Electrical testing (Earth)

Steve formulated on Wednesday :

Yes, especially so with that length of cable.

Firstly can you not look at the other end?

Secondly do you want it to be grounded at the head end?

What is it powering, from where?

What sort of earthing arrangement is there at the supply end?

i.e. TN-S, TT etc - if that means nothing have a look at

if you cant work that out, then yes.

NT

Thank you Harry, this cable is being used to supply 240 ac to a gate automation, the system has been wired correctly ( completed last week ) and has been working fine until Monday evening when we had a terribile downpour, the rcd tripped at the main box, but once i removed the wiring , we were able to switch back on again. I suspected water ingress at 1 of the joints , which i did in fact find and took the corrective action by replacing the faulty gland, but still tripping rcd. I do however suspect that there maybe a o/loading problem and the addition of the gate's has triggered this. Sorry for this to be so long but really what i wanted to know was even as the system is earth through the 3 core , should i also ensure that the armour on the cable is returning to the C/unit and could the lack off trip the rcd. Many thanks Steve

Thank you

Thank you

It happens that Steve formulated :

All of which is not relevant to your original question. Your question now is how to check for some leakage or earth fault on the cable and/or what ever is connected at the far end of the cable. If the joints have not been correctly done or the gate equipment properly sealed against moisture, or the cable have been damaged during installation - then that would be enough to cause the RCD to trip. All that is needed to cause the RCD to trip is either L or N to have a leakage path to ground or earth.

Normal glands are not usually suitable for use out in the weather. Joints are normally made using a specially made for the job kit, which can then be quite safely buried. 100 meters can be installed in one piece in what would probably be a fairly small cable size(?), therefore no need for joints.

RCD's do not respond to overloads, that is what an MCB is designed to respond to. The extra load of the gate will be nil or minimal whilst not actually opening or closing.

The entire length of armouring should be be properly earthed, as should at least one of the cores.

From the little you have described of the installation, I would be concerned as to quality/safety of the installation.

Hi Thank you for your reply, i have checked wiring again and is correct, amoured cable is correctly earth and working, i have discover this a/noon that earthing to the gate motor's is the problem. As this is an u/ground system and the motors are sealed and encased in boxes i can only suspect that the amount of damp and mostiure around these case's is causing the rcd to trip. Let me add also that as a responibile person, i would never attempt to do shoddy work especially were electric is included, i have follow the manufactuers instruction to the letter, and pride myself in good workmanship. Again thank you for your input, and value opinion. Steve

this wont be whats causing the rcd to trip.

NT

Thank you for yor respsonse, but can you explain why when i disconnect the earths from the motor's in question, problem disappears !!. Thank you again

Would need to see the thing and test it to know, can only hazard a guess from here. First guess: there is earth leakage on the motors, perhaps due to water ingress. The motors are mounted on something nonconductive, eg wood posts perhaps, so when E is disconnected they sit there a danger to all who pass, but the rcd doesnt trip.

Either way, you do need someone that knows what theyre doing on this one.

NT

Hi again, you may recall i said these encased motor's sat in enclosed boxe's ( metal) i will h/ever take heed of your advice and call in the local Electrican. My concern would be that there maybe another underlaying fault within the electrics of this property. many thanks for your help