Hi,

Trying to test a SWA cable between the main consumer unit and a secondary consumer unit in the garage with integrated RCD.

The 40A fuse (breaker) in the main consumer unit keeps tripping even when the secondary consumer unit is switch off. I initially thought there was a problem with the fuse but swapped it over and still have a problem. I've tried completely disconnecting the secondary consumer unit and it still trips.

The SWA cable is terminated next to the main consumer unit in a junction box and if I disconnect it at that end the fuse is okay. So I'm thinking there is a problem with the SWA cable. How can I test it? Can I use a multimeter to make a simple resistance test between the conductors? Is this accurate? The SWA is 2 years old, about 15m long and buried under the driveway! :-(

Any other suggestions?

Thanks, Mark

Multimeter probably won't show anything up, you need an Insulation Resistance test or Megger to test the cable, they'll basically but 1000v down the cable to check for a breakdown in the insulation

you should disconnect the rcd at the secondary consumer unit just incase pushing 1000v down the cable, cream crackers the rcd, you should test between all conductor cables and the earthed armouring, any read you get over 2 megger-ohms is fine, if there is a dead short on the cable metre will most likely read 0.00 ohms

If its tripping the breaker i would have thought the simple test
L to N
L to E
N to E
with a multmeter should show up the problem and its going to be an live to earth fault

correct way would b with a insulation resistance tester

Testing with a multimeter doesn't show any problems. I'm borrowing a cable insulation tester at the weekend.

Mark