Short circuit and break up cable on fault finding rig

[Lee Gold]

Can someone explain a short circuit And a break in a cable when fault finding please what is the meaning of them please. Was fault finding today on test rig

 

[Richard Burns]

A short circuit is a direct contact ("fault of negligible impedance") between line and neutral or in three phase between line and line or line and neutral.

If you measured the resistance, with a low resistance ohmmeter, between the two conductors with a short circuit you would expect to see resistance levels much less than 1Ω.

If there is a conductor that is meant to be continuous and there is a break in the cable then the resistance from end to end of the cable, when measured with a low resistance ohmmeter would read full scale deflection (overlimit, >2000Ω, O/L, etc).
Normally a cable will show a low but measurable resistance.

 

[Lee Gold]

A short circuit is a direct contact ("fault of negligible impedance") between line and neutral or in three phase between line and line or line and neutral.

If you measured the resistance, with a low resistance ohmmeter, between the two conductors with a short circuit you would expect to see resistance levels much less than 1Ω.

If there is a conductor that is meant to be continuous and there is a break in the cable then the resistance from end to end of the cable, when measured with a low resistance ohmmeter would read full scale deflection (overlimit, >2000Ω, O/L, etc).
Normally a cable will show a low but measurable resistance.

Thanks mate

 

[telectrix]

lee, just get some scrap cable/wire and a multimeter. have a play. see what happens when you cut cable or short it out.

 

[Lee Gold]

I'm going to mate I've got a multimeter but It's abit crap but il do it today mate cheers

 

[hightower]

lee, just get some scrap cable/wire and a multimeter. have a play. see what happens when you cut cable or short it out.

I was tinkering at the weekend with an Insulation Resistance tester and a length of 4mm T+E. Pretty much had to cut through the lot and then squeeze it with pliers to get the IR tester to show a fault. Granted it was only a 1m length of 4mm, and a 100m length will probably show up a fault earlier, but still, I was expecting the insulation resistance to drop well before it did. Very interesting.