insulation resistance test ?

[rapidrich]

i tryed doing a insulation resistance test but the metter reading comes out at 0.00 even if i clip the test leads together and press test still reads 0.00 is the tester nakerd?

 

[Mr Mark Sparks]

it will be 0.0 with leads together
it should be >200 or 299 500 999 depending or your meter with leads open

 

[rapidrich]

yes my tester is over 299 (ol) it does read that with leads open ? how come it reads 0.00 when performing the test ?

 

[markythesparky]

You have a short!

I presume that you are testing Live to Neutral. if this is correct you have 'stuff' plugged in or connected to the circuit still. hope you havent used 500v as you may have blown them up!!

if this is on live to earth you have a fault and i would be surprised if you could even turn this circuit back on.

If this is neutral to earth, check that the mains switch is off as the neutral and earth are linked back at the substation.

Regards
Markythesparky

 

[rapidrich]

i added a spur socket to a ring i had everythink unplugged and swiches turned off

 

[markythesparky]

what cables are you testing between?

 

[rapidrich]

tryed phase/neutral and phase/earth

 

[markythesparky]

Ok, firstly if its phase neutral then you definately have somehting on the circuit that you havent seen yet. especially if you can still turn the circuit on. if there was nothing on the circuit and your meter still shows a dead short you would get an almighty bang when you turned it on. no two ways about it.

secondly, if you are testing between phase and earth, you need to make sure that the main switch is double pole and turned off. turning the MCB of is not enough as it does not disconnect the neutral. otherwise youll get the reading through whatever is plugged in down the neutral to the substation and back up through the earth therefore giving a phase to earth short. if you have this reading other than with the reasons above you will definately experience a bang when turning it on.

It cannot be anything else.

 

[NoSparks]

I now always do a continuiety test (ie low resistance test) between live and earth befor starting the insulation test. If the result is > 1999ohms then I proceed to 100v. If that gives 0.00MOhms then as said above there is something connected. Two weeks ago it took 3/4 hr to find all items and disconnect them. The final offending items was a tooth brush charger! Why all these items have low resistance to earth I have yet to discover.

 

[coxy]

Hi I recently tested a job before I started a kitchen because I had to put a rcd on the circuit, i thought i had disconnected everything and done line & n together to earth - but reading was 0.25ohms !!
Eventually found the burgular alarm was on the circuit !! - disconnected and was ok !!