External Earth fault loop impedance concern

[robbieforrest]

I do not have a lot of Testing experiance,but i have just passed my 2392 10 in domestic testing.
My question is that i was testing a new CCU today and could not get a Ze reading at the origin, and also could not get the PEFC reading, it came up with err, I was using a megger mft1153 tester, any ideas

[Central Scrutinizer]

dont sell your self short - 2392-10 is about intitial verification, and is equally valid for commercial/industrial installations as it is for domestic.......

what sort of supply do you have?

did you carry out the test correctly, i.e main earth disconnected for Ze, and reconnected for PEFC? where you on 'no trip loop' (three leads) or 'high' on 2 leads?

Even if your main earth was open circuit (or simply non exisitant) the you should still obtain some PEFC reading through your extraneous services

i have both meggers and ***kes, and one of the primary reasons i prefer the ***ke is becuase it gives a loop impedennce reading and a fault current reading at the same time, and that could give a better indication to the problem than the megger

[robbieforrest]

I had the main earth disconnected and was using the2 lead method, and then reconnected it to the met to do the PEFC. I was on the no trip loop test setting. The supply was a TN-C-S. I have another board today to test so I should find out if my Megger is okay, I have only had it a week. Thanks for the reply.

[robbieforrest]

Thanks for the replies i have resolved the issue, it was a school boy error, it is a 3 lead test on no trip loop not a 2 lead test.

[Central Scrutinizer]

haha, everydays a school day!

and of course your second second schoolboy error, unless you had an RCD before the board, you should have been doing the test on high loop, no trip is for RCD protected circuits

as a guide with the megger, it 'does what it says on the tin'

if you select 'no trip loop' turn the meter on its end and you will see a black hole with 'no trip loop' written on it - stick your black lead in there (for the neutral), and the rest follws, so you have to use three leads

if you havent selected 'no trip loop' and you turn the meter on its end and you have a lead in the black hole wot says 'no trip loop' then.....erm.....you have it wrong!

i have saying, 'believe what your meter is telling what you to do, it generally knows FAR more than you do'

hahahaha

[robbieforrest]

thanks for the advice, i am much wiser today.