testing 4 pole RCD - funny results?

[EastAnglian]

Can anybody help with this one?

Installation: TT system, (Ra 27 ohms), 3 phase & neutral incoming supply.

A 4 pole 30mA RCD is at the head of the board, from which there is a 3 phase motor circuit and a 3 phase & neutral feed to a second board. The second board has a number of 230V final circuits fed from each of the phases in turn.

When testing the RCD I get a figure of about 120mS at 30mA test current but at 150mA test current the test bombs out at >40mA. I can't actually configure the test set to record the operating time at 5 x Idn.

I changed the RCD for a new one and I get the same result.

I started off by testing this at one of the 230V final circuits. However, I get the same result if I test directly on the output terminals of the RCD - i.e. L1, N, CPC - ditto L2, L3.

I have checked the tester on a 2 pole 30mA RCD and I get the normal sort of operating times you would associate with a fully functioning device.

Any thoughts on the test method, or a configuration fault which might give longer than expected cut-off times?

 

[Leesparkykent]

Disconnect the load side from the rcd and test again at the terminals.

 

[PEG]

Can anybody help with this one?

Installation: TT system, (Ra 27 ohms), 3 phase & neutral incoming supply.

A 4 pole 30mA RCD is at the head of the board, from which there is a 3 phase motor circuit and a 3 phase & neutral feed to a second board. The second board has a number of 230V final circuits fed from each of the phases in turn.

When testing the RCD I get a figure of about 120mS at 30mA test current but at 150mA test current the test bombs out at >40mA. I can't actually configure the test set to record the operating time at 5 x Idn.

I changed the RCD for a new one and I get the same result.

I started off by testing this at one of the 230V final circuits. However, I get the same result if I test directly on the output terminals of the RCD - i.e. L1, N, CPC - ditto L2, L3.

I have checked the tester on a 2 pole 30mA RCD and I get the normal sort of operating times you would associate with a fully functioning device.

Any thoughts on the test method, or a configuration fault which might give longer than expected cut-off times?

The above,may possibly be a clue,to what Lee has already mentioned :rolleyes2:

 

[i=p/u]

maybe 100mA rcd loool

 

[i=p/u]

might be overlookjed like ive done before

 

[EastAnglian]

might be overlookjed like ive done before

No, even I thought of that one - it really is 30mA

 

[EastAnglian]

Disconnect the load side from the rcd and test again at the terminals.

Thanks Lee - I thought I had done that, but will check again tomorrow.

 

[EastAnglian]

Disconnect the load side from the rcd and test again at the terminals.

Good call Lee ....... turned off the 3 phase motor load and a good set of results on all phases

So what's the explanation? Back EMF off motor windings spooking the RCD tester?

Cheers

Malcolm

 

[Leesparkykent]

Good call Lee ....... turned off the 3 phase motor load and a good set of results on all phases

So what's the explanation? Back EMF off motor windings spooking the RCD tester?

Cheers

Malcolm

When you have a bit of spare time read this mammoth thread lol

http://www.electriciansforums.co.uk...ical-forum/103889-whats-mean-rcd-test-10.html

 

[Simonslimline]

An RCD test should always be carried out at the device with all loads dissconnected.

Not doing it this way can give duff readings as you have proved to yourself.

Glad you got it sorted anyhow.