Puzzle over a lighting circuit with no CLC

[Wizbit]

Wonder if anyone can help my poor brain on this one...

Situation..domestic, house, 1955, full of every single elec DIY nightmares courtesy of owners in the 90s.
Lighting circuits have no cpc, but in doing a DIY attic conversion at some point, previous owners put pretty metal lights up and a metal switch..oh yay..they want a new CU so going through all the usual checks.. I opened them all, all have a cpc..but in doing a Cont check between MET it was apparent that these cpcs are not actually connected to anything..all open circuit.
I had done the Cont test with the MS off...but I happened to do it today with MS on, but lights off,,,suddenly getting a Voltage reading of 36V between the MET and the metal (and cpc) of each light and switch!!.. With the light turned on reading went up to 118V...same at every light.
Help!! Does this mean that the Cpc from these lights IS loosely connected to something somewhere? (It's certainly not picking up an earth from any sockets etc but I fear many a hidden JcnBox in the property..)
or is this some kind of induction going on?
I should say the MET leads to a Rod as it's a TT..rod of about 100ohm, bonding in place takes the Ze down to about 2.5ohm.

Any ideas much appreciated! Many thanks

 

[Wizbit]

Sorry, didn't mean 'Ze' in last line..meant 'average' Zs readings..

 

[HandySparks]

Almost certainly an induced voltage. Try an analogue meter or a test lamp. Nevertheless, it needs connecting to the MET pronto!

 

[Wizbit]

Almost certainly an induced voltage. Try an analogue meter or a test lamp. Nevertheless, it needs connecting to the MET pronto!

Hmm, I wondered that..but I also tried it to the earth of the nearest Ring Final socket and got exactly the same voltages..?

 

[HandySparks]

Hmm, I wondered that..but I also tried it to the earth of the nearest Ring Final socket and got exactly the same voltages..?

If you're saying that you're measuring between the floating lighting cpc and the earth pin of a nearby socket, then that's what you'd expect, as the socket earth is connected to the MET.

 

[Wizbit]

If you're saying that you're measuring between the floating lighting cpc and the earth pin of a nearby socket, then that's what you'd expect, as the socket earth is connected to the MET.

Sure. What is confusing me is the first time I wanted to check if these lights and their cpc was truly earthed I just did a continuity test to the nearest earth pin, AND to the MET using wanderlead and got an open circuit. All other metalwork in the house nicely earthed. But today when I went to do the same test it tells me there's this voltage there..and as I say, to be as high as 118V when the light is switched on..could that still be induction?.. (I'm asking out of ignorance I should add!..

When I then used a voltage indicator to measure the v between L&E in the lights themselves I got a reading of 8volts.

 

[HandySparks]

But today when I went to do the same test it tells me there's this voltage there..and as I say, to be as high as 118V when the light is switched on..could that still be induction?..

Yes, I recon so. But it is a high impedance voltage, and if you load it a little (hence analogue meter or test lamp), it should drop to very low levels. ie, there's no great amount of current available.

 

[NickD]

If all those CPCs you've found are connected together, you have a pretty sizeable network running in close proximity to current-carrying 230V but not actually earthed to anything. You would expect some relatively impressive inductive pickup.

 

[snowhead]

Life was so much simpler when we only had Avo 8's and Martindale /Drummond style test lamps.
We had none of these "Faults".

 

[telectrix]

still got avo. 2 in fact.

 

[Engineer54]

From a 100 ohm TT earth, to 2.5 ohms with bonding in place ...Now that's impressive!!

 

[NickD]

Life was so much simpler when we only had Avo 8's and Martindale /Drummond style test lamps.
We had none of these "Faults".

Luxury. When I were t'lad down t'pit we 'ad to test by stickin' ower tongues onto t'terminals. Then go back t t'ole in road, get up an hour before going to bed, and father would slice us in two wi't'breadknife. If we were lucky!

 

[Geordie Spark]

Luxury. When I were t'lad down t'pit we 'ad to test by stickin' ower tongues onto t'terminals. Then go back t t'ole in road, get up an hour before going to bed, and father would slice us in two wi't'breadknife. If we were lucky!

We didn't get electric shocks off the gas lights either!

 

[snowhead]

Luxury. When I were t'lad down t'pit we 'ad to test by stickin' ower tongues onto t'terminals. Then go back t t'ole in road, get up an hour before going to bed, and father would slice us in two wi't'breadknife. If we were lucky!

An older workmate used to comment how stupid "That program" was, yet he had to watch it just to see how stupid it was.

If he hadn't watched it he wouldn't have had a clue what most of us were talking about.

10.

 

[7029 dave]

Life was so much simpler when we only had Avo 8's and Martindale /Drummond style test lamps.
We had none of these "Faults".

I have been told by one of our trainers, that I cannot use my drummond/test lamps anymore, because if any micro generation installs present test lamps will not pick up below 50v, must use approved volt meter.

 

[HandySparks]

From a 100 ohm TT earth, to 2.5 ohms with bonding in place ...Now that's impressive!!

A good long run of metal water pipe will beat most rods any day (even long ones ). My sister's place is currently earthed by the water and gas pipes, and the Zs at the sockets is around an ohm.

I'm still awaiting the call to regularize the situation, but I won't push it unless I hear that the services are being 'upgraded' to polyethylene.

 

[trev]

Luxury. When I were t'lad down t'pit we 'ad to test by stickin' ower tongues onto t'terminals. Then go back t t'ole in road, get up an hour before going to bed, and father would slice us in two wi't'breadknife. If we were lucky!

Luxury!

 

[Engineer54]

I have been told by one of our trainers, that I cannot use my drummond/test lamps anymore, because if any micro generation installs present test lamps will not pick up below 50v, must use approved volt meter.

And if you ''DON'T'' work on any micro generation installs?? These cretin bloody college tutors these days, seem to like making up their own rules!!! Get in contact with the manufacturers of the ''Drummond Test Lamps'', and tell them that you cannot use their test equipment anymore, cause your tutor told you so and see what they have to say!! lol!!

 

[Engineer54]

A good long run of metal water pipe will beat most rods any day (even long ones ). My sister's place is currently earthed by the water and gas pipes, and the Zs at the sockets is around an ohm.

I'm still awaiting the call to regularize the situation, but I won't push it unless I hear that the services are being 'upgraded' to polyethylene.

Except for the fact that metal service pipes (Copper, Lead, Galv Steel) are generally not laid in the ground ''Bare''!! They will almost always be protected against corrosion!! The old provision, was something like a Denso tape product (a thick grease impregnated webbed tape) . So not exactly the best conductive medium to the soil!!

 

[7029 dave]

And if you ''DON'T'' work on any micro generation installs?? These cretin bloody college tutors these days, seem to like making up their own rules!!! Get in contact with the manufacturers of the ''Drummond Test Lamps'', and tell them that you cannot use their test equipment anymore, cause your tutor told you so and see what they have to say!! lol!!

That was my thought IF YOU DON'T. not gonnar argue with SSE trainers no point!!!. They only had me in for the day to update my MOCOPA cert. lol