Rewiring N1

[monmaison2009]

Hi,

I am putting back the original ceiling rose in my property (it was removed by the previous owner), when removing the new plaster I have found some electrical cables ( I could not believe my luck !) so I arranged for the electrician to come and check everything was ok ....
In short it is not, apparently the electrical cable leaks electricity so even when the wall switch is off there is still 50 Kw running through, apparently this is a no no (risk of electric shock)
The bad news is that to put a new cable part of the original lime plaster in the ceiling has to be removed and a groove made in the ceiling beams to run the cable .... :?

I was wondering if any of you had to do something similar and if there is any alternatives with minimal impact

Thank you very much for your help and advise

 

[88v8]

If there is 50V (not 50kw that would melt the house) the fault is in the switch not the wire. Electricians love to find 'faults', jobs for the boys. Although sometimes the faults are real of course.
Buy a dvm then you can check for residual current yourself, don't need an electrician for that.

I'm in the process of removing the lovely and perfectly good brass switches from our house to help sell it, as they're daaangerous :shock: or at least numpties think they are. Said switches will be going into our next house.

If you want switches that look the part - of course you do - it's a lot easier than when I started 30 years ago, here's a brand new one that looks 100 years old, or at least it does unless you compare side by side.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=400231141848&ssPageName=STRK:MEWAX:IT

It's made by Clipsal, who make a range of repro switches and sockets.

Anyway, to get back to your cable situation, if it really does need replacing can't you get above the ceiling, why does it have to be hacked in from below?

Ivor

 

[monmaison2009]

@ 88v8

Thanks for your quick response.

The electrician changed the switch and then tested again, could it be a possibility that the replacement switch is also gone?!
He also said that it can be possible that the cables are tangled and electricity is passing from one cable to another, is this possible?

You say sometimes the "faults" are real, is there a way to know this or do I have to trust what he says? Where can I buy a dvm?

Sorry for the amount of questions, as you can see I am quite reluctant to cause so much destruction unless it is a real "danger" :shock:

 

[MdB]

If the electrician said 50kW, get yourself a new electrician. If he said 50V then this could be capacitive coupling in the wires which indicates that the earth wire isn't connected - very common for old lighting circuits. If this is the case, the current that can be supplied this way is tiny and will occur no matter what age the cable. It could be something else but I think a second opinion is worth getting before doing a lot of work.

 

[monmaison2009]

@ Mdb

Thanks, the 50Kw is my mistake , he said 50V, is it possible to easily earth this cable thus avoiding having to do this work?
He thinks this current 50V is above the safety limits and if I plan on having a chandelier light there is a risk of electrical shock as the chandelier will have a lot of metal ....

I will ask for second opinion, I fear the "new" electrician will say something totally different

 

[MdB]

The 50V doesn't mean anything by itself.

I have just measured (*) the voltage coming out of 4.5V nokia phone charger I have here and got 40V! Out of the land line 6.5V power supply was 25V and best of all out the end of my finger was 50V! I am sure I could find equally silly voltages in your house. They are all real voltages but are all perfectly safe - even if they were considerably higher.

Not having an earth wire connected though is more of an issue though (and I'm not saying that you do - it is just a possible cause of the stray voltages). If you have one wire without it connected, I would suspect that none of your lighting has it connected. It isn't ideal but many houses are like this (mine was). The earth wire is likely to be in all the cables but may be chopped off short making it difficult to use. A complete rewire is the best solution but a cheaper solution would be to fit RCBOs to the circuits affected - £20 each plus fitting.

From what you are reporting, I'm suspicious that either the electrician doesn't know what he is talking about or he is trying a fast one. Get a second opinion.

(*) I say measure but I am of course measuring these voltages incorrectly. A voltage is measured between two points in a circuit. In my "measurements" I am only making one contact. The circuit is being completed via capacitive coupling (I think - it could be inductive) to the mains supply around me which is what is introducing the silly voltages I am measuring.

 

[88v8]

@ 88v8

He also said that it can be possible that the cables are tangled and electricity is passing from one cable to another, is this possible?

Where can I buy a dvm?

Tangled, yes but only if the insulation is gone, then you'd have 240V not 50V.
Is it PVC or rubber?

There are no earths in my lighting circuit as my olde switches (that I installed 30 years ago) don't have provision for earthing. So.... ? So nothing...
Another way of determining the lack of an earth is if you have brass switches, sometimes the covers seem to hum/vibrate, which is an inductive effect as Mdb says.

