Re the off-load test requirement..
You will know, or should know some electrical equipment can have some natural leakage..
So if you were testing an RCD connected to circuit with loads with say 6ma of natural leakage already on the circuits..
how to you think that may affect your results?
Hi special location
as for your question I wouldn't expect the RCD to trip at 6ma leakage as the RCD is a 30ma and won't trip till it senses over 30ma difference between line and neutral.
I think you may have missed the point of what I was trying to illustrate to you..
You mentioned doing ramp tests.. (which although not required by BS7671 are a very good diagnostic test when doing fault finding)..
and doing the 15ma (1/2 trip current test), which is required by BS7671...
If you were doing either of these with unknown loads connected that have a bit of natural leakage..
this leakage can affect your test results..
e.g.
If you've got one of those basic polarity tester plugs that light up three neon's if it thinks the wiring is good..
due to the way they work there will always be some CPC current flowing..
( If you've also got a milliamp clamp meter, do a test and see what you get..
I have a couple, one that is just neon's another that warbles as well..
One has a 4.2ma CPC current the other 3.1ma current.. )
So if doing a ramp test on a circuit with 5ma of leakage already present..
Your meter starts increasing its test-tripping current..
but the reading you get will be approx: The RCD's actual tripping current, minus the existing leakage current.
And if you were doing a 15ma no-trip test...
Your test meter puts out a 15ma CPC current,
But the RCD sees both your meters test current AND any existing leakage current..
which if I had my two test plugs connected at the time would be approx 15ma+4.2ma+3.1ma= 22.3ma
Which technically is within the valid range for a 30ma RCD to trip..
(Remember RCDs must trip fast enough with a 30ma or greater CPC current.
But they can also trip at lower values providing it is above 15ma..
see reg 531.3.2. & section 11 of On Site Guide)
I have seen many real world installed RCD's who trip around 24ma upwards..
SO its not rocket science to see that a connected load with 8ma of natural leakage could mess up your readings if testing with loads still connected!
( They can also have a negligible effect upon the trip times..
But in the real world it is very unlikely that the RCD is anywhere near its max permitted trip time, so that isn't a problem. )
Guinness