megger strange test readings... help!!

bororich · Jan 20, 2010

hi guys...
i have been testing lately and have found my megger 1553 has been giving me higher r1+r2 results than the Zs results... i use the same leads, always use good batteries and have it calibrated? is the machine at fault? has anyone ever had similar experiances? im aware that there maybe parralell earths aswell but it is happening too often to be that...

please help!

Darkwood · Jan 20, 2010

Check you not getting confused by parallel earth path like metal conduit, armour, trunking or metal building structure if linked to the back of a metal box?

bororich · Jan 20, 2010

yeah i have checked this there is no parallel earth path on this circuit i did today.... twin and earth cable into a plasterboard box.. it has really confused me? mates at work are stumped too!!

Darkwood · Jan 20, 2010

Its probably just a poor connection only showing up when you do the ohms test off the battery in your meter, as the mains voltage 200 plus volts more than the battery test and is not showing this problem.
The cables are all probably in and screwed bit one probably needs tweaking tighter.

ChristianG · Jan 20, 2010

check your leads?

bororich · Jan 21, 2010

i will replace the leads and get back to you.. they seem fine visually but i will swap them for another set. thank you for the advice

Sintra · Jan 21, 2010

Check your meter on a known resistance like a check box.

Eggster71 · Jan 21, 2010

Had similar with my CM500. Was the leads!!

Megger TSG · Jan 22, 2010

Hi

You have stated you have changed the batteries, so after checking the test leads it is possible the unit may have a fault.
Have you noticed any difference in readings between the mains test lead and the 3 individual leads?

Regards

Megger TSG

donm · Jan 22, 2010

mine does the same on no trip but ok on high i think it uses the neutral on no trip as the other day i had a skt with no earth on high it came up 55v well no response when i put it on no trip it took a reading