the incredible live wires!

[loublou]

Hi
I'm replacing a defective socket. the earth was live.

Fed through new 3 core flex,fitted new socket, wired up new socket. All correct.

Wired live wire feed only. Tested earth and neutral. BOTH were live along with live.

Checked all again, same result. disconnected new socket and enured all bare wire separated, same result. Fed through new flex not once but three times, same result.

So, question is, how can all three wires become live when only one (live) is connected to anything and none of the wires are touching?

seems really weird to me.

ta

 

[ban-all-sheds]

1) I hope you were using 2.5mm² twin & earth cable, not flex.

2) How were you carrying out your tests? Did you use a proper multimeter?

 

[Paul_C]

How were you testing? Assuming you were using a meter, what were you using as your reference earth point? The earth at another socket, or a pipe maybe?

If you had the neutral and earth of the cable disconnected at both ends but the live connected, then with a digital meter (high impedance input) it would be normal to read voltages due to capacitive coupling in the cable.

That doesn't explain why the original socket had problems though. Have you tested the point at which this spur is run for proper earth continuity?

 

[loublou]

ta for your help folks. weirdness seems to be cool!

I may be missing something here, perhaps there's always some leakage between wires but I've never come up against this particular undesired distribution of power before. Personally I don't want to again. That's why it would be good to get a reason for it.

What's this 'it would be normal to read voltages due to capacitive coupling in the cable' about? I should say it is only 5 metres of cable.

I'm using a good, reliable test driver not metre though I do have one so shall put that on it to see what that may say. However if I can't trust a test driver while working than I'm in trouble!

ta

 

[AdamW]

You say you were using flex. Do you mean

or do you mean

 

[loublou]

the first, all protected, sheaved cores.

also solid copper, not strands.

are u really from vatican city state? as in the holyiest of well reputed sparkies?

 

[Paul_C]

the first, all protected, sheaved cores. also solid copper, not strands.

The first pic is of flex, which does not have solid cores and should not be used for fixed wiring. Do you mean that you have solid-core cable, like the second pic, but with the new brown and blue color coding?

What's this 'it would be normal to read voltages due to capacitive coupling in the cable' about? I should say it is only 5 metres of cable.

Any time you run two conductive surfaces close to one another, they exhibit an electrical characteristic known as capacitance. A cable has two or more conductors, running parallel, with just the insulation separating them, so you always get a certain amount of capacitance between the cores. It's also a characteristic of alternating current (the type supplied to your home) that it will pass through a capacitance.

In most general electrical work, this capacitance within a cable is too small to be of any great significance, but when you have a open-circuit conductor (i.e. disconnected at both ends) in combination with a meter which has a high input resistance, you will see the effects of this capacitance as a voltage reading on the meter.

Many modern digital meters have a very high input resistance wich will show the capacitive effects very well. I just picked up an offcut of 2.5mm T&E cable, about 5 feet long and connected it as you describe: Live to 240V power, neutral and earth wire left open at both ends. I then used a digital meter with 10 megohm input and read 130V to ground on the earth wire, 92V to ground on the neutral. I didn't bother to go any further, but had I then changed to a meter with a lower input resistance, the voltage readings would have been lower.

So you can see it can take only a very short length of cable to give substantial voltage readings. By "test driver" I assume you mean a screwdriver with built-in neon tester. As a neon light is also inherently a high-resistance device, it would be quite normal to get it to glow when touching the open conductors in the cable due to the capacitance.

BTW, for the technical guys here, I didn't bother to dig out my capacitance bridge to measure the capacitance directly, but a rough calculation from the measurements taken would suggest a line-to-earth capacitance in that 5 ft. of cable of about 200 picofarads.

 

[andy]

I'm using a good, reliable test driver

bin it. none are reliable. use a multimeter.

 

[loublou]

hmmmm, very interesting stuff. Ta

So I gather that I can expect such 'voltages due to capacitive coupling in the cable' from any cable?

Should I not be buying budget cable?

I'm surprised. I've never encountered it before.

I'm going to try the experiment and see.

I'm using solid copper, 3 core cable. all sheaved. I also tried three seperates, they did the same sort of thing. Only not using a meter I can't be precise.

And whenever testing use a meter. Seems a change of methods may be needed.

OK. Assuming this is to be expected, what are the implications? Here I am trying to get this working. Should I wire it up with such a 'voltage due to capacitive coupling in the cable' or not?

 

[Paul_C]

bin it. none are reliable. use a multimeter.

