confused about IR reading

[zone77]

when doing a IR test, sometimes a reading starts climbing up and doesnt stop. Is there something on a circuit that causes this or is my tester playing up? if this is normal what reading do i record?

 

[Mark.W]

What tester are you using? Most testers have a second beep, which is where you release the test button and record the reading.
I read somewhere that the reason the values keep climbing is because of inductance in the conductor, when you do IR testing you are actually forcing a voltage down the conductor,something like that anyway. I'm sure someone with more knowledge will elaborate more.

Mark

 

[zone77]

my tester is a robin KTS 1610.

 

[Mark.W]

Does it beep when you press test and then beep again after a few seconds?

 

[zone77]

cant say ive noticed but will try it to see

no doesnt beep. it has a test button that locks on and 98% of the time gives a steady reading.

 

[NoSparks]

Practically any electronics on the circuit will cause this. Look for items which have not been disconnected such as GU10 light bulbs, toothbrush chargers etc. Very often the resistance will oscilate over a large range of values. If the minimum values is within acceptable limits (which it often is) then record it as a pass.

If your meter just keeps going up to 199 then the cable resistance cannot be less than 199 so record it as such.

In passing I always test at 100v first then 240v and only if all is OK do I progress to 500v. The reason. Well once there was a permanently conected fairly expensive projecter connected to the circuit with a very obscure FCU (we found it 2 weeks later) I tested at 500v and wrote off the projector, Once bitten...

 

[monkeyelectric]

I got a fluke 1652 and sometimes it does the same, in particular on older cable, probably just some moisture in the cable causing resistance against the charge building, thats what i've always thought it to be anyway

 

[kung]

Try batteries might be low

 

[zupos40]

when doing a IR test, sometimes a reading starts climbing up and doesnt stop. Is there something on a circuit that causes this or is my tester playing up? if this is normal what reading do i record?

I get it regularly on old wiring plus when testing MICC.

MICC is because your IR tester is charging up the cable, once the value reachs 199 Mohms, I stop leave leads and meter connected to safely discharge (it will not do any harm to your meter)

In the case of old cables it generally a combination of age (harding of conductor insulation due to overhating etc) and dampness, moisture, VIR and old flexible conductors at lighting outlets regular occurance, inductance and cable capacitence have very little effect on PVC twin and earth, it does have some effect on armoured and large csa PVC single in trunking.

I had examples where the reading starts high and goes down usually cable over 30 years old and no there was not any item connected to the cable.

I tested ring final where wall has damp problem, this can cause same problems.

finally as other have posted could have equipment connected that is being chargerd up by IR tester, it alway worth testing at 250V first even thou you are not complying with regulation incase you not sure that every current/ voltage sensitive equipment etc has been disconnected.