If you ask any electrician he's bound to say it's dodgy just to cover his ar.... posterior.

You can get a dvm here
http://www.screwfix.com/c/electrical-lighting/multimeters-clamp-meters/cat880004

#34612 will do you.

Or your local electrical retailer.

Btw, there are wooden chandeliers..... :wink:

Ivor

 

[Lime]

A digital voltmeter is not used for testing.
You want an insulation and continuity tester.
http://www.sercal-testequipmentsales.co.uk/insulation--continuity-testers-148-c.asp
What type of cable did you find in the ceiling?
PVC, rubber or what?

 

[Keithj]

I wouldn't use a DVM. I don't even own one. My brain is seriously analogue, and I prefer my Avometers. To test the safety of mains wiring, I use a Megger tester (a prehistoric but very useful device).

I would be VERY wary of doing your own electrical work unless you know what you are doing. It's very easy to kill yourself or others if you get it wrong.

If you are getting 50v through capacitative (or inductive) leakage, then you do need to fix it. That is likely to mean adding an earth wire if there isn't one. Trouble is, once an electrician starts pulling wires, he has to comply with all the new regulations - brown and blue cable, yellow/green striped earth wire, etc. As long as he leaves the existing wiring undisturbed, he doesn't need to do that.

Could he, perchance, use the old wire to pull the new wire through, so avoiding all the channelling of plaster etc? Or is the old wire plastered in?

 

[MdB]

If you are getting 50v through capacitative (or inductive) leakage, then you do need to fix it.

Why?

The few uA it could source aren't going to harm anyone and as I've posted above how do you propose fixing the 50V that is coming out of my fingers as I type?

(A missing earth wire I would consider mitigating with an RCBO but I wouldn't start replacing wires unless easy to do)

 

[Lime]

So far I think there is insufficient information to understand what relevance the 50 volt reading means or implies.
If I were testing this circuit I'd give a test report using resistance values not volts.

 

[Keithj]

If it's 50v at a microamp, then it won't do anyone much harm. However, when my wife got a tingle off the porch floor, and my Avo said 60 volts, it was indicative of the "protective multiple earth" coming into the house being connected to one of the phases. Her 60 volts was through damp in the floor of the porch, compared with damp in the floor of the hall. The current available in that area was a few milliamps - enough to be unpleasant. Had she touched an "earthed" appliance and a water tap, the result could have been serious.

You just don't know. I can get an indication of about 3KV off two different pieces of equipment in my workshop. One is harmless, one will kill you.

 

[Zebra]

I don't see any reason to think that your electrician is talking rubbish or trying to make work for himself, and I wouldn't suggest doing your own testing unless you know what you're looking for. If the current is leaking from one conductor to another then it sounds like the cable's insulation resistance is shot to pieces, i.e. the separate conductors in the piece of cable are no longer well separated, i.e. the cable is perished. Is it old looking cable? I doubt it's the switch if he's changed it.

There's no way of lifting the floorboards from above then, to install new cable? Unfortunately using the old cable to pull a new one through never works. It always turns a corner or goes through a tight hole. I suspect though it's not just this fitting that's affected, it may be the whole circuit. Old houses can be cans of worms electrically!

If the light point has no earth then you must not fit metal fittings or switches. It's the earth that makes it blow the fuse/trip the circuit breaker in the event of a fault, and so there would be a shock risk having metal fittings with no earth. You could run a separate earth to this fitting but it would be as much work as replacing the cable. Fitting RCBOs or RCDs on the circuit may make it safer, but it is against the Wirnig Regulations to have an RCD as the sole source of shock protection i.e. it doesn't mean you don't need an earth on metal fittings. If you have all plastic fittings and switches you can get away with not having an earth on the circuit, but only as long as the insulation resistance is healthy, which it sounds like yours is not, and only if you install warning notices at the fuseboard telling future occupants never to install metal swithces or fittings on that circuit.

By all means shop around for an electrician you trust, but I would think you need a electrician to do a Periodic Inspection on the house to tell you the full extent of the problem and the condition of your cabling. Houses should all have a Periodic Inspection every ten years anyway but very few do.

 

[MdB]

You just don't know

Agree totally. My point was that you need somebody that knows what they are talking about to check out the issue properly. You don't just start replacing stuff without finding what is causing the issue in the first place as it might not be a problem. Equally you don't just ignore it as it might be serious.

