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Posted By Topic: HEM RCDs

Nov 24 2018 20:11

Checked a new installation with 3 RCDs - 2 HEM and 1 Schneider. One of the HEM RCDs was OK but the other returned variable results when tested. Over about 10 tests at 1xIn, it did not trip at greater than 300ms (50% of the time) or it tripped between 9.01 - 18.4 ms.
I have recommended that it be replaced. Anyone had problems with this equipment?
Tested with Megger 1835.

Nov 24 2018 20:15

did you remove ther loading from the RCD wgebn testing? If the load is capacitive or low inductance, your RCD tester can NOT test RCD and will give stray results.

Nov 24 2018 20:41

Yes. The other 2 were OK.

Nov 24 2018 22:07

I am just going to chime in here with a simple question.

Why were you using a fancy tester on a new installation.

All that is required by AS/NZS3000:2007 section 8 is that when the RCD is tripped it disconnects the supply.
Section says The RCD shall disconnect the circuit. There is no mention of time or any reference to a standard that covers tripping times.

As the installer you are entitled to rely on the SDOC for the item. This confirms that the manufacturer has done all the testing to ensure that the product complies and is safe to install and use.


Nov 25 2018 11:30

ESR24 specifies the criteria for a RCD to be electrically safe.
Surely you would need to test and confirm the installation met this as there are numerous things that could deem the RCD unsafe after it has been factory tested.
At the end of the day it is your name on the COC/ESC confirming it's electrically safe.

Nov 25 2018 12:12 gives you 2 options of testing RCD's, simply by pushing the built in test button or by using test equipment.
Test button is the quick and easy way, quite often at the end of a new build as part of the contract as builts and test results are required and this includes actual RCD test results which includes trip times and trip currents, and this does help to identify other potential issues.

Either method is acceptable

Nov 25 2018 12:21

ESR 24 does NOT require testing of RCD, regardless of new or old.
And if you read the ESR (6 or thereabouts) that does require testing of PEW; you won;t find anything about testing as per ESRs, you'll only find testing as per 3000 (and other relevant cited Standards).

Remember too that RCDs are DHRAs, so anything on our market has not only been tested to manufacturing Standard but has been Approved by Worksafe.

When you do decide to (voluntarily, or for fault finding) test an RCD, you need to remove all the wiring on the output to be avoid capacitance of cables from affecting the results. And you need to be working on a supply of appropriate waveform, with no distortion from non-linear loads elsewhere (within the installation or external).

Field testing cannot ever be as good as lab testing; it can only ever give an approximate result. You can't be certain that these units are "bad", but you certainly have cause for suspicion.

Nov 25 2018 14:56

Regulations 59, 60 & 63 all require testing to AS/NZS3000:2007.
The only section of AS/NZS3000:2007 that deals with testing is section 8 and the RCD section is 8.3.10.

Nothing in there about time of tripping.

The people who sell these fancy testers all tell you that you have to have one and that testing using their fancy machine is mandatory.

Simple reading of the standards shows that this is not true.

As the installer of the RCD / RCBO you are entitled to rely on the SDOC for compliance with tripping currents and times. As the installer you are required to verify that when the RCD trips it disconnects the supply from the load in all poles.

All the stuff in the ESR’s about electrically unsafe RCD’s is directed at the importers and suppliers of these items who issue the SDOC.

As Aleck says unless you have a test house and calibrated test equipment your field tests are just indications that there may be a problem.

It will be interesting to see if the problem is repeatable with the RCD connected to a different power supply and no other field cabling connected.