Insulation Testing Query

[Jonny72]

Quick question. I am new to electrical installation so please be patient. You guys are great at answers. Re Insulation Testing. Why if I test using 250vdc to a get a lower reading of 105meg but infinity at 500vdc. Ring circuit and everything disconnected (I hope ). Also meter warna of 40v for a few seconds after the test. Is this a capacitive effect??

Jonny

 

[timhoward]

My first thought is that I'd actually be a bit suspicious of the meter and whether it is working properly at 500v.
Is this a calibrated meter that you trust? Have you tried it with a Cal Card (fairly cheap) or Checkbox?
(I ask because that is an unusual situation, there are a couple of reasons you can get a lower reading at 500v.)

 

[timhoward]

Have you tried a 500v test with the leads clipped to each other?
Which tester is it?

 

[Jonny72]

My first thought is that I'd actually be a bit suspicious of the meter and whether it is working properly at 500v.
Is this a calibrated meter that you trust? Have you tried it with a Cal Card (fairly cheap) or Checkbox?
(I ask because that is an unusual situation, there are a couple of reasons you can get a lower reading at 500v.)

Not it's calibrated 6 months ago. It's a wee DiLog and hasn't let me down yet. I know I would have expected more accurate reading at 500v.

 

[Jonny72]

Have you tried a 500v test with the leads clipped to each other?
Which tester is it?

Yes I always test with leads apart and the leads connected and was fine. It's just a wee DiLog. I am only starting in the trade so best I can afford at moment.

 

[Jonny72]

My first thought is that I'd actually be a bit suspicious of the meter and whether it is working properly at 500v.
Is this a calibrated meter that you trust? Have you tried it with a Cal Card (fairly cheap) or Checkbox?
(I ask because that is an unusual situation, there are a couple of reasons you can get a lower reading at 500v.)

Just ordered a calcard form Amazon so will give that a go. Can you get MFTs fixed if an issue??

 

[pc1966]

I have to agree, getting lower at 500V compared to 250V is very suspicious!

Usually it is very much the other way if SPD fitted somewhere (tens Meg or more at 250V, under Meg at 500V), and you can see IR rise with test time as dielectric absorption plays out, but rising a lot going up in voltage looks like a fault.

 

[timhoward]

Yes I always test with leads apart and the leads connected and was fine. It's just a wee DiLog. I am only starting in the trade so best I can afford at moment.

Nothing wrong with a DiLog. A mate has had one for years and it does the job. It's good you've ordered a CalCard.

Is it a 9083P? If so I have a slighly quirky theory....

The specs on those are a little confusing, the Display Range for IR is <200M but the highest measuring range is 20M to 100M according to the manual.

One reading of the above could be that the 250v test was within 100M +5% so it showed the value, and the 500v test warmed things up a little and things improved and it went off the scale....

A CalCard is the way forwards.

 

[buzzlightyear]

On most testers now mosley the diglog
When testing it will show pass or fail
If its in calabration should be OK.
Some time you should try and get hold of a check box and call card. So now again
You can see if you are within tolerance.

 

[Jonny72]

Nothing wrong with a DiLog. A mate has had one for years and it does the job. It's good you've ordered a CalCard.

Is it a 9083P? If so I have a slighly quirky theory....

The specs on those are a little confusing, the Display Range for IR is <200M but the highest measuring range is 20M to 100M according to the manual.
View attachment 113147

One reading of the above could be that the 250v test was within 100M +5% so it showed the value, and the 500v test warmed things up a little and things improved and it went off the scale....

A CalCard is the way forwards.

I like that theory. I did the testing dampish sort of day so that actually makes sense (always damp in Northern Ireland). The 500v possibly drier out connecters. To be honest it is the most basic, simple but reliable wee machine but does everything I need as a domestic installer. Thanks for heads up on that card. Should be here on Thurs. Cheers, Jonny

 

[Jonny72]

Nothing wrong with a DiLog. A mate has had one for years and it does the job. It's good you've ordered a CalCard.

Is it a 9083P? If so I have a slighly quirky theory....

The specs on those are a little confusing, the Display Range for IR is <200M but the highest measuring range is 20M to 100M according to the manual.
View attachment 113147

One reading of the above could be that the 250v test was within 100M +5% so it showed the value, and the 500v test warmed things up a little and things improved and it went off the scale....

A CalCard is the way forwards.

Mate I cancelled the card but got hands on some 0.20 ohm and 20Mohm resistors for 1 quid. I quickly soldered onto a board and have my own Cardcard with 0.2, 0.4, 0.8,, 20M, 100M and 200M tests. And it works. also Dialog machine doing fine. Yes 10 mins work but saves .e 20 quid. Just a cheap skate really

 

[timhoward]

Mate I cancelled the card but got hands on some 0.20 ohm and 20Mohm resistors for 1 quid. I quickly soldered onto a board and have my own Cardcard with 0.2, 0.4, 0.8,, 20M, 100M and 200M tests. And it works. also Dialog machine doing fine. Yes 10 mins work but saves .e 20 quid. Just a cheap skate really

It sounds as though we are similar.... here is my DIY EV tester in use today....! Total of £38 spent. (I did have a proper one but it is still nowhere to be found)

 

[Jonny72]

It sounds as though we are similar.... here is my DIY EV tester in use today....! Total of £38 spent. (I did have a proper one but it is still nowhere to be found)
View attachment 113266

Tim - shear brilliance mate