RCDs and the Importance of the Test Button.

[telectrix]

done a small job today. just a socket & SFCU ( for a light) in customer's shed, on existing feed. feed cable is 2.5mm on a 16A MCB, RCD protected. cable tested OK, installed bits. Zs 2.4Ω. ramp test of RCD, mft reads>51mS. prerssed test button on RCD (which the customer said had never been done or RCD tripped in 15 years). then re-tested. ramp 27mS. times... 32mSec@ x1. 9mSec@ x5. just goes to show that they can get sticky.

 

[Harryb]

Has the shed got its own board with an exported dno's earth? Lol

 

[GLENNSPARK]

done a small job today. just a socket & SFCU ( for a light) in customer's shed, on existing feed. feed cable is 2.5mm on a 16A MCB, RCD protected. cable tested OK, installed bits. Zs 2.4Ω. ramp test of RCD, mft reads>51mS. prerssed test button on RCD (which the customer said had never been done or RCD tripped in 15 years). then re-tested. ramp 27mS. times... 32mSec@ x1. 9mSec@ x5. just goes to show that they can get sticky.

yes....
and how many customers take any notice of the test quarterly sticker....or are shown functional operation on handover...

 

[R G]

Has anyone seen the article on RCDs in the ESC swtched on mag , ESC takes a look at adequacy of RCD main contacts , it's amazing what damage can be done with high fault currents to these contacts , something to consider about the quality off them !!!

 

[telectrix]

Has the shed got its own board with an exported dno's earth? Lol

unfortunately, no to the 1st. and yes to the 2nd. shed is fed with a 2.5mm T/E in plastic flex conduit direct from MCB in CU. it's been there for 18 years, and the job was " stick us a socket and a light on that, mate". " as long as it tests OK" was my reply.

 

[stuartcourt]

dont you need an earth stake bla bla ****ing bla

 

[Clive P]

HI,
The Company I used to work for had us pressing the test buttons on RCD's on over 200 sites every 3 months ( as per manufacturers instructions ). Needless to say we integrated this with other maintenance work. Once a year we tested the tripping times of the RCD's and tested the button last. As Tel says they can get a bit 'sticky'.

Regards.

 

[telectrix]

dont you need an earth stake bla bla ****ing bla

stakes are for pinning apprentices to the workplace.

 

[stuartcourt]

my bad

 

[farmerian]

Replace the dam thing

 

[GLENNSPARK]

interesting point here....
if...lets say you were on a practical examination for the (now defunct) 2391...and you performed RCD testing at X1/2, X1 & X5...but then did not perform the manual test by use of the devices test button then the lecturer should be noting it against you...
same as the written part of the course....
when asked how to perform testing for disconnection time on say a 30mA RCD ...and you reel off the sequence of tests correctly...but then fail to mention testing by means of the manual test button....there will be marks lost for that...
a typical 1 mark question would be :
how many tests are required for a 30mA RCD to BSEN61008....candidates stating 6 would not get the mark....

 

[Marvo]

I've come across many RCD's that fail on disconnection times and on a leakage current ramp test but then the pass after operating the test button a few times.

Surely if the customer isn't pressing the test button periodically then the RCD should be replaced if it fails tests before the button is operated because it's failing in real life conditions and even if it passes eventually after the test button is pressed, in reality it will not meet disconnection times again after another few months of nobody touching it.

 

[Deleted member 72666]

I was told on a recent 2395 course to test the rcd's before pressing the manual test button and one of the reasons amongst others of doing it in that order was that it could influence the test results. That argument could be difficult to prove or disprove I suppose.

 

[telectrix]

agreed. but the problem is that then thousands of RCDs would be condemned. just because manufacturers instructions were not folloewed.

 

[Marvo]

But those manufacturers instructions are aimed at the home owner who has no duty to follow them, not the electrician who does have a duty.