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RCD testing
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Bazzer  
#1 Posted : 16 September 2010 10:17:38(UTC)
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Bazzer
I have a client who has a woodworking workshop. All 13A sockets, for small power tools, which are double insulated are protected by RCD's fitted in the distribution boards. Now normally I recommend that RCD's are tested prior to use to make sure they operate correctly, by pressing the trip button. In this case I can't have the operator going into the distribution board pressing trip buttons, but I do however need to ensure that they operate when needed to. I am considering suggesting that the RCD's are tested monthly, even though the portable tools used are double insulated, but are not guaranteed to be; do you think this is reasonable?
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ahoskins  
#2 Posted : 16 September 2010 16:38:51(UTC)
Rank: Super forum user
ahoskins
I believe it is recommended that fuseboard RCDs are tested quarterly, but if you can set up a regime to introduce monthly testing then that would be a bonus. Don't forget that apart from the 'button' test, RCDs should also be tested for speed of disconnection by use of a commercially available RCD tester.
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Bazzer  
#3 Posted : 16 September 2010 16:48:26(UTC)
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Bazzer
Never heard of an RCD tester before; how does it work?
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PhilBeale  
#4 Posted : 16 September 2010 17:43:55(UTC)
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PhilBeale
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Grizzly  
#5 Posted : 16 September 2010 21:19:50(UTC)
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Grizzly
Cooper35245 wrote:
Never heard of an RCD tester before; how does it work?
The tester is able to supply a specified current imbalance between the L & N outputs of the RCD, and measure the time (in milliseconds) that it takes for the RCD to disconnect (trip). Hence, the RCD can be checked that it is operating within it's designed parameters. Some testers can also do a 'ramp test', which will measure the actual current difference that the RCD will trip at, which is less than the stated trip current (e.g. 30mA) for the majority of devices.
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paul.skyrme  
#6 Posted : 16 September 2010 21:39:19(UTC)
Rank: Super forum user
paul.skyrme
RCD manuf' requirements are RCD tests 1/4ly by test button. BS7671 requirement for skilled RCD test is in accordance with PIR recommendations. You cannot get a reliable RCD disconnection time test at a remote socket due to the laws of physics. BTW not ALL RCD's are 30mA, they are available in many other values as well as having special characteristics depending on the load, supply and requirements for discrimination. Monthly testing could be overboard, good, but, remember the device could be interrupting full load current and such devices are only rated at a finite number of full load disconnections before they require replacement. Undertaking competent RCD testing is a skilled test as it should be done within the distribution board with the board live, else you can't test the RCD! Paul
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Grizzly  
#7 Posted : 16 September 2010 22:41:16(UTC)
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Grizzly
paul.skyrme wrote:
BTW not ALL RCD's are 30mA...
Hence the 'e.g.' ;-)
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