37v present in switched off lighting circuit!

[Leedsposter]

My house was professionally rewired in 1997. I recently replaced 8 individual kitchen R60 spots (2 circuits) with 4 sets of 3xGU10 spots. These came with halogen and all worked as expected. I recently replaced these with LED spots, and in one circuit I notice that the leds are still (very dimly) lit even when the switch is off. If I replace one of the leds with a halogen, then there is no glimmer, but it returns as soon as i take the halogen out. If I take out one led spot, and measure the voltage with a digital voltmeter, I get either get a reading or a few volt (<10) which then drops to 0 very soon, or sometimes I get a constant 37v reading.

I'm baffled! Any suggestions? Should I get this investigated? Apart from the very low cost of the electricity used (the leds are 4w each and presumably only draw 0.6w each when "off", so about 5.5kw/year for 6 of them), tI don't really mind about glimmer. I've checked all switches and nothing obviously amiss.

Thanks

 

[skenk]

Sounds like capacitive coupling/phantom voltage, there is a very small amount of current induced by live cables running parallel to the (switched off) switch cable. This is enough to light the led's a little as they don't need much. (if it's this) it's normal and nothing to worry about (although maybe slightly annoying!) Are the lights controlled by two or more switches by any chance?

Someone else may be able to explain better

 

[Leedsposter]

Sounds like capacitive coupling/phantom voltage, there is a very small amount of current induced by live cables running parallel to the (switched off) switch cable. This is enough to light the led's a little as they don't need much. (if it's this) it's normal and nothing to worry about (although maybe slightly annoying!) Are the lights controlled by two or more switches by any chance?

Someone else may be able to explain better

They were originally controlled by 2-way switches; but in late 90s I fitted a dimmer switch, so rewired one of the switches so both-ways on and put the dimmer switch on the other one. When I fitted the leds, I had to remove the dimmer switch of course and put back a regular switch, but all the cable work is still there, so it could be a capacitance coupling (I had wondered about that). The second lighting set is free of this issue, so it's a bit odd (both are controlled by the same double switches), but the cable runs will be slightly different (though I'd be surprised if there was another cable which only ran parallel to the second set.

 

[Taylortwocities]

The two-way switching will be connected by 3-core and earth cable.

Make absolutely sure that the earth (cpc) conductor of all cable involed are actually connected to earth. If you miss an earth out then it can cause the problems that you describe.

PS When you say

My house was professionally rewired in 1997

on what basis do you describe "professional" does that mean that they did the work for reward, or were they Professors of Domestic Wiring?

 

[Leedsposter]

The two-way switching will be connected by 3-core and earth cable.

Make absolutely sure that the earth (cpc) conductor of all cable involed are actually connected to earth. If you miss an earth out then it can cause the problems that you describe.

Thanks for this; will check tomorrow once it's light.

PS When you say

My house was professionally rewired in 1997

on what basis do you describe "professional" does that mean that they did the work for reward, or were they Professors of Domestic Wiring?

It was an electrician whom I contracted via the builder who was doing some internal renovations at the time, and having just bought the house and having had a full structural survey recommending a rewire, that's what I did. I confess I didn't check his certificates...

 

[ban-all-sheds]

I recently replaced 8 individual kitchen R60 spots (2 circuits) with 4 sets of 3xGU10 spots. ... I recently replaced these with LED spots.

Are you happy with the way 12 2" LED lamps illuminate the kitchen?

 

[Leedsposter]

I recently replaced 8 individual kitchen R60 spots (2 circuits) with 4 sets of 3xGU10 spots. ... I recently replaced these with LED spots.

Are you happy with the way 12 2" LED lamps illuminate the kitchen?

Yes I am; I spent a long time wondering which ones to get and whether they would be bright enough. (I didn't want spend as much as the new ones costing around £20 each). I originally had 8x60w incandescent. Now I have 12x4w led and they are at least as bright. Slightly pinker in tinge. The ones I went for eventually are ones I bought on ebay with 80 leds each. They give at least equivalent light as the old incandescents but probably slightly less than the halogen 50w.

