Insulation Resistance Test??

[Kev2632]

Hello,

im reading up on the insulation resistance test at the moment, when doing an insulation test on say a ringmain, and there is switched fused switches with neon, and the switch is OFF, can this still affect the reading? also when doing the L to N, why is it sometimes get really low reading of 0.01ohms, when everything is unplugged?. whats the reason for that?

Thanks.

 

[Specialist]

The Neon should'nt have any effect as long as the Spur is off, the Neon is fitted across the load side to show when it's turned on.

An 0.01R reading on an Insulation test is a S/C it could be caused by wires not correctly terminated & touching etc.

 

[Marvo]

I'm not sure about the switched fused units you have but I've come across those 5 into 1 plug banks where the neons are wired between the live and earth.

The thing with neons in circuit is that if they're between live and earth they'll actually illuminate during the IR test so they're easy to spot.

 

[Specialist]

Hi Marvo: A switched fused spur is a Switch with an inbuilt fusehoder, used over here on the supply to such things as Burglar Alarms, Heating systems etc.

 

[Flying Ninja]

L-N Reading of 0.01 usually means you have missed an outlet. I find it in kitchens where sockets are in cupboards and often miss the Hob ignition and extract. For this reason I usually test at 230v first so as not to damage any equipment

 

[Specialist]

L-N Reading of 0.01 usually means you have missed an outlet. I find it in kitchens where sockets are in cupboards and often miss the Hob ignition and extract.

Thanks mate: I forgot about that, for some reason I thought he was talking about new cct's. Oh well they say old age don't come alone lol.

 

[GLENNSPARK]

and the obvious one of course.....connected loads such as showers etc......these will give off fake readings.....

 

[Kev2632]

yea but why would a shower or that affect the ring main that is being tested at the moment?

 

[telectrix]

Hi Marvo: A switched fused spur is a Switch with an inbuilt fusehoder, used over here on the supply to such things as Burglar Alarms, Heating systems etc.

sorry to be picky, but alarm systems use an unswitched FCU

 

[SPARTYKUS]

yea but why would a shower or that affect the ring main that is being tested at the moment?

....you'd be suprised!! Seen a few showers off a radial socket circuit!

 

[Mark_Burgess]

Plug in air freshener hiding somewhere!

 

[telectrix]

could even be a cooker hood with it's plug and socket inside the chimney.

 

[Kev2632]

....you'd be suprised!! Seen a few showers off a radial socket circuit!

can other circuits affect the Ringmain being tested on that RCD?

 

[Specialist]

Do you think that Glenn possibly missed the bit about the RFC ? Have you turned off all sockets / spurs ? & checked for hidden sockets / spurs behind units in the kitchen ? Kitchen fitters have a habit of doing this. Also check in the airing cupboard if there is 1 to make sure the immersion is not tapped off the ring or as 1 i found today the central heating wiring chopped into the ring & taken into a landing cupboard.

 

[Mark_Burgess]

sorry to be picky, but alarm systems use an unswitched FCU

That is the normal way.....
One local company around here (actually just stopped trading) I had a big time argument about segregation of safety circuits, as they would not accept it exists, until the BRB came out.

 

[Kev2632]

Do you think that Glenn possibly missed the bit about the RFC ? Have you turned off all sockets / spurs ? & checked for hidden sockets / spurs behind units in the kitchen ? Kitchen fitters have a habit of doing this. Also check in the airing cupboard if there is 1 to make sure the immersion is not tapped off the ring or as 1 i found today the central heating wiring chopped into the ring & taken into a landing cupboard.

yea checked everywhere!!, there was no other appliances plugged in at all, would other circuits on the rcd affect the ringmain that is being tested?

 

[Specialist]

sorry to be picky, but alarm systems use an unswitched FCU

You've obviously led a sheltered life mate, Alarm systems are supposed to use an Unswitched fused spur. Unfortunately a lot of Installers don't know the difference & fit Switched. I used to carry 20 unswitched on the van with me we were changing so many of them after subbies.

 

[Specialist]

yea checked everywhere!!, there was no other appliances plugged in at all, would other circuits on the rcd affect the ringmain that is being tested?

Did you disconnect the RFC conductors at the CU & check ?

 

[morph]

what regs says you need a unswitched fused unit for an alarm ?

 

[morph]

ps
a spur is not a piece of equipment or electrical assessory

 

[Kev2632]

Did you disconnect the RFC conductors at the CU & check ?

nope, dont normal have too, but can anybody answer this one" if you are testing at the Consumer on the 1 side of the RCD, and everything is isolated are you are doing L-N on the ringmain, will other circuits on that RCD affect the result of the circuit being tested????

 

[Specialist]

nope, dont normal have too, but can anybody answer this one" if you are testing at the Consumer on the 1 side of the RCD, and everything is isolated are you are doing L-N on the ringmain, will other circuits on that RCD affect the result of the circuit being tested????[/

If you find what you think is a fault on an insulation test of any circuit then the first thing to do is completely isolate it from the board & test again.

 

[Kev2632]

nope, dont normal have too, but can anybody answer this one" if you are testing at the Consumer on the 1 side of the RCD, and everything is isolated are you are doing L-N on the ringmain, will other circuits on that RCD affect the result of the circuit being tested????[/

If you find what you think is a fault on an insulation test of any circuit then the first thing to do is completely isolate it from the board & test again.

Thanks for that, but if you are testing at the Consumer on the 1 side of the RCD, and everything is isolated are you are doing L-N on the ringmain, will other circuits on that RCD affect the result of the circuit being tested???

 

[Flying Ninja]

As posted before, Remove all cables from CU if you are getting these sort of readings and re test. Other circuits may have an effect as the neutral and earth will be linked as you are only isolating the line between circuits.

 

[Mark_Burgess]

Thanks for that, but if you are testing at the Consumer on the 1 side of the RCD, and everything is isolated are you are doing L-N on the ringmain, will other circuits on that RCD affect the result of the circuit being tested???

I see what you are saying, and as long as all other MCB's, RCD's and the isolator switch are open.

However, is there only the one ring circuit?
I think you have to disconnect and confirm continuity as someone may have done a mix up of cables in the consumer unit.

 

[Kev2632]

As posted before, Remove all cables from CU if you are getting these sort of readings and re test. Other circuits may have an effect as the neutral and earth will be linked as you are only isolating the line between circuits.

Yea thats very true, doesnt some switches like 13amp switches fused, cooker switches, shower switches always isolate the neutral as well?

 

[Kev2632]

I see what you are saying, and as long as all other MCB's, RCD's and the isolator switch are open.

However, is there only the one ring circuit?
I think you have to disconnect and confirm continuity as someone may have done a mix up of cables in the consumer unit.

Yea just 1 ringmain doing the whole house, but when you disconnect the circuit and checking for continuity are you meaning just Ring Continuity aye?

 

[Mark_Burgess]

Yes, to make sure that is the ring and not mixed with another ring or spur by some previous meddler.

 

[Kev2632]

Yes, to make sure that is the ring and not mixed with another ring or spur by some previous meddler.

Yea thats very true, it just had my head scratching today, because ive never really had such a low reading on L-N before, but it seems common

 

[Flying Ninja]

Yea thats very true, doesnt some switches like 13amp switches fused, cooker switches, shower switches always isolate the neutral as well?

Yes, They are double pole switches.