Hear hear!

So I gather that I can expect such 'voltages due to capacitive coupling in the cable' from any cable?

Yes. The highest quality cable in the world will still exhibit capacitive effects; it's just the laws of physics in operation. The amount of capacitance will vary depending upon the design and size of the cable, type of insulation, and so on, but you cannot remove it completely.

The small amount of capacitance is of no importance to the normal operation of your home's electrical system. When the wires are connected to the supply, to earth, or0 to appliances, that tiny capacitance is irrelevant compared to the relatively low resistances in the rest of the system. Your neon was glowing (and my meter registering up to 130V) only because the wires being tested were not connected to anything else at the time.

OK. Assuming this is to be expected, what are the implications? Here I am trying to get this working. Should I wire it up with such a 'voltage due to capacitive coupling in the cable' or not?

From your first post, it seems that you had a missing earth on the socket. The fact that replacing the cable from there back to wherever it was fed from and there was no change suggests that you have missing earth somewhere else.

I'd go back to the point where this spur is connected, and check for earth continuity there. If you don't have an earth there, it's time to trace the circuit back until you find the break.

 

[dingbat]

I'm using solid copper, 3 core cable. all sheaved.

Sorry about this, but I have to comment. You mean sheathed. In fact, you mean insulated - when we talk about cable the sheathing is the second layer of insulation that protects the whole cable from abrasion, whereas the inner pvc sheaths are used for both insulation and conductor identity. Pedantic, I know, but sometimes even the smallest typo/spelling mistake can make all the difference.

 

[loublou]

Pedantic, I know, but sometimes even the smallest typo/spelling mistake can make all the difference

Ok, a fair cop, all solid copper, all insulated, all wrapped in a sheath.

Low cost cable, I may source some better.

I maybe would expect this over a long length but only 5 metres surprises me and like I say it's not something I've encountered before.

Also need to learn how to use the meter a bit more to get its full potential.

Quite right above the earth, It's the earth that was the original problem and I've traced that back. Live neutrals are common place in this particular house, live earths a rarity.

As the socket has a water feature running off it had to have attention after I got a thrilling tingle while cleaning it one day.

I'm not going to set it back up until I'm absolutely happy with the earth.

Thanks for all your help folks, technical, pedantic, whatever. All good stuff and thanks for the time.

 

[jenki]

It's the earth that was the original problem and I've traced that back. Live neutrals are common place in this particular house, live earths a rarity.

AND

As the socket has a water feature running off it had to have attention after I got a thrilling tingle while cleaning it one day.

WTF

 

[AdamW]

Might I recommend that you head down to your nearest Red Light district and buy yourself a rubber suit and a pair of wellies?! Wear it whenever you are in the house until the problem is fully sorted!

Getting a tingle off a plug socket, whether or not it is used for a water feature, is NOT normal! It indicates a problem either at the water feature, socket or elsewhere.

It sounds like you really need to get yourself a meter, and figure out why you are getting these problems. If you still have your live neutrals and live earths when testing with a multimeter, and can't solve the problem yourself, you really do need an electrician. Yes, they are expensive chaps to get in for any length of time, but electricity kills and yours has already given you a nip for starters!

Perhaps a previous owner has bodged up seriously, perhaps something somewhere has failed? Not your fault granted, but it doesn't make it any less dangerous.

 

[mapj1]

Before you panic and do indeed start looking for rubberised undies.. perhaps some more explanation. I apologise now for noddyfying it a bit, but I think you will appreciate it.
What these neutrals and earths that appear to be live really mean, is that the neutral (or earth) is not really making a good low resistace metallic path back to the supply neutral (or earth). The cables then are free to float electrically speaking (being not properly making contact at either end) and pick up charge (similar capacitive effects occur with static electricity, rubbing balloons on dry cats and sticking them to the ceiling etc. - it only works when things are insulated - in normal house wiring the metallic cores are normally positively connected to something.)
As previous writes have observed, normally when everything is connected back to source, this capacitance is not noticable. However, if your neutrals really were live, or even just floating disconnected, then appliances plugged in would not work, as there would be no way for the current ot get home. I presume this is not the case? A test light should light if wired between live and neutral, or between live and earth (though this will trip the RCD if you have one), but not between neutral and earth, as these are at practically the same potential.
you are looking for a disconnection, between the last point on the circuit where this is true, and the first point where it is not, probably upstream of the socket itself. Dont rule out the possibility it may be wired wrong in the first place.
M.