i am somewhat perplexed by a cable problem and would like to seek thoughts on it from users of this forum.
my daughter in law asked me if i would replace her exterior security light which she advised me had not worked for some years with a new one she had bought. the power for it is provided from a fused switched spur outlet in her bedroom. having switched off the power and removed the old light fitting i wanted to check the now exposed cable for functionality before fitting the new light so hooked up a multimeter between live and neutral, restored power and operated the switch - no power. removed fuse from front of switch - no fuse (no wonder it had not worked for some years). inserted new fuse switched on - flash, bang rcd tripped out. removed cable from switch thus isolating it completely. carried out continuity check end to end on all 3 cores - continuity confirmed. now for the perplexing bit - bear in mind cable is totally disconnected at both ends. at remote end of cable carried out resistance check betweem live and neutral - open circuit; between live and earth - open circuit; between neutral and earth - open circuit. repeated checks at other end of cable; live and neutral - 120 ohms; live and earth - 120 ohms; neutral and earth - 120 ohms.
the cable run disappears under the floorboards in the bedroom and i am going to have to trace it as soon as possible to find out what is going on. my daughter in law has no knowledge of when the fuse was removed and by whom.
any thoughts as to possible cause welcome as stated i am somewhat perplexed as to what could cause one end of a disconnected cable to read open circuit between live and neutral and the other end to read 120 ohms.
my daughter in law asked me if i would replace her exterior security light which she advised me had not worked for some years with a new one she had bought. the power for it is provided from a fused switched spur outlet in her bedroom. having switched off the power and removed the old light fitting i wanted to check the now exposed cable for functionality before fitting the new light so hooked up a multimeter between live and neutral, restored power and operated the switch - no power. removed fuse from front of switch - no fuse (no wonder it had not worked for some years). inserted new fuse switched on - flash, bang rcd tripped out. removed cable from switch thus isolating it completely. carried out continuity check end to end on all 3 cores - continuity confirmed. now for the perplexing bit - bear in mind cable is totally disconnected at both ends. at remote end of cable carried out resistance check betweem live and neutral - open circuit; between live and earth - open circuit; between neutral and earth - open circuit. repeated checks at other end of cable; live and neutral - 120 ohms; live and earth - 120 ohms; neutral and earth - 120 ohms.
the cable run disappears under the floorboards in the bedroom and i am going to have to trace it as soon as possible to find out what is going on. my daughter in law has no knowledge of when the fuse was removed and by whom.
any thoughts as to possible cause welcome as stated i am somewhat perplexed as to what could cause one end of a disconnected cable to read open circuit between live and neutral and the other end to read 120 ohms.