Odd fault on ring main....your thoughts please!

[Dunx]

Called out to repair some cabling today. Cable Tv guy has drilled through the ring main cables, completely severed one and nicked the insulation on the other. Old metal clad CU with 4 rewirable fuses, all found intact but the 60A main fuse had blown. Hacked out the scene of crime and decided to do temp repair, checked the ring continuity and ok on L & N but no continuity on earth. Reconnected the three and retested and found that I had 8 ohms live to earth and same on neutral. Continuity still ok on L/N but none on earth. Disconnected and left a section that tested ok
It was nearly seven pm so we have left as a radial on 15a, can't quite get my head round it at the mo, any thoughts? Is it possible that the cable has been damaged elsewhere?

 

[Rauer]

Have u got sleeving on all the earths? Strip it down buddy!!!

 

[Hawk81]

The continuity could be broke anywhere on the ring. Going to be a case of split and test until you find the fault.

 

[baldsparkies]

Very likely yes. The PFC has let through and taken out the mainfuse PFC on a dead short woild mean the whole ring has taken a hammering, and with the csa of the cpc being smaller that will suffer, and show up any weakness at terminations throughout the install. Your going to need to investigate further to find your gremlin.

 

[IQ Electrical]

Called out to repair some cabling today. Cable Tv guy has drilled through the ring main cables, completely severed one and nicked the insulation on the other. Old metal clad CU with 4 rewirable fuses, all found intact but the 60A main fuse had blown. Hacked out the scene of crime and decided to do temp repair, checked the ring continuity and ok on L & N but no continuity on earth. Reconnected the three and retested and found that I had 8 ohms live to earth and same on neutral. Continuity still ok on L/N but none on earth. Disconnected and left a section that tested ok
It was nearly seven pm so we have left as a radial on 15a, can't quite get my head round it at the mo, any thoughts? Is it possible that the cable has been damaged elsewhere?

If a 60A fuse was blown, it's quite possible that the cpc has blown apart somewhere along the circuit, possibly damaging the insulation on L+N at the same time!

Did you do any IR testing?

 

[baldsparkies]

Your thread shows one of the many advantages of RCD protection. Classic stuff.

 

[Dunx]

Yep I am back am and will split and test.... No point in doing IR when its 8ohms to earth! Agree absolttely re RCD's! Apparently the cable guy was an electrician....and he walked!