nivag
-
hello.
just wondered if any of you have experienced this or can possibly shed some light on it.
today i went to a fault on an immersion circuit
symptons was -
upon waking up, customer noticed B16 MCB had tripped along with 1 of the split load 30ma RCDs. he reset RCD which stayed on and when he tried to reset the MCB it blew straight off again (the RCD held however)
he left it for a day and at some point the RCD had triped off again but he managed to reset it.
arrived at job with just MCB off
upon initial investigation, the load side from the Double pole switch in loft next to the cyclinder was all clear, it was just feeding the element which tested out fine. i then started to investigate the circuit between the CU and the D/P switch to which i found some serious burning of the cable, and once i opened up the switch i found some burning in there too.
the terminals of the switch were all tight and it looked to be the earth link that links the terminal screws on the cover plate that had been the source of heat, the burn of the cable also looked to be from the earth.
this is where it gets odd.
the burn to the cable was only for about a meter, and it wasnt directly next to the d/p switch either, it had a meter or so between of good cable seperating them, then the cable all the way back to the CU was ok too,
why would this be the only 2 sources of heat damage? possibly weak terminations to the link of the cover plate? and there was a very tiny corner of the duvet leaning on the cable at the point of burn so i guess this could have derated the cable CCC?
then the question is why would the earth heat up when there was no fault being inicated upon dead tests. and that is presuming the RCD was opperational and would have disconnected within the required time thus not allowing the cable to heat up to such a tempreture.
obviously it had to be repaired so with the MCB AND the corresponding sides RCD isolated, i snipped through the cable. at that very moment, the lights in the loft dimmed to at bout 25% left.
you could think possibly the lights was borrowing and earth for the neurtal path back but the RCD (presuming it was working) wouldnt have even held, and i arrived at the job with all lights fine. also, there was nothing upstream - just a meter of T&E and a disconected Double pole switch.
the other side of the split load board was totally un effected and this is the side the lights were fed from.
voltage had dropped to 151 volts
with the Mainswitch isolated, the incomming was still 150Volts.
turn the main switch and some crcuits back on and the more load the lower the voltage - got down to 30v supply.
not enough for my meter to let me carry out any live tests.
RCD test buttons opperated them at 150v but not down at 30v
it was TNS system on Econ 7
also, would a drop in voltage stop a MCB from opperating?
any ideas would be nice
thanks in advance.
just wondered if any of you have experienced this or can possibly shed some light on it.
today i went to a fault on an immersion circuit
symptons was -
upon waking up, customer noticed B16 MCB had tripped along with 1 of the split load 30ma RCDs. he reset RCD which stayed on and when he tried to reset the MCB it blew straight off again (the RCD held however)
he left it for a day and at some point the RCD had triped off again but he managed to reset it.
arrived at job with just MCB off
upon initial investigation, the load side from the Double pole switch in loft next to the cyclinder was all clear, it was just feeding the element which tested out fine. i then started to investigate the circuit between the CU and the D/P switch to which i found some serious burning of the cable, and once i opened up the switch i found some burning in there too.
the terminals of the switch were all tight and it looked to be the earth link that links the terminal screws on the cover plate that had been the source of heat, the burn of the cable also looked to be from the earth.
this is where it gets odd.
the burn to the cable was only for about a meter, and it wasnt directly next to the d/p switch either, it had a meter or so between of good cable seperating them, then the cable all the way back to the CU was ok too,
why would this be the only 2 sources of heat damage? possibly weak terminations to the link of the cover plate? and there was a very tiny corner of the duvet leaning on the cable at the point of burn so i guess this could have derated the cable CCC?
then the question is why would the earth heat up when there was no fault being inicated upon dead tests. and that is presuming the RCD was opperational and would have disconnected within the required time thus not allowing the cable to heat up to such a tempreture.
obviously it had to be repaired so with the MCB AND the corresponding sides RCD isolated, i snipped through the cable. at that very moment, the lights in the loft dimmed to at bout 25% left.
you could think possibly the lights was borrowing and earth for the neurtal path back but the RCD (presuming it was working) wouldnt have even held, and i arrived at the job with all lights fine. also, there was nothing upstream - just a meter of T&E and a disconected Double pole switch.
the other side of the split load board was totally un effected and this is the side the lights were fed from.
voltage had dropped to 151 volts
with the Mainswitch isolated, the incomming was still 150Volts.
turn the main switch and some crcuits back on and the more load the lower the voltage - got down to 30v supply.
not enough for my meter to let me carry out any live tests.
RCD test buttons opperated them at 150v but not down at 30v
it was TNS system on Econ 7
also, would a drop in voltage stop a MCB from opperating?
any ideas would be nice
thanks in advance.
