Strange French system

[Speedy Builder5Participant @speedybuilder5]

So,  I am replacing a 240volt A/c mains socket that has burnt out due to the securing screws for the cables becoming loose over the past N years.

There are two fuse boxes for each circuit in the house – I suspect that the original box only had a fuse in the Neutral line (curious French system) and a second fuse box was added below the old box which now puts a fuse in the Live side of each circuit.

To work on replacing the socket, I pulled both the neutral and Live fuses and was surprised that the neon tester showed both the live and neutral were still live !  A bit perplexed, I put a digital A/c meter across the two wires and got a reading of about 15 volts, and again 11 volts between earth and live or neutral respectively.

I believe that this socket (used for a 2Kw  immersion heater) is the only outlet on the circuit, so is the residual voltage just induced from other circuits that are in the proximity?

I can of course pull the main fuse as the power enters the building for total security, but just curious to know what is going on.

Bob

[Michael GilliganParticipant @michaelgilligan61133]

Very strange that a Neon tester lit-up with low voltages … way below the the strike voltage for any Neon lamp I have seen.

Perhaps David Noble [the magician] can explain.

MichaelG.

[Wink HackmanParticipant @winkhackman25989]

It’s induced voltage aka phantom voltage. Perfectly normal in an unconnected, floating cable that runs near to energised cables.  The neon tester btw is your worst friend. A Fluke voltstick is a much safer tool.

[noel shelleyParticipant @noelshelley55608]

Why not put a switched outlet in with a front  cable grip, or wire out from the mounting plate. Why use a plug at all ? Noel.

[Ian PParticipant @ianp]

Its a ‘curious French system’, probably best to go with the flow and stick to their norms.

Ian P

 

[Robert Atkinson 2Participant @robertatkinson2]

Either capacitively coupled (not “induced” or inductively coupled) from other wiring or, more likely, leackage across the fuse holder. If the digital meter reads 15V and is the typical 10 megohm input resistance the current is only 1.5uA so a leakage resistance of about 150 megohm. This is within aceptable limits. The neon tester lights becuase it’a un-struck impedance is much higher and 1.5uA is enough to make it glow.
You can get multimeters with lower input resistance on AC volts for electrical aplications. Fluke LoZ
https://www.fluke.com/en-gb/learn/blog/digital-multimeters/dual-impedance-digital-multimeters

This is not a fault and the circuit is safe to work on.

Capacitive coupling between wires in UK style two way lighting circuits can be enough to keep LED lights dimly lit.

Robert.

[Speedy Builder5Participant @speedybuilder5]

Noel, Many of the older installations have their water heater “plugged in”. When I enquired some years ago whilst I wired up our home, I was told it was for security during thunder storms of which we do get some crackers, especially when it’s hot. The belief was that if the overhead lines were struck by lightning, then the whole water system would become live and cause a fire! (No problem about the electrical circuits in the home ??).  A friend’s house had the incoming supply on a plug and a socket on the wall connected to the fuse box – yes, the pins of the plug were always live and exposed when unplugged. The home would be “un-plugged” during a storm (If you were home at the time).

In our region, it is a condition of the home insurance to have lightning protection as part of the electrical installation which cuts and grounds all circuits on lightning detection.

Robert, thanks for the guidance.

Bob

[NealebParticipant @nealeb]

Stayed in a Chambre d’Hôte in Normandy this summer. In the (apparently freshly decorated) bathroom, there was an unswitched socket mounted just above floor level – about 10cm to the right of the toilet pan. One way to improve the aim of gentleman guests…

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