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Posted By Topic: RCD on 63A plug construction site?

Sep 02 2014 20:58

Hello guys,

I gotten into a discussion today about the fact if we have to install an RCD on the 63A Plug on Construction sites.

I did install one to protect the plug where they generally plug the life savers in.
This will protect the cable who (against my advise) gets left on the ground and gets driven over at least 10 times a day.

As I read this in AN/NZS 3012 all final sub circuits should be protected by rcd. In my opinion the 63A plug is just that.

The other person argument was that they couldn't properly test the life savers as the RCD on the board tripped quicker.
And he reckoned this is how we do it in New Zealand as the life savers Neutral screened cables plugged into the 63A plug are all linked through and only protected by the overload at the board. He is in the understanding that that whole life saver supply chain in then the final sub circuit.
But that means we have 63A cables lying and hangin all over site that are not RCD protected?

Indeed the RCD on the Board tripped quicker and we solved that today by bridging out the RCD temporary so he could test the Life savers.

Your thoughts?


Sep 02 2014 21:39

On first reading what you say makes sense and reading the cited clause makes an RCD mandatory.
But looking further into the bowel of the standard brings me to Figure K1 which appears to illustrate an alternative to the scenario you describe.
The diagram illustrates what I take to be the standard wiring system for 'lifeguard' types of construction site wiring. No RCD's on the main feeds to the lifeguards.
Logically this means that a fault on one unit forex not take out the whole circuit / floor area etc.

Sep 02 2014 22:48

You are required to ptotect the cable from being run over so that shouldn't be the issue. There is no requirement then to have a RCD on the 63A outlet unless being used for portable tools. Can't think of any off the top of my head which do. I think the standard for construction sites has the requrements for cable protection from being run over.

Sep 02 2014 22:53

AS/NZS 3012 is what you need to read and show them about protection of cables

Sep 03 2014 08:59

If (as seems likely) the site is using ACS under Appendix K of AS/NZS 3012 , the interconnecting cable between the ACS units is not a final subcircuit but submains [K3.2].
The submain cable can use either direct or detachable (plug & socket) connection.
Either way RCD protection is not required.

The submain cable must not be "lying around all over the place"; it is construction wiring and must be properly located and connected as per 2.5 [K6.3].
Note that while it may be of the type known as "neutral screen", in practice it is installed as earth-screened.

The ACS system in Appendix K is an alternative to the normal rules for construction site switchboards. It is cited in clause
If used, it must be adopted "complete"; you can't cherry-pick some parts and ignore others.


Sep 21 2016 21:36

for testing the principle I use is: do not expose live terminals. No need for it. USE the proper test procedure. Do NOT put in temporary loops ( if one forgets to remove these, you would have a very bad and dangerous situation).
Easy way to test Multiple RCD's (in series)(and with a bit of luck all would trip without the use of a test transformer). also if one can not reset the first RCD because, say it is in a locked up area, than no more test as your test/mains supply is gneo after the first successful trip test. not good, as more test are required as per AS/NZS ....
So a small isolating transformer say around 300VA with proper overcurrent protection and a earthed neutral on the secondary side is all you need. NOTE: this supply is NOW :
But the second RCD (the unit you want to test can now be tested as may times as you like, without tripping the first unit. Plus of course the test results are for the unit under test (Not the best result of two units in series). This system is great for RCD's on boats, caravans etc. where the supply is RCD protected at or near the power-socket.
Once finished the test-transformer is of course removed form the circuit. Not to be left on site. Don't forget it is not an isolating transformer for safety, it is modified to be a RCD test transformer !
I have been using this system for a number of years and it works well. While testing the RCD in a boat or caravan make sure there is no load connected. a battery charger or water-heater easily overloads a 300 VA transformer.
With the suitable plugs and cord-connectors it is safe to use by a qualified person.
good luck and safe testing


Sep 21 2016 22:40

When the ACS system is correctly used testing of RCDs in the ACS components is never a problem.

When a Portable Socket Outlet Assembly (PSOA) is used (a heavy duty construction site approved multi-way box you can not test the RCD using the test button on the PSOA when supplied by the ACS. If you do so, more than RCD may trip.

But you can test the RCD in the ACS system which is in series with the supply to the PSOA, hence no need to test the PSOA RCD.

The PSOA RCD is used when connecting to the supply fromm other than a ACS system.