Getting 10v on Steel Capping

Isolate the mains & see what voltage appears then.
Do a IR test on circuits .

Capping on the surface does seem strange. Is it on an exposed brick wall where they thought it was getting plastered eventually?

What are you testing to? The earth bar at the consumer unit?

With the power off of course, you could IR test between each outgoing circuit and the capping to find continuity, but if you’re planning on replacing the capping with plastic trunking anyway, then forego the testing and just remove it carefully. You might just visually find a nailed cable or whatever.

I’ll just advise that, with a trainee tag, know your limits….

As @cliffed said. IR testing L and N together to the cpc bar is a good start. I was also going to suggest testing to the capping but was beaten to it!
I think I’d test anyway in case a cable has been pulled too tight and a Neutral is touching the capping. I’d like to know before swapping to plastic so I can see how bad it is and proceed accordingly.

or....stick a cople ofUSB sockets (in series) to the capping. wham bam 2 x 5V.

littlespark said:

Capping on the surface does seem strange. Is it on an exposed brick wall where they thought it was getting plastered eventually?

What are you testing to? The earth bar at the consumer unit?

With the power off of course, you could IR test between each outgoing circuit and the capping to find continuity, but if you’re planning on replacing the capping with plastic trunking anyway, then forego the testing and just remove it carefully. You might just visually find a nailed cable or whatever.

I’ll just advise that, with a trainee tag, know your limits….

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That probably makes sense regarding them thinking it’ll get plastered over as one wall in the cupboard is plastered over but the other isn’t

I was testing to the MET in this instance assuming there would be no difference to testing to the earthing bar in the consumer unit but I can do that next when I’m down if necessary

Yes and noted regarding knowing my limits

timhoward said:

As @cliffed said. IR testing L and N together to the cpc bar is a good start. I was also going to suggest testing to the capping but was beaten to it!
I think I’d test anyway in case a cable has been pulled too tight and a Neutral is touching the capping. I’d like to know before swapping to plastic so I can see how bad it is and proceed accordingly.

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Yes same here i’d like to know also before changing to plastic so will definitely complete some testing first

Thanks all for the suggestion (aside from the USB one ). I’ll complete an IR first and go from there

impish15 said:

I was testing to the MET in this instance assuming there would be no difference to testing to the earthing bar in the consumer unit but I can do that next when I’m down if necessary

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Correct - should be the same result.

I had an interesting fault a year or so ago when I’d completely disconnected two legs of a ring for testing and was getting voltage of about 15v between the two neutrals - my tester alerted me and refused to test.
It turned out to be a N snagged on capping and a N from another circuit that was live snagged on same capping.

timhoward said:

Correct - should be the same result.

I had an interesting fault a year or so ago when I’d completely disconnected two legs of a ring for testing and was getting voltage of about 15v between the two neutrals - my tester alerted me and refused to test.
It turned out to be a N snagged on capping and a N from another circuit that was live snagged on same capping.

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This is good to know. I’ll bare this in mind whilst I investigate

Capacitive coupling from the cable to the capping?

DPG said:

Capacitive coupling from the cable to the capping?

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Agree that's a possibility, especially if measurement being made with a multimeter?

You said:

I got a reading of 10v.

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Without specifying which two points the 10V was measured between. The capping and ?
Earth, we might presume but it should always be stated.

Did you expect there to be no voltage between the capping and earth? Is the capping connected to earth? If not, why would you assume them to be at the same potential? If the capping is not connected to anything, it is free to take up any potential it likes, 10V, 100V, 1000V to any other thing. But there is a small amount of capacitive coupling from it to everything around it and small currents can pass through the capacitive reactance to induce or remove a potential on the capping. It's the same principle that a Volt-Stick uses to sense voltage without a connection.

Most of the stray capacitance from the capping is to earthy things around it, so it will tend to take up an earthy potential. But if there are energised line conductors nearby, e.g. the enclosed T+E, there will be a small amount of capacitance to line. This works like a voltage divider and will pull the capping to a voltage between the two but much nearer earth than line. The actual voltage tells you little, other than that the capping is near some live cables. It's often called a 'ghost voltage' - it's still a real voltage but its source has such a high impedance that it is hard even to measure consistently.

Q: How would you go about distinguishing between:
A) 10V ghost voltage relative to earth, on a piece of capping that is genuinely floating, i.e. not in contact with any conductors, and
B) 10V relative to earth, on the same piece of capping that has come into solid contact with a conductor 10V from earth, e.g. where a fixing has hit a neutral conductor.

A) 10V ghost voltage relative to earth, on a piece of capping that is genuinely floating, i.e. not in contact with any conductors, and
B) 10V relative to earth, on the same piece of capping that has come into solid contact with a conductor 10V from earth, e.g. where a fixing has hit a neutral conductor

I'd start by using a "proper" meter:

telectrix said:

A) 10V ghost voltage relative to earth, on a piece of capping that is genuinely floating, i.e. not in contact with any conductors, and
B) 10V relative to earth, on the same piece of capping that has come into solid contact with a conductor 10V from earth, e.g. where a fixing has hit a neutral conductor

I'd start by using a "proper" meter:

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Ooh...drool....you tart! You'll be saying you have one for it next:

Lucien Nunes said:

Q: How would you go about distinguishing between:
A) 10V ghost voltage relative to earth, on a piece of capping that is genuinely floating, i.e. not in contact with any conductors, and
B) 10V relative to earth, on the same piece of capping that has come into solid contact with a conductor 10V from earth, e.g. where a fixing has hit a neutral conductor.

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Seeing as no one has answered, I think easiest is to disprove B with an IR test. Once B is eliminated it becomes A by default.