Megger 1552 (Hi current test not tripping 30ma rcd)

[DavidO05]

Hi guys, I own 2 megger mft 1552 testers.

I recently found that loop readings on both testers give me high Zs readings on final circuits protected by 30ma rcds on low current.
If I select the hi current setting I get a reading I expect to achieve, but the hi current test never trips the rcd.

Both testers have been calibrated in the last 3 months

Any advice?

Many thanks David

 

[Sintra]

What make are the RCD’s as I had the same issue with Hager RCBO’s a few years ago. They all tested fine whilst doing the RCD trip times.

 

[buzzlightyear]

I recently found that loop readings on both testers give me high Zs readings on final circuits protected by 30ma rcds on low current.

try using the three probes .

 

[DavidO05]

the Rcds are MK mainly but it’s recently happend on a CPN rcd aswell. It seems to be more on the recent metal clad dbs, I don’t know whether they have altered the rcds in anyway

 

[buzzlightyear]

No its the same way ,i use a megger and i find no difference.have you changed the test leads by any chance.

 

[DavidO05]

The test leads on one of the instruments is brand new. Everything else about the meter is still giving decent readings

 

[freddo]

A workmate had the same model and was getting silly loop readings. Bought a new set of leads thinking it was that, but they made no difference, work sent it away for repair and calibration but was still the same when it came back so it's no longer used. The test readings have never really been very repeatable with it.

 

[static zap]

Hi guys, I own 2 megger mft 1552 testers.

I recently found that loop readings on both testers give me high Zs readings on final circuits protected by 30ma rcds on low current....

What supply TT , TN-C-S ?

 

[buzzlightyear]

I recently found that loop readings on both testers give me high Zs readings on final circuits protected by 30ma rcds on low current.

http://www.free-instruction-manuals.com/pdf/pa_359466.pdf MILLION WORDS

 

[static zap]

try using the three probes .

@buzzlightyear
Are you implying the test where the RCD is in effect bridged by the MFT
and the far end of the circuit tested for Zs modified ?

 

[DavidO05]

What supply TT , TN-C-S ?

It’s on both tn-s and tn-c-s. I’m yet to use it on a tt system.
I have spoken to megger technical. They said to use the hi current reading and just to do a ramp test to ensure the rcds are tripping at an acceptable Ma. Just seems bizarre it’s with both my 1552 testers

 

[HappyHippyDad]

It’s on both tn-s and tn-c-s. I’m yet to use it on a tt system.
I have spoken to megger technical. They said to use the hi current reading and just to do a ramp test to ensure the rcds are tripping at an acceptable Ma. Just seems bizarre it’s with both my 1552 testers

It's good that you have 2 testers as that kind of signifies that the problem is with the 'type' of tester rather than perhaps an actual fault with the tester or a fault in the installation. It would be even better if you could try a different type of MFT on the same RCD's then you could narrow the problem down depending on if the different MFT managed to trip the RCD on high current.

 

[DavidO05]

It's good that you have 2 testers as that kind of signifies that the problem is with the 'type' of tester rather than perhaps an actual fault with the tester or a fault in the installation. It would be even better if you could try a different type of MFT on the same RCD's then you could narrow the problem down depending on if the different MFT managed to trip the RCD on high current.

I asked a guy that works with me to get his tester out aswell, which was only a week old. His tester was working accurately.
We done a loop test using the megger and his di-log on either side of the rcd. The megger recorded .50ohm difference, where as his tester recorded no difference at all.