measuring low voltage cable insulation
measuring low voltage cable insulation
(OP)
I have a problem on site , which is lasting for 4 days untill now and I did not figure out the cause or the problem .
the Situation is I had a short circuit and the main fuse broke down .
I checked Visual inspection for the contactor , overload , motor winding , cable and connections and i did not find the root cause , taking into consideration that I install a new fuse and start the motor and it is working now !!!!!
I still did not megger the cable yet ( check cable insulation) .
as i learned it is not so safe to megger the cable
Would you please help me with some steps to find the problem , and Also can u tell me how to measure the cable insulation in a safe way ????
the Situation is I had a short circuit and the main fuse broke down .
I checked Visual inspection for the contactor , overload , motor winding , cable and connections and i did not find the root cause , taking into consideration that I install a new fuse and start the motor and it is working now !!!!!
I still did not megger the cable yet ( check cable insulation) .
as i learned it is not so safe to megger the cable
Would you please help me with some steps to find the problem , and Also can u tell me how to measure the cable insulation in a safe way ????





RE: measuring low voltage cable insulation
RE: measuring low voltage cable insulation
Could the problem have been that the current through the fuse was too close to their rating?
RE: measuring low voltage cable insulation
I have a motor 75 kw and the Fuse is 160A
Another thing I id like to ask about .
this motor is starting by a star delta contactors , I cancelled the star circuit and let the motor works direct on line and it is working now for 4 days without a problem or short circuit .
Do u think that the problem is in the star control circuit ???
RE: measuring low voltage cable insulation
There could be other problems with starting the motor directly on the line. However, I will leave it to the motor experts to advise you about starting the motor directly on the line.
RE: measuring low voltage cable insulation
I'm Electrical engineer in the Midor Refinery firs of all u mentioned that it's not safe to meggar the cable and i don't know why it's not safe to meggar the cable ?!!!!
Secondly, i believe that ur motor is not protected by a ring type current transformer to discover the residual current occuring in the motor starting current as i believe that hi rating motors like yours which are mainly working as a low voltage motors will face the same problem as yours
witing for the reason of not meggaring the cable ?
RE: measuring low voltage cable insulation
Concerning meggaring the cable , I read this in some thread here as it may be danger to the other connected equipment to inject the cable with voltage , anyway it is just a precaution.
I believe that the current transformer is for step up/down current and not for protection .
please explain.
MY LAST DESICION IS TO USE A MECHANICAL INTERLOCK IN THE STAR DELTA CONTROL CIRCUIT .
RE: measuring low voltage cable insulation
Based on what you have described, it is fairly obvious the problem was with your starter or circuit. If the cable was the cause of the problem it would NOT go away.
In your original post you said it worked after replacing the fuse. Was the star starting circuit bypassed at this time too?
What does a current transformer have to do with anything? Maybe the poster who mentioned this is merely pointing out that he suggests a CT around the neutral or one around all three phases.