testing for drilled cable

[Robbob1991]

After fitting a new shower and 10mm cable going to it, i think there could be a strong chance that the person that fitted a grab rail might have drilled through it or atleast broken the insulation on it.

I was just wondering how we could test to see if it had been or not. We have a multimeater and a Seaward Powertest 1557 to check it, but not sure how to test it.

 

[ColJack]

flash test it... though you don't have one of those..

megger it?

the only reall way to be sure it to remove the rail and the plug and the tile and look... sorry..

 

[PrenticeBoyofDerry]

If you IR(insulation resistance test it/megger) That will tell you if there has been major damage to the insulation of the conductors.
If do a continuity test that will tell you if any conductors have been broken.
If you get a low reading on the IR test, then remove the screw you believe has caused the damage the reading may change when retesting, that will give you a fair indication that is where the damage has occurred.

 

[bernardgreen]

If do a continuity test that will tell you if any conductors have been broken.

But it will not tell you if a conductor has been damaged and now has a reduced cross section area at the point of damage. That thinned section will become a hot spot when under load.

Insulation resistance tests will only give sensible results about the damage to the insulation if the screw and adjacent wall is included in the circuit. The insulation between conductors could test as OK while the Live conductor is in direct contact with the screw.

Removing the tile and inspecting is the only way to be 100% certain.

Otherwise turn the power off, remove the screw, squirt salty water into the hole and allow to soak the wall behind the tile, replace the screw and then test for insulation resistance between the screw and each of the conductors. That is still not not a 100% reliable test of safety.

 

[JohnW2]

If you IR(insulation resistance test it/megger) That will tell you if there has been major damage to the insulation of the conductors.If do a continuity test that will tell you if any conductors have been broken. If you get a low reading on the IR test, then remove the screw you believe has caused the damage the reading may change when retesting, that will give you a fair indication that is where the damage has occurred.

All true - and, indeed, one could also do a continuity test between the screw head and each of the conductors of the cable. However, as Bernard has said, none of this will identify 'minor damage' which could nevertheless represent a potential danger in the future. I really don't think there is any getting away from the fact that if one has good reason to suspect that the cable has been damaged, one has no choice but to expose and inspect it.

Kind Regards, John.

 

[holmslaw]

..

 

[xr4x4]

If the screw has gone into the live, the screw will be live.

If the screw has gone into the neutral or earth, the screw will be earthed.

If it's gone into more than one, the rcd should trip.

Test with a multimeter.

 

[JohnW2]

If the screw has gone into the live, the screw will be live. If the screw has gone into the neutral or earth, the screw will be earthed. If it's gone into more than one, the rcd should trip.
Test with a multimeter.

All true, but as Bernard, holmslaw and myself have all said, even if none of those things has happened, there's no guarantee that potentially dangerous damage has not been done to the cable. If there is reason to believe that the cable may have been damaged, the OP must either de-energise the circuit and never use it again or else expose and visually inspect the cable ... or 'gamble', which is not an approach any sensible person would take, particularly in a bathroom.

Kind Regards, John.

 

[holmslaw]

..

 

[xr4x4]

If the screw has gone into the live, the screw will be live.

If the screw has gone into the neutral or earth, the screw will be earthed.

If it's gone into more than one, the rcd should trip.

Test with a multimeter.

That is not a solution and proves nothing of any value. The hole could have been drilled and damaged a conductor, you then fit a plastic wall plug that fills the void made by the drill and insulates the screw. But the current rating of the cable has been reduced perhaps to the point where the wall plug melts and the screw becomes live.

The only solution is digging it out for visual inspection.

You are quite correct, I didn't think of that.

 

[securespark]

or 'gamble', which is not an approach any sensible person would take, particularly in a bathroom.

I've played poker in the bath before....is that dangerous?

Seriously, is the cable in a safe zone?

 

[westie101]

In actual fact a good TDR with a trained operator could possibly detect a change on impedance.
But as a decent TDR costs about £3000 it is probably better just to dig it out!

 

[JohnW2]

I've played poker in the bath before....is that dangerous?

Very probably, but in a different sense

Seriously, is the cable in a safe zone?

Whether it is or not, the OP obviously thinks that the cable and the screw are in at least fairly close proximity - so the answer to the question would only be useful in knowing whether to 'blame' the cable installer or the grab-rail installer (or both!)!

Kind Regards, John.

 

[JohnW2]

In actual fact a good TDR with a trained operator could possibly detect a change on impedance.

If it did detect a fault, one would have to excavate the cable to replace/repair. If it didn't detect a fault, no matter how good the TDR and operator, I would suggest that it would be irresponsible to assume that the cable had not been damaged in some way that could result in a dangerous fault arising at some point in the future - so, again, I think one would have to 'expose and inspect'. I therefore doubt that the TDR would actually make much difference to the exercise.

Kind Regards, John

 

[Lectrician]

Does make you wonder if the cable was in safe zone...