RCD testing issues

Hi all,

Been a while since I have been on here. I have been on an apprenticeship the last 3 years training in the BMS world. Taking that into account, I have not done any testing for the last 3 years so please be gentle with the below.i feel very rusty.

My neighbour has asked for my help with RCD nuisance tripping. His little brother has temporarily moved into his spare room and brought with him some computer gear. Since then the main RCD has tripped a few times (once in the middle of the night). Finger is firmly pointed at this being the issue.

I have done an earth leakage test on the board. No circuit is causing any more than 2mA of leakage (with all the PC gear turned on).

I tried to test the 30mA AC up front RCD directly with all circuits isolated but it would not trip, it would however trip if I tested from one of the circuits (when energised). My first head scratcher. The trip time was 15mA at x1.

I did attempt to move the upstairs sockets onto the non RCD side of the board as a temporary measure to see if the problem persisted however, as soon as I moved the neutrals to the non RCD neutral bar, it tripped the rcd. My second head scratcher.

I have ran out of time because I needed to take the kids swimming but my thoughts are, the RCD is faulty considering the 15mA trip current. The upstairs RFC which I attempted to move to the non RCD side must be connected to the RCD somehow via a shared neutral or similar.

Would be good to hear your thoughts.

The board is an Volex. RCD is a volex VR63.

You need to test the upstairs circuit and check any interconnections to neutral of the RCD side.
I wouldn't recommend removing it from the RCD even as a temporary measure.

westward10 said:

You need to test the upstairs circuit and check any interconnections to neutral of the RCD side.
I wouldn't recommend removing it from the RCD even as a temporary measure.

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Yeh I agree. I did do end to end test on the neutral RFC which came back as 0.95 ohms.

I will have to look at the circuit in more detail

gazdkw82 said:

I tried to test the 30mA AC up front RCD directly with all circuits isolated but it would not trip, it would however trip if I tested from one of the circuits (when energised).

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I'm suggesting this because it's a mistake I made once, when I wasn't thinking clearly: Did you test the correct side of the RCD?

I would be carrying out insulation resistance tests first, to rule out any faults in the circuits or equipment. Test L+N to E at 250V, with everything left plugged in/switched on.

Pretty Mouth said:

I'm suggesting this because it's a mistake I made once, when I wasn't thinking clearly: Did you test the correct side of the RCD?

I would be carrying out insulation resistance tests first, to rule out any faults in the circuits or equipment. Test L+N to E at 250V, with everything left plugged in/switched on.

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Doh. What a dumbo.

gazdkw82 said:

Doh. What a dumbo.

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The guy who made a basic error or the guy insulting those from whom he seeks assistance?

nicebutdim said:

The guy who made a basic error or the guy insulting those from whom he seeks assistance?

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Me, making such a schoolboy error. It's amazing how much you de-skill when you don't regularly do something.

Assumption is the mother of all major foul-ups!

Start with the basics, like IR testing, RCD testing on its own, and checking the leakage as circuits are powered on.

An RCD that fails to trip-test on its own is deeply suspicious, but until you have ruled out N-E faults an anything still connected (i.e. it is not really "on its own") there is no point in jumping to that conclusion.