RCD Question

[mnbs 4x4]

Hi Guys, a quiery for you, ( by the way I live in Western Australia) I was doing some work at the house today and was disconnecting some sockets for renovations, so i isolated the circuit but had to cut the T&E to get it out at the other end. Now the thing is that I have 3 phase incoming red phase protected by DP RCD, White(Yellow)phase the same and blue phase non protected circuits, each rcd protected phase has a mixture of power and lighting(thats the regs over here)
So when I cut the T&E I was expecting the white phase RCD to trip out but it didn't so i stripped it back and touched N and E together but no trip. I put a socket back on and plugged in my Robin digital RCD tester and did the x1/2 test which didn't trip(correct) then x1 at 30mA and tripped at 18mS at 0 degrees and 9mS at 180 degrees.
I've been sparkying for 22 years and have always believed N and E shorted out will trip an RCD, correct me if i'm wrong but can anyone shed some light on this.
The type of earthing arrangement over here is (crap) TPandN supplied by service provider then the spark installs an earth rod with a 6mm from that to the earth bar then an MEN link from earth bar to N bar.
Thanks

 

[malcolmsanford]

If we are going to assume everything is ok with your system, and it looks like it then off the top of my head I can only think that perhaps when you touched N/E together on the circuit it never tripped because the mechanism had some dust or was siezed.

Do you regularly test the button? After doing the tests with the tester, does the RCD trip now when you touch N/E together?

I would also ramp test the RCD if you can, the RCD tester will give you the timings, a ramp will tell you the trip mA.

 

[Deleted member 26818]

When you cut the T&E, was the red phase RCD isolated?

 

[mnbs 4x4]

Thanks for the replies guys, This afternoon i did some poking around , I disconnected the main earth from the earth rod , everything about it was very corroded, rubbed it back to shiny copper , remade the end and fitted a new clamp and hey pesto all fixed, it must have been like that for years(very worrying to think about it). Went back to the board and shorted out Earth to red phase neutral bar and white phase neutral bar and both RCD'S tripped.
This just shows that you can't be to reliant on testers , as my rcd tester was still causing a trip.

 

[telectrix]

that may be because when you shorted the N and E, the E was not earthed due to the corrosion you found. therefore the RCD did not see it as a fault.

 

[johnboy6083]

Thanks for the replies guys, This afternoon i did some poking around , I disconnected the main earth from the earth rod , everything about it was very corroded, rubbed it back to shiny copper , remade the end and fitted a new clamp and hey pesto all fixed, it must have been like that for years(very worrying to think about it). Went back to the board and shorted out Earth to red phase neutral bar and white phase neutral bar and both RCD'S tripped.
This just shows that you can't be to reliant on testers , as my rcd tester was still causing a trip.

when you did external fault loop impedance test, that would pick up a dodgy earth connection.