Zs & Megger MT1552 Tripping

[Big Man]

Can anyone help...

I'm trying to get the Zs reading on a radial lighting circuit but my Megger MT1552 keeps tripping (TRP) during the test.

I'm: Performing a Live test Main switch, RCD and MCB Closed

and performing the test at various points on the circuit including the furthest point using the 3 lead test method set to the 'no trip' loop impedence setting results in the Megger tripping. I've also tried only using two leads with the same result and also the normal loop impedence test resulting in the RCD tripping as expected.

Incidentally I tested the Zs of a ring circuit using the socket attachment without problems and with results matching calculations.

Any help would be appreciated as to why my Megger is tripping.


Thanks

 

[sparkswillfly]

take your ze and add your r1+r2

 

[Big Man]

I understand the calculation concept but you shouldnt just use the calculated method alone. It should be substantiated with a measurment from the EFLI tester.

Any ideas for why it's tripping???

 

[sparkswillfly]

yes i should imagine its because the tester put a fault current in the fault loop over about 10 amps and i assume your on a 6 amp breaker

 

[plantpot]

If it is a B type breaker it will do it 9 out of 10 times (i have given up trying) as others say do calc .if you

really want to do test put a D type in and test then put B type back in,this seems a bit of a waste of

time to me though as if you have done ZE and r1 and r2 you have already done main tests.

If you are worryed there is nothing wrong with your tester.

 

[Spudnik]

As above really.

You will probably find that swapping the MCB for even a B16 or similar may also help.

just make sure to swap it back to the 6 when done.

 

[Big Man]

Forgot to mention I'm using a 10A MCB Type B for lighting due to load and the property's original wiring.

Thanks for all your suggestions already. Any more will be very welcome.

I'd just like to say that this site is really useful.

Thanks electricians forum... and members

 

[plantpot]

I once said swap to to 16a to test and swap back to 6a in a testing course .

The instructor looked at me as though i had slept with his wife and said no way.

we live in the real world though

 

[mikeymoo]

Hi Big Man. If your not already use the clips to take the reading not the probes. And yes its a 3 lead test on no trip for the megger. The smallest of movement with the probes will trip the RCD.

 

[Big Man]

Good advice, thanks I'll take that on board. But its not so much the RCD tripping as the Megger internally tripping whilst attempting to gain the reading.

Any ideas? Is it a design fault or have I done something wrong?

:-/

 

[Spudnik]

In what way does it 'internally' trip?

 

[Big Man]

It comes up with TRP on the screen. I assumed it is a safty feature or prevents the RCD from tripping so you don't have to run off to the consumer unit. Either way I don't get a reading.

 

[Gravid]

I've used the 1552 before and i got this when either one of my connections wasn't firm enough, or if the leads weren't pushed home in the tester or the croc clips.

Maybe your testers developed a loose connection have you dropped it?

 

[mikeymoo]

U'll also get the trip msg if you move the probes. I had the same problem. Try using all 3 clips and make sure u have a good connection on the earth clip.

 

[acvc]

Big Man. I had the same prob. Have you got new leads, changed them recently? If they're fused leads, check the rating of the fuses, they should be 10A for the 1552. For me, it was a case of RS giving me 0.5A fuses for my leads and I didn't notice before I put them in. It had me baffled for a while. .