RCD Testing

[Bright_Spark]

Hi all.

Does anyone know where i can find detailed explanations of all 6 RCD tests? how/why theyre done etc?

cheers

'Bright Spark' (still learning)....or on this occasion '(not so) Bright Spark (still learning)'

 

[Spark123]

The 0.5I+ and 0.5I- tests are done to prove the device is not over sensitive and will cause nuisance tripping. + and - tests are done to prove that a leakage on either half of the cycle will cause the RCD to function correctly. I + and I - tests are performed to prove the RCD will trip at its design current within the correct timescale i.e. BS4293/7288 <200ms, BSEN 61008/9 <300ms. (These times do not include time delayed RCDs.) If the RCD is providing supplementary protection against direct contact it should also be tested at 5I + and 5I -, which it should trip within 40ms. All of these tests need to be performed with an RCD test instrument. A final check is to press the test button on the RCD to ensure the test button works.

 

[Jaymack]

To add to the topic.

For TT installations, where there is a main time delayed RCD (with typical EF trip currents of 100 to 500mA), in addition to another downstream (say 30mA EF trip current for sockets etc), it is necessary to ensure time discrimination.

A 3:1 discrimination ratio is required between the two RCD's that are connected in series, and this must be verified before testing.
It means that the delayed RCD must have an operating current at least three times that of the non-delayed type. For example, to discriminate properly with a 30 mA device, a second connected on the supply side would need to have an operating current of at least 90 mA (in practice, a 100 mA RCD is likely to be used).
The test for the time-delayed RCD consists of applying 100% of the normal rated current, when the device should trip within the time range of:
50% of rated time delay plus 200 ms, and
100% of rated time delay plus 200 ms.
For example, an RCD with a rated tripping time of 300 ms should trip within a time range of:
(150 + 200) ms = 350 ms and
(300 + 200) ms = 500 ms

 

[Bright_Spark]

The 0.5I+ and 0.5I- tests are done to prove the device is not over sensitive and will cause nuisance tripping. + and - tests are done to prove that a leakage on either half of the cycle will cause the RCD to function correctly. I + and I - tests are performed to prove the RCD will trip at its design current within the correct timescale i.e. BS4293/7288 <200ms, BSEN 61008/9 <300ms. (These times do not include time delayed RCDs.) If the RCD is providing supplementary protection against direct contact it should also be tested at 5I + and 5I -, which it should trip within 40ms. All of these tests need to be performed with an RCD test instrument. A final check is to press the test button on the RCD to ensure the test button works.

does that apply to both one and two pole RCDs? and RCCB incomers? in fact, RCD's right across the board? - Doh! why dint i ask that to start with and save on typing!

 

[Spark123]

An RCD and an RCCB are one of the same, I can't remember seeing a single pole RCD/RCCB. I have seen an RCBO (RCD with integral overcurrent protection) which is single pole, the tests are the same for these.
There is a bit more info in this document if you are interested:
http://www.iee.org/Publish/WireRegs...iring_matters_inspection_and_testing_rcds.pdf

 

[sijaysee]

when a shower is on an RCD, how do u test it? its not like sockets where you can plug in ur tester and push the button. i suppose u put ur test leads on the cables at the pull cord using croc clips. is that correct?

 

[securespark]

There is also a ramp test you can do.....

 

[ebee]

Good answers.
Yes the ramp test (although not a requirement) can often be helpfull in determining how an RCD might actually perform in real life.
Many of them ramp up in In/10
Ie say 30mA RCD starts at 15mA then increases test 3mA at a time until trips or for 10mA RCD starts at 5mA then tries at 6, 7, 8, 9 &10

for In read I delta n (I do not have a delta button on my keypad)