Ring main tripped struggling to find cause

[Paddington]

32amp ring main tripped mcb and rcd overnight. Rcd will reset but not all the time, mcb will not reset. Unplugged everything in house and mcb still trips, but rcd ok now. 32amp ring main covers whole house and struggling to locate fault. I'm newly qualified and probably missing something obvious any helpful suggestions as next steps?

 

[sparksburnout]

What tests have you done?

 

[westward10]

When you say the mcb will not reset is it because you experience some kind of short/arcing or does the mechanism feel broken.

 

[Pete999]

32amp ring main tripped mcb and rcd overnight. Rcd will reset but not all the time, mcb will not reset. Unplugged everything in house and mcb still trips, but rcd ok now. 32amp ring main covers whole house and struggling to locate fault. I'm newly qualified and probably missing something obvious any helpful suggestions as next steps?

I see from your profile you have Test and Inspect Qualies, have you bothered to test the Ring Final Circuit (not called a Ring Main anymore RFC for short) Or are you just hoping that by unplugging everything you may find the fault? ideal in the first instance but the faults you describe warrants further comprehensive testing

 

[Andy78]

Test the circuit. Be mindful of possible permanently connected loads off the ring such as boilers, kick space heaters, electric fires, towel rails, outside lights, out buildings etc. and disconnect them to assist the testing.

 

[Octopus]

I've had a run of RCD "tripping issues" of late (none being of my making) and I think that the 18th edition should recommend RCBO's for socket circuits....

Back to the OP :

Disconnect L & N from CU, test L-N, L-E and N-E - record values (you need to do continuity first then IR)

"guess" where half way round the ring is and repeat proceedure... at the CU you should then have 1 good "side" and 1 "bad" side - split "bad" side again and repeat until you locate the fault.

Don't even think about linking L&N to earth as it WON'T help, or save any time

 

[Paddington]

I've had a run of RCD "tripping issues" of late (none being of my making) and I think that the 18th edition should recommend RCBO's for socket circuits....

Back to the OP :

Disconnect L & N from CU, test L-N, L-E and N-E - record values (you need to do continuity first then IR)

"guess" where half way round the ring is and repeat proceedure... at the CU you should then have 1 good "side" and 1 "bad" side - split "bad" side again and repeat until you locate the fault.

Don't even think about linking L&N to earth as it WON'T help, or save any time

Rfc connected to 32a mcb however also a radial connected as well when doing r1 rn continuity can't get reading (19.99) tried all combinations r2 reading is 374.9 which shows fault somewhere. Cross connects also giving 19.99 at socket, haven't attempted ir as prefer continuity readings first befuddled now as very new to this

 

[Octopus]

Best disconnect the radial and test that separately. High R2 readings could just be loose connections. The trip could simply be associated with a loose connection

 

[tony mc]

If you dont IR the circuit your not going to find the leg that is causing the fault.

I would test each leg on low ohms first as if its tripping the RCD chances are you will get a reading if not switch to K OHMS and so on!

It might be 3 radials placed into the MCB!

Is this a job or is it your own premeses?

 

[westward10]

If the mcb won't reset sounds like line/neutral or line/earth short.

 

[Pete999]

As Tony mc said it could be 3 radials crammed into the one cb