readings on a megger

[james king]

hi all can some one please tell me what the differance is on a short between any of the wires

e.g.

56.5Kohms
0.68ohms
>99Kohms

what is the closest reading a cable can take before a trips on a short circuit? i no what im trying to say but cant really explain it lol

 

[telectrix]

you've got me confused as well.

 

[james king]

lol haha right.......

if a have a reading of 89Kohms on my megger reading between live and earth this mean there is a short!!!! correct

sooooo

when u test r1+ r2 and u connect live and earth at CU the reading will ussalyy be 0. something.

soo at what point does the rcd detect a short circuit e.g. 50ohms???

 

[telectrix]

work it out. volts is 230v, the RCD needs 0.03A to trip, so use ohms law.

 

[Knobhead]

You’ve made over 200 posts on this board. But you can’t translate the basic readings a Megger is giving you.

I’m sorry but it just beggars belief.

 

[Dunc]

89,000ohms is not a short! 0ohms is! As Tel says apply ohms law, if you have a resistance between L and E of 89k then the current flowing to earth in a 230V circuit will be 0.0026A. That's never going to take out a MCB let alone a 30mA (0.03A) RCD.

 

[Dunc]

Also you're talking at cross purposes. R1+R2 readings are continuity tests carried out at very low voltages and will give the resistance of a circuit from end to end. Shorts in a circuit are tested for using an insulation resistance test. The applied test voltage is much higher (500V) and will give you a reading in Mohms. 1Mohm = 1,000,000ohms or 1000Kohms which is considerably greater then the resistances you will get with a continuity test.