RCD tripping times exam question

[Dave the spark]

I sat the 2394 written exam tonight and one of the questions was about testing a 30mA RCD.

It asked which tests you would carry out and the permitted tripping times.

I answered that at 30mA and 150mA it was equal to or less than 300ms and 40ms respectively. Which I believe to be within those parameters

Is this right because I'm now unsure if it should just have been less than rather than equal to or less than.

 

[Pat H]

Pretty sure that's correct.
The 1/2 shouldn't trip of course.

 

[Dave the spark]

Pretty sure that's correct.
The 1/2 shouldn't trip of course.

Yeah, so went through each test at positive and negative for each of the operating currents and gave the times no trip at 15mA, equal to or less than 300ms at 30mA and equal to or less than 40ms at 150mA.

I know these times like the back of my hand, it's just someone said after they thought it was less than rather than equal to or less than. Then when I looked in GN3 the wee arrow didn't have the double line to signify equal to, just less than.

 

[Pat H]

Pretty sure its within 300ms so tgat would include 300ms and less.

 

[Risteard]

It depends whether it is an older BS type or a newer BS EN type. For the older ones it was within 200mS - for the newer ones it is within 300mS (at I delta n).

 

[Richard Burns]

The wording in the regs is not exceeding 40ms.
Therefore 40ms is acceptable and can be described as less than or equal to 40ms, etc.

Sockets with integral RCDs to BS7288 still have a trip time of 200ms at I delta n.

 

[Dave the spark]

Ok, cheers lads.

I don't suppose anyone knows what the pass mark is? I've read 60% but that seems low as you could drop 36 marks out of 90!

 

[Dave OCD]

And they might want operation of the test button included in the answer to that as well as the other tests.

 

[westward10]

They often ask what are the 7 tests to be carried out for an rcd, nearly threw me once, as Dave says the 7th is the manual operation.

 

[Pat H]

Don't forget we don't need to do the X5 on RCDs over 30mA as they don't offer additional protection.

 

[Risteard]

Don't forget we don't need to do the X5 on RCDs over 30mA as they don't offer additional protection.

Indeed, but it's surprising how many don't know that. Even the test equipment auto test sequences erroneously carry the tests out for RCDs with a rated residual operating current exceeding 30mA.

 

[Dave the spark]

They often ask what are the 7 tests to be carried out for an rcd, nearly threw me once, as Dave says the 7th is the manual operation.

And they might want operation of the test button included in the answer to that as well as the other tests.

That was a separate question. -Functional test of mechanical test button