Megger 1533 showing phantom voltages on Ir and Impedance

[miloharrisson]

Hi!

Some help would be appreciated!

I've just moved into new house, wanting to check insulation resestance etc as getting some nuisance tripping, this bits not important.

Got my megger out, which has worked perfectly up until now, it doesnt have a test cert, but I'm not fully qualified and guy I work with uses his for certification, but the readings have always been the same... Anyway, went to IR test and i'm getting random voltages and the megger alarms going off on either high or low range resistance settings. Screens showning between 110 and 80V whether leads are connected to anything or not. I changed the batteries assuming this might be the issue, same with brand new batteries. I took it out of the kitchen in case it was somehow picking up interferance from induction hob (which would be impossible as whole board was isolated, clutching at straws) or the smart meter, (again, straws).

Not really sure where to go from here, I missed my local CEF calibration day as I was mid move, I winder if anyone else has had similar happen??

All help much appreciated.

Thanks

 

[buzzlightyear]

Megger will show phantom voltages (vol) if you are testing near a source, a few years back a had the same, I had a megger 1720,not showing on the information . I rang up megger told them, oh it must be a phantom voltages.

 

[timhoward]

I've discussed this with the OP directly as we are friends, but for anyone searching in the future, the service manual suggests that this behaviour will be seen if FS1 or FS2 on the relay board has blown.

"Correct voltage measurement relies on the 1A fuse (FS2, relay board sheet 1) being intact, so it is necessary to perform
regular fuse checks. Normally the Earth terminal of the instrument is tied to 0V(A) through this fuse and through resistors
R111 & R114 in the ohms reference circuit (measurement board sheet 2). If the 1A is blown and voltage is being measured,
then the potential on the instrument Earth terminal will rise.
Note: To assist in fault-finding in the event of a fuse problem, diode D45 (measurement board) can be fitted temporarily.
This tells the MFT to bypass all fuse checks.
"

The alarm he mentions is consistent with this too:

So first step is opening up and checking all four fuses on the relay board.