 

[monmaison2009]

Thank you all for your advise and comments.

The thing is I dont have a clue about electricity and the reason the electrician is giving me to replace the cable is not convincing enough (like the cables being "tangled", etc ). The cable does not look old (it is pvc), however I can not see the full extend of it to see if it has been damaged ...., he is using a dvm and I can see that when the switch is off around 50V - 55V are displayed. Another thing we found out is that if my neighbor upstairs switches his electricity off the main switch, that reading goes down to 24V (in the safety zone?! ) .... what that means I dont know

I have had a ceramic hob installed recently, the electrician who came to install it was happy with the installation and the only thing he changed was the fuse (for a bigger one, unfortunately he works for the cooker company only), plus I had an inspection down just over 2 years ago (all ok, to clarify the cable I am talking about here was hidden behind the socket and the ceiling plaster, we have discovered it when we removed the plaster to put back the original ceiling rose, so the periodic inspection will not have pick on that one)

 

[Zebra]

As Lime said above, a digital voltmeter is not used for testing. He needs to use a continuity and insulation resistance tester to test the insulation resistance of the cable, that is the only way to tell if the cable is sound. If you've had the rest of the house tested but this bit was missed, then this bit should be tested before putting it back into service. (Continuity and insulation resistance testers are much more expensive to buy than digital voltmeters but proper electricians would have one - perhaps you're right to have doubts about your guy after all.) "Tangled" doesn't make a lot of sense to me either.

 

[Lime]

From what you describe monmaison2009 the voltage is being picked up via capacitance (or inductance) between cables.
If they are twisted together the effect can be increased.

However it is a totally false "problem" and means nothing except that other cables are nearby.
The electrician is not testing the circuit correctly and (I presume) doesn't understand that he is using the wrong type of test and test equipment.

That does not mean that everything is ok... that can only be deduced by proper testing.
However IF the cable at the ceiling rose can light a lamp and the switch operates correctly then, in all probability, there is nothing wrong.
If the wiring does not have an earth wire at the ceiling rose you should not install any lamp or light fitting that requires an earth.

 

[MdB]

Just to prove my point, I've done a quick experiment here - I know what I am doing so this isn't one for others to repeat unless they do too.

I took my old 5m extension reel and measured the voltage between neutral and earth with the reel plugged into the wall and switched on but with nothing plugged into it. I got a figure of 0.06V which is what I would expect.

I then disconnected the neutral wire from the plug end such that the neutral wire was not connected to anything at either end. The extension reel obviously won't work like this but it is still completely safe. This time the voltage measured between neutral (not connected to anything) and earth was 105V!

This voltage is generated due to capacitive coupling in the cable and can be measured on my DVM. It is perfectly safe though as it can't supply any significant current - the capacitor value is far too small. It has absolutely nothing to do with failing insulation, rubbing conductors or anything like that - it is purely due to a disconnected conductor running parallel to a live wire.

However, as has been said before, there are other reasons why a voltage could be present and these could be potentially dangerous so it should be checked by somebody that knows what they are doing. I just would be surprised if this was the case.

-------

I was actually pleased to have done this test as when I took the back off the plug I found that one of the screw terminals was loose and that the cable clamp was done up too tight. I've been using this extension lead for years without noticing these faults

 

[Zebra]

Very interesting MdB...
Agree with Lime above, this could well be happening, but doesn't mean that the cable is or isn't safe, needs checking out properly.

 

[Flyfisher]

You just don't know

Agree totally.

That seems to be a fair summary so far.

In such a situation, where the consumer unit is effectively connecting to the unknown, I feel far happier having RCD protection. Such devices will provide far greater protection against the fault scenarios being guessed at than a simple wire fuse.

Having a modern CU with RCD(s) installed, together with an overall inspection and test, would be my starting point for ensuring the safety of the installation. Unless a 'hard' fault is found during this work then re-wiring - with all its associated disruption/destruction - should not be necessary. And if a 'hard' fault is found, well it needs to be properly fixed anyway, though it may just be one circuit rather than an entire re-wiring job.

"Tangled wires" makes no real sense at all as far as installation safety is concerned. I'd bet we've all got some degree of "tangled wires" in our homes. I would ask the electrician what he means by this and what problems such things might cause.