Faulty Metrel MI 3125B or dangerous thumb!

[zap]

I have an MI 3125B. When testing for Zs at a socket I touched the test button with my thumb, the tester buzzed and displayed the 'dangerous voltage on PE' symbol. So I de-energized the system to look for the fault. There was no fault and insulation resistance at 500V DC was >999 MOhms.
I thought, strange, and proceeded with the Zs test again. I tried touching the button with other digits on both hands and it only alerted me to a fault when touching the button with my right thumb. I then asked a mate to touch the button and no alert so he pressed the button and the test result was very good. Why would this happen? Has anyone else experienced this?
I do have a calibration certificate for the metrel but not my thumb.
I'm awaiting for a response from Metrel.

 

[telectrix]

static? were you wearing pvc underpants?

 

[zap]

I did think of that. I used to be a bt engr. and when I worked on payphones I blew up just about everything I touched. I was then issued with anti-static mat, wrist band and low impedance cables etc. that solved the issue. Do you think San Miguel has anything to do with it, cos I had a few last night.

 

[james_t87]

Mine does that quite often.

 

[Des 56]

I do have a calibration certificate for the metrel but not my thumb. I like that line Zap

How old is the thumb ?

 

[james_t87]

Sorry didn't finish post. It does that quite often but corrects itself . It's to do with how well your connection between lead and terminal is

 

[zap]

I do have a calibration certificate for the metrel but not my thumb. I like that line Zap

How old is the thumb ?

58 this year. I suppose I should replace it:clap:

 

[zap]

Sorry didn't finish post. It does that quite often but corrects itself . It's to do with how well your connection between lead and terminal is

Thanks for that J. It was a new circuit with new crabtree accessories. I get the same result in the other socket, being a double. But I didn't experience it on other circuits.

Weird...

 

[MarkieSparkie]

It has been suggested in other threads that the test button on some Metrel MFTs can be over sensitive to static charge - registering it as a high touch voltage, as you have experienced, due to the high input impedance of the detector. Various solutions have been suggested, but when this occurs the most common solution is to retest pressing the button with a VDE insulated screwdriver. If the test results in another high touch voltage warning - investigate the cause as it might well be a valid fault, usually between N & E. However, if the retest produces a normal test result you can be fairly certain that static charge was the cause, in this case you should consider a change of safety footwear to the type with anti-static soles which will leak any accumulated charge safely.

 

[zap]

It has been suggested in other threads that the test button on some Metrel MFTs can be over sensitive to static charge - registering it as a high touch voltage, as you have experienced, due to the high input impedance of the detector. Various solutions have been suggested, but when this occurs the most common solution is to retest pressing the button with a VDE insulated screwdriver. If the test results in another high touch voltage warning - investigate the cause as it might well be a valid fault, usually between N & E. However, if the retest produces a normal test result you can be fairly certain that static charge was the cause, in this case you should consider a change of safety footwear to the type with anti-static soles which will leak any accumulated charge safely.

Thanks Mark,
I had a response from Metrel support who haven't heard of this phenonemon. They suggested static was probably the cause as the tester uses 40V AC and static is likely to be much higher. They also enquired about my carpets which could also be contributing to the anomaly. However, that particular test was in the loft where there are no carpets.
I take your point about footwear cos I was at home and was still in my slippers whilst conducting some tests!
I'll see if it's repeatable with my slippers on and then don my work boots and see if it's repeatable and post the result back here.

 

[zap]

Okay, I've repeated the Zs test with slippers then with work boots on and the results were the same.
I did manage to get all fingers and thumbs to cause the alert which removes that anomaly.
A little more experimentation revealed the following:
If I hold the instrument in both hands I get the alert.
If I hold the instrument in one hand I do not get the alert, even if I use a digit on the other hand to touch the button.
James_t87, I'd be interested if you could try this out and see if it's holding the instrument in both hands that's causing the issue. If so, I'll get back to Metrel Support and let them know.

 

[power ranger]

Hi Zap

I have never used any metrel stuff as Im a fluke fanatic! But have you done your dead tests to confirm earth continuity?

 

[zap]

Hi Zap

I have never used any metrel stuff as Im a fluke fanatic! But have you done your dead tests to confirm earth continuity?

Yep, measured, and they look okay to me

r1 = 0.24
rn = 0.24
r2 = 0.43
R1+R2 = 0.15
Zs = 0.64

 

[44ALLAN]

I would try changing your name 1st.................just asking for trouble with that one mate