IR Testing Minor Works

[soulman]

Had a problem on a circuit twice in one week, 1st one movement of lighting pendant, IR tested L-N connected together to E 500v = 0.40Mohms, linked out all dimmers still 0.4Mohms eventually traced it to a transformer in one of the lights, removed it. IR now >200Mohms. I had exactly the same result while IR testing a socket circuit to add an extra socket. It turned out to be a mobile phone charger plugged in inside a wardrobe. My question is, why was getting a reading like that when L-N were connected together to earth. It seemed a bit extreme for me to remove a metalic light fitting, just to perform a minor works. Am i missing something here? What would you guys have done if you got a reading like that.

Cheers

When doing any minor works even like for like changes i always check the gas & water are bonded first, R1+R2 to the point where i am extending or fitting a new accessory, then IR test the circuit, i also test the rcd before works commence. I do a ELIT on completion. The electrician i trained with, never ever checked the gas & water was bonded or any dead tests. he just done an ELIT and tested the rcd. I always like to do things properly, after a while i find it just becomes habit.

 

[Evans Electric]

The Neutral is connected to earth on the supply side Soulman .

 

[soulman]

All conductors were removed from neutral and earth terminals

Cheers

 

[Evans Electric]

I don't know then , borrowed neutral still in the Neutral bar ?

Did this Transformer have an earth ? The reading is was getting back to the earth somewhere and it must have been to do with the transformer .

Any Fluoro,s in the circuit ?

 

[Steve3948]

Well the mobile phone charger would have been class 2 - no earth ?

 

[sellers]

I'm 99% certain a minor works only asks for the insulation resistance on any new or modified wiring, not the entire circuit. While I do test the entire circuit I am sure you can test only your additions and record those results, which would come in handy when you come across those houses of horrors.

 

[soulman]

Sellers i was always taught that you should be checking the IR of the circuit you are connecting your work to ensure it is safe & complied with the regs.

 

[professional]

Correct - you must test the circuit that you are adding to - to ensure that it is safe to do so.

This is part of the initial verification process that is widely ignored.

 

[soulman]

I believe it is ignored on a minor works, because i have asked a few sparks that i know, they have all said the same thing, if they get a low reading they reduce the voltage to 250v sometimes. most of the time they dont bother testing IR as it wastes time looking for whatever could be bringing the IR down when all your there to do is install and extra light or socket. So i want to see what you guys do.

 

[Phoenix]

Consider possibly doing an IR before you start work, and then if you find its already down, then limit the IR to the your new work only and make a note that the existing is reading down.

The lighting transformer shouldn't be dragging it down on a poles to earth test, unless its a) faulty, or B) somehow connected live-earth through wiring being reversed somewhere.

I always test at 250v before going to 500v, you never know what some muppet had hung between live and earth.... actually I normally start of on continuity or K-ohms range, if its solidly down or in the K-ohms range then waste of time meggering it.

There isn't much stuff which will affect a poles to earth IR test.... Surge protectors, RCBOs with F/E flylead, some RCD sockets and spurs. The vast majority of stuff that has stuff connected to earth consists of filters which are generally capacitive in nature, which means the needle will gradually creep up as the capactance charges up.

 

[springcrocus]

I believe it is ignored on a minor works, because i have asked a few sparks that i know, they have all said the same thing, if they get a low reading they reduce the voltage to 250v sometimes. most of the time they dont bother testing IR as it wastes time looking for whatever could be bringing the IR down when all your there to do is install and extra light or socket. So i want to see what you guys do.

Sorry, but this is just lazyness. X(

 

[Zeespark]

They wont say it wastes time when the RCD keeps tripping at a low IR and they cant sign the certificate off as they havent tested IR at 500V.

AndyGuinness