Discuss Reasons for RCD not tripping other than failure of the RCD in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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ianbrookes

Hi, are there any reasons apart from faulty RCD that can be tested and what sequence of tests should I follow ?

I have a 100amp main switch with two MCB protected lighting circuits, and then a BS EN 61008 80a 30ma RCD with two 32a sockets circuits, a 16a heater circuit and a 6a security alarm circuit.

The RCD fails 1/2 test 0 and 180.
Trips at 12.9ms at 5x.
Gives a reading >400ms at 1x.

I am using a certified (calibrated) MFT and testing from a local socket in the installation.

thanks.
 
Hi, are there any reasons apart from faulty RCD that can be tested and what sequence of tests should I follow ?

I have a 100amp main switch with two MCB protected lighting circuits, and then a BS EN 61008 80a 30ma RCD with two 32a sockets circuits, a 16a heater circuit and a 6a security alarm circuit.

The RCD fails 1/2 test 0 and 180.
Trips at 12.9ms at 5x.
Gives a reading >400ms at 1x.

I am using a certified (calibrated) MFT and testing from a local socket in the installation.

thanks.

Seems a very strange way to wire up a 16th edition board, putting the alarm on the RCD. It also may explian why you are getting the results you are.

As Simnpn says the 1/2 trip should not activate, the x5 trip is perfect and it's the x1 trip that is causing you the problems as it should be tripping within 300mS. It may be, due to your having something plugged in on it? or if your not isolating the alarm system. Are you making sure there is nothing plugged in.
 
sorry, 1/2 doesn't cause the RCD to trip - so that's right.

5x is a good result.

1x is the issue.

I didn't wire the board, just installed some new lighting and then tested. I didn't get any abnormal readings on EFLI, PFC etc. all earthing looks good.

normal appliances are plugged in: Freezer, Oven, Toaster etc.

should I try isolating the alarm system MCB and unplugging the appliances ?

even with the freezer etc plugged in I don't know why I get this issue (the science behind it).

I haven't come across this before.

Apart from appliances and alarm are there any other issues I should look for, i.e. specific to earthing or wiring?

thanks again
 
sorry, 1/2 doesn't cause the RCD to trip - so that's right.

5x is a good result.

1x is the issue.

I didn't wire the board, just installed some new lighting and then tested. I didn't get any abnormal readings on EFLI, PFC etc. all earthing looks good.

normal appliances are plugged in: Freezer, Oven, Toaster etc.

should I try isolating the alarm system MCB and unplugging the appliances ?

even with the freezer etc plugged in I don't know why I get this issue (the science behind it).

I haven't come across this before.

Apart from appliances and alarm are there any other issues I should look for, i.e. specific to earthing or wiring?

thanks again

And there in lies your answer. Unplug all your appliances and it will soon get there. Capacitors in freezers n fridges will store the charge from the tester and fool it into thinking theres no load....at least I think that's how to explain it. Err Malcolm, mind helping me out again buddy? :)
 
well it maybe the characteristic of that particular RCD, but you will get a higher triping time with things plugged in on the 30mA tripping becasue of the capacitance these will build up.

You may find also that if the RCD as not been tested in a few years, it could just be sticking, after all we all know how concientous customers are at the quarterly push button test. Try activating it a few times via the test button and try again.

You can of course fit a new one and see if that is any better, but to be honest I would try and unplug everything and isolate the alarm, work the RCD mechanism a few times and then test.

Try also testing it at the actually RCD on the supply side see if that makes it faster.
 
I think it may be an idea to see if you can check the rcd at the distribution by disconnecting the outgoing cable temporarily then seeing if it still does not operate within time. I would also borrow another tester just to cross check ideally one with a ramped test so you can see at what current it is actually going out at
 

Reply to Reasons for RCD not tripping other than failure of the RCD in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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