Whats this mean on a rcd test

[Maxstone89]

I think i know but want to make sure

 

[davesparks]

If the test current produced by the tester is then subject to resistance between the tester and the RCD, what current would be detected by the RCD?

Exactly the same current as the tester produces. Current does not diminish through a circuit.

 

[Deleted member 26818]

Exactly the same current as the tester produces. Current does not diminish through a circuit.

Lol.​Lol.

 

[davesparks]

Lol.​Lol.

What is that supposed to mean? Of you think I'm wrong please explain.
Current does not diminish at it travels through a conductor. If what you are suggesting was true then you wouldn't ever see any current in the neutral!

 

[Dave OCD]

After 7 pages of all this (and yes I know the approved way of testing an RCD), I still like to test the RCD at the circuit/s I've worked on [such as additional sockets for example].
It's just good to know that you're actually simulating a fault where it might actually happen and seeing the disconnection times at the business end of the circuit as it were, gives me additional peace of mind.

 

[davesparks]

After 7 pages of all this (and yes I know the approved way of testing an RCD), I still like to test the RCD at the circuit/s I've worked on [such as additional sockets for example].
It's just good to know that you're actually simulating a fault where it might actually happen and seeing the disconnection times at the business end of the circuit as it were, gives me additional peace of mind.

So you get better peace of mind carrying out the test in such a way that could give a false pass?

Any earth leakage on the outgoing circuits will bias the RCD to trip at a lower test current than if it was tested in isolation.
With a 10mA existing earth leakage the tester could apply 30mA test current to trip the RCD yet the RCD is seeing 40mA before it trips.

 

[Dave OCD]

No I do it at the RCD initially, for the sake of a few seconds I also do it at the end [unless it's a RFC] of the circuit/s in question - with all other final circuits switched off. So assuming the circuit in question has already undergone dead testing and produced good insulation resistance results how can there be earth leakage to confuse the tester ? If anything I'd expect to see slightly higher tripping times at the end of the circuit.

 

[davesparks]

No I do it at the RCD initially, for the sake of a few seconds I also do it at the end [unless it's a RFC] of the circuit/s in question - with all other final circuits switched off. So assuming the circuit in question has already undergone dead testing and produced good insulation resistance results how can there be earth leakage to confuse the tester ? If anything I'd expect to see slightly higher tripping times at the end of the circuit.

If the tripping times change due to the tester being at the end of the circuit then the RCD is faulty. If anything it may be quicker as RCDs tend to get a bit quicker after a few operations.
The tripping time will be exactly the same wherever you put the tester assuming that there is no earth leakage to interfere.
As far as the IR results go, what exactly are you calling 'good'? If there are a number of circuits then their combined insulation resistance may be quite a bit less than the individual circuits

 

[Dave OCD]

Tripping times are never exactly the same, if I'm getting >10 Megohms on older installations I'd say that was good, would expect to see >200 on new wiring though.

 

[davesparks]

Tripping times are never exactly the same, if I'm getting >10 Megohms on older installations I'd say that was good, would expect to see >200 on new wiring though.

Only 200? I'd expect a damn sight more than that on new installations.

 

[Dave OCD]

Yes of course more like >2000 but just based the reply on a commonly used figure- possibly older testers showed >200 as their upper limit ?

 

[Deleted member 26818]

Only 200? I'd expect a damn sight more than that on new installations.

I think that will depend on the brand of tester being used.

 

[GB.Kayak]

Oh my goodness. I'm done here lads.
No forther comment. I wouldn't want to force anyone's hand into banning me just 10 minutes after I came back.

What trev red carded ... never! I really must log in more often!

 

[NDG Elecs]

Right! On your schedule of test results have a free line above each set of RCD protected ccts. Put on that line RCD 1/61008/x1/x5 results....then on your next line start the various cct details, and you can then also detail individual cct RCD results if you so wish...

That way everyone is happy (cept maybe DS!) !!

Good to see Trev back...

 

[Deleted member 9648]

I dont think I have ever come across such a hair splitting thread on this forum before. As long as the thing trips WTF does it matter.

 

[Risteard]

I am a firm believer in RCDs being tested in isolation.