Odd PME discovery?

[Initforthemoney]

Hi guys,

Had an issue at a recent survey where doing a quick check and found we had pme with a reading of 0.44 ohms.

Called the network and they said they would send a guy around who promptly turned up and checked.

However his tester was giving a reading of 0.30!

I checked again using the same method he did and still got 0.44.

He said that he has found that some multi testers use the wrong range and we should be testing with a 20 ohm range and not 200 which apparently they are set at by default as otherwise it could be difficult to get a reading from a tt installation?

Anyone else had this?

I have dug out an old robin 4120dl that I used to use and that is still set at 20 ohm range from when I used to use it.

Might give that a hi in my place and compare but has anyone else had this?

 

[DefyG]

Discrepancy between meters? ........... all the time!

 

[Initforthemoney]

Discrepancy between meters? ........... all the time!

So how are we supposed to overcome this when it’s quite clearly a huge discrepancy?

Mine is an MFT1720 that was calibrated a couple of months ago and he was using a Megger Lt300

 

[nicebutdim]

Discrepancy between meters? ........... all the time!

and often with recently issued certificates of calibration. I'm not sure if supplied leads are tested or whether calibration takes place on meter only, but I've seen meters come back from calibration when I know for a fact the leads on the meter are dodgy.

 

[DPG]

and often with recently issued certificates of calibration. I'm not sure if supplied leads are tested or whether calibration takes place on meter only, but I've seen meters come back from calibration when I know for a fact the leads on the meter are dodgy.

I would expect only the meter to be calibrated.

 

[Initforthemoney]

Ok so just done a quick test on mine.

Megger mft on high gives 0.30
Robin 4120dl on 20ohm hives 0.22
Robin 4120 on 200ohm gives 0.28

Bearing in mind these readings are supposed to be what we should record and work to on installstions if we get a reading over max ze and yet on another tester it can be well below, what are we supposed to do?

This potentially screws up perfectly acceptable readings and modifications to circuits to bring them in line for no reason at all.

As far as the DNO are concerned their network is well within the max allowable.