 

[Leedsposter]

The two-way switching will be connected by 3-core and earth cable.

Make absolutely sure that the earth (cpc) conductor of all cable involed are actually connected to earth. If you miss an earth out then it can cause the problems that you describe.

I checked: all earths are connected together within the switch boxes. I assume that the earth from the distribution box is connected to actual earth! (Though this is a 1997 installation so, as I understand, there was then no need for an actual electrode into the ground; I can see a bond to the gas pipe and one other earth wire leaving the distribution box, which presumably goes to a water pipe though I can't spot where.)

 

[Steve]

(Though this is a 1997 installation so, as I understand, there was then no need for an actual electrode into the ground; I can see a bond to the gas pipe and one other earth wire leaving the distribution box, which presumably goes to a water pipe though I can't spot where.)

Earting via utility service pipes hasnt been allowed since the 14th edition IIRC (30-40 years ago)

Your main earth will either be TT (earth rod), TNCS (connected to the neutral at the main fuse cutout), or TNS (connected to the sheath of the supply cable or a seperate earth cable underground)

If you have TNCS (the best type of earth for domestic) there will be PME stickers on the mainfuse.

The earths to the pipes you see are actually main bonds, which stop them from introducing potential voltages into the house (the equipotential zone).

 

[Leedsposter]

(Though this is a 1997 installation so, as I understand, there was then no need for an actual electrode into the ground; I can see a bond to the gas pipe and one other earth wire leaving the distribution box, which presumably goes to a water pipe though I can't spot where.)

Earting via utility service pipes hasnt been allowed since the 14th edition IIRC (30-40 years ago)

Your main earth will either be TT (earth rod), TNCS (connected to the neutral at the main fuse cutout), or TNS (connected to the sheath of the supply cable or a seperate earth cable underground)

If you have TNCS (the best type of earth for domestic) there will be PME stickers on the mainfuse.

The earths to the pipes you see are actually main bonds, which stop them from introducing potential voltages into the house (the equipotential zone).

Thanks for this. No sticker on the main circuit breaker box, so presumably not TNCS; Of the green/yellow wires leaving the breaker box, one goes to the gas pipe, the other goes up to the garage ceiling, and then I know not where!

In any case, back to the original topic of the post, it sounds like it's just a capacitive coupling/phantom voltage and not something to worry about.

Thanks to all for the informative replies.

 

[Leedsposter]

... hmm... actually it may be TNCS, but unlabelled (no safety sticker on the gas bond either). See:

Untitled

• Leedsposter
• 28 Feb 2010
• 1

though I was expecting the earth to neutral connection to be done at fusebox, not the other side of the meter.

 

[sparkiedave]

Is that a clamp I see under the meter going onto the sheath of the supply cable?

 

[Steve]

The earth is NEVER connected to the neutral WITHIN an installation. It is ONLY ever done within a sealed cutout and at the DNO substation/transformer.

The box below your meter is a cutout, it conatins the main fuse. You cannot touch this box as it is sealed with tags by the DNO. And see the green and yellow going into the top of it, next to the neutral? This means its TNCS.

BUT you also have an earth clamp on the supply cable. Which is TNS.

Odd, but not unheard of. Dont worry about it.

 

[Leedsposter]

The earth is NEVER connected to the neutral WITHIN an installation. It is ONLY ever done within a sealed cutout and at the DNO substation/transformer.

The box below your meter is a cutout, it conatins the main fuse. You cannot touch this box as it is sealed with tags by the DNO. And see the green and yellow going into the top of it, next to the neutral? This means its TNCS.

BUT you also have an earth clamp on the supply cable. Which is TNS.

Odd, but not unheard of. Dont worry about it.

thanks for this. I'll stop worrying

PS Here's a closeup of the two clamps:

Untitled

• Leedsposter
• 28 Feb 2010
• 1

 

[Spark123]

It looks like some sort of TN-CS conversion done by the DNO, possibly to earth the sheath of their supply cable. There doesn't appear to be any of the earthing leaving the supply head area to your side of things so you could quite easily be on a TT system.
Can you post a pic of your consumer unit?