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Slightly confusing electrical issue with RCD kicking in

Postby Zeeflyboy » Mon Jul 05, 2021 8:54 am

Hello chaps/chapettes,

I have a bit of a noodle scratcher that I hope someone can help shed some light on.

So simply the problem is that yesterday morning, an RCD in the consumer box kicked in several times. I thought I had narrowed the problem down a faulty surge protector as it was then fine the rest of the day, but kicked off again last night. It reset and was fine all night then kicked off again this morning.

I have a garden studio, which is supplied from the consumer box on its own 32A MCB and armoured cable, installed around 5yrs ago with no issue. I couldn’t re-engage the RCD this morning without first turning off the MCB to the studio, which seems to narrow it down to an issue there.

Now for the part that’s confusing!

I have managed to track it down to a motion control unit for a motion sim I built, but that was plugged in but not turned on. However it’s seemingly confirmed as the problem because this morning if I unplugged the IEC connector then the RCD could reset, and the moment I plugged in the IEC it popped again (plug still turned off). There are 5 VFDs each with their own EMI filter in the box so logical there may be leakage issue.

This fact that it trips with the socket off suggests a Neutral-Earth fault, however the studio is on a single pole MCB so should only cut live… so if it’s a neutral-Earth fault then why did flicking the MCB allow the RCD to reset?

To further confuse things, nothing changed in the configuration over night, it was plugged into a turned off socket all this time, but only seemingly randomly trips (nothing in the studio is on a timer or anything).

Also, after trying the IEC cable and finding it tripped, I plugged it in using a different shorter IEC cable through an extension cable and that didn’t trip, but the original IEC cable on its own doesn’t trip either, only when connected to the motion control box.

Anyone got any bright ideas what might be going on? Thanks for any ideas!
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Simply Build It

Postby Mr White » Mon Jul 05, 2021 7:26 pm

As you say it does appear to be a problem with the device you built, since we have no idea what it consists of I do not see how anyone can directly help you.
However what I will say is you really need to get all circuits tested, as it may just be that your device naturally leaks and it is something else that is leaking but your device is just tipping it over the edge.
It is not unusual for computers to leak.
Mr White
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