Strange Voltages

Guardamar · 25 May 2015

Would appreciate some help please.
Have just wired up two ceiling lights to come on from one wall switch, and they work great, but, when the switch is off, in the junction box I have the following:

Between live and earth = 130v

Between Neutral and earth = 100v

So between my live and neutral wires that connect into the light fittings, I have 110v with the wall switch off?

Guardamar

Taylortwocities · 25 May 2015

How are you measuring that, and with what device?

Multimeters are very very high impedance and will aslo measure any induced voltages. Try that measurement again with a shunt load across the meter input, and you will see a big fat ZERO.

Lectrician · 25 May 2015

Lost earth, either in your alteration or in the circuit feeding it. It needs sorting.

JohnW2 · 25 May 2015

Guardamar said:
Between live and earth = 130v
Between Neutral and earth = 100v
So between my live and neutral wires that connect into the light fittings, I have 110v with the wall switch off?

What live-earth and neutral-earth voltages do you see with the switch 'on'? (and the circuit connected to a light fitting with lamp/bulb, so that it lights up)?

Kind Regards, John

ericmark · 25 May 2015

It sound like no earth but question is what do you consider as being earth?

Up to the 1966 you were allowed lights without an earth connection and many houses still today have no earth to light fittings.

Personally I consider this as unacceptable every house should be tested every 10 years so at least 5 times the owner should have been notified.

Although the IET (was IEE) regulations of before 1966 permitted no earth the IEE and BSi only produced joint regulations in 1992 so as far as BS7671 goes lights have never been permitted without earth connections.

However it would seem the "Electrical Safety Council" still give advice to electricians about what to do when there is no earth stickers on consumer units, Use of only Class II equipment etc.

It is a major undertaking to correct and it would seem this is considered when giving advice. In real terms it means you are restricted in what you can do. No metal fittings or switches.

deadshort · 25 May 2015

Thanks for the history lesson ericmark

how does that help the OP ?

If there is no earth continuity you must have it checked as this is potentially dangerous

is the correct answer ?

DS

securespark · 25 May 2015

The OP could check continuity with the MM between a socket's earth pin and the light switch earth wire.

Obviously, if there is no earth wire in the switch, that would sound the alarm for either rewiring or making safe with Class II, nylon fixing screws for switches (unless the boxes already have nylon lugs).

deadshort · 26 May 2015

Or even better check for continuity between the Light switch and MET

Regards,

DS

JohnW2 · 26 May 2015

deadshort said:
Or even better check for continuity between the Light switch and MET

Strictly true but, in reality, it's very unlikely that there would be continuity between the CPC at a light switch and the CPC in a sockets circuit other than 'via the MET' (or, at least, via the CU, if there were a MET external to the CU).

Kind Regards, John

Lectrician · 26 May 2015

deadshort said:
Or even better check for continuity between the Light switch and MET

Regards,

DS

You could, but a socket, or even a radiator would be more than likely closer.

**If the radiator does not show continuity to the lighting circuit, don't assume there isn't. The radiator may not be "earthed".

Taylortwocities · 26 May 2015

All of my radiators are connected up with HEP2O, so no earth there..

Earth pin of socket much more reliable IMO.

deadshort · 26 May 2015

You miss the point, which is a bit of a concern

Regards,

DS

JohnW2 · 26 May 2015

deadshort said:
You miss the point, which is a bit of a concern

I doubt that your point has been missed. However, confirming that the CPC of a lighting circuit has continuity with the MET, as well as continuity with the CPC of a sockets circuit, would probably only really be useful additional information if one also ascertained (which the OP probably couldn't) that the MET itself is actually connected to an adequate earth.

Kind Regards, John

Lectrician · 26 May 2015

deadshort said:
You miss the point, which is a bit of a concern

Regards,

DS

I doubt it, but thanks for the concern.

This is a DIY forum, and DIY advice is being offered. A quick way to check for an earthing by "belling out".

Even if you measure the resistance from the light switch to the MET, further tests would need doing to confirm an earth at the MET exists.

JohnW2 · 26 May 2015

Lectrician said:
I doubt it, but thanks for the concern. ... This is a DIY forum, and DIY advice is being offered. A quick way to check for an earthing by "belling out". ... Even if you measure the resistance from the light switch to the MET, further tests would need doing to confirm an earth at the MET exists.

Quite so - but you typed too slowly

As I originally responded to DS, although what he said was strictly true (albeit he didn't mention also having to make sure that the MET was adequately connected to earth), the chances of the lighting circuit CPC having continuity with a sockets circuit CPC without either of them having continuity with the MET must be incredibly, perhaps 'vanishingly', small!

Kind Regards, John

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Strange Voltages

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