2010 1:46 pm


Postby Felipe Stalvey » Mon Apr 09, 2012 5:13 am

Warum soll jemand der einen vernünftigen Test machen will ausgeschlossen werden? Es geht nicht darum einen Lampe geschenkt zu bekommen. Sondern das sie von 10 Leuten getestet wird. Die Diskusion nach dem M7 Forums-Test war so gut weil (zum Teil) die richtigen Leute eine Lampe zum testen hatten. Daher sollten gerade die berücksichtigt werden die einen guten Test hingelegt haben und diesen bei der M7R wiederholen wollen.

Just measured a drop to 2.496V, I'd say the brightness level is similar to my 'dim' ref pic. One more thing, I used a Fluke 87 to measure the voltages, while not as accurate as bench meters, I'd say its more than enough for this task. Looks like I'm SOL, board is multilayered, can't check traces, nor can I replace any one component.
Felipe Stalvey
Posts: 1
Joined: Mon Apr 09, 2012 1:45 am


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