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Rcd Tripping When Main Switch Turned Off


monkey5

Question

afternoon all.

just a query as never had this before, was at customers for some thing different when I was doing a test at consumer unit, isolated all mcbs and turned the main switch off, as I did this the RCD tripped, normally would turn RCD off too before main switch but for some reason didn't.

was thinking possibly due to power being disconnected the RCD tripped but never had this before, has anyone else? did it everytime I tried after so not a one off.  tested RCD for time and ramp and all normal as was IR between neutral and live bars.  CU is a cheap and nasty proteus..

cheers

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6 answers to this question

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Proteus probably explains it....

 

Sounds like main switch possibly doesnt isolate Line and Neutral at exactly the same time.

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As Binky says

Prob line and neutral do not isolate at same time....and it is Proteus!

PROTEUS........THE "choice" of nobody, ever!

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Yes probably it breaks the N first, and there's probably a bit of leakage between N and E. With the N opening first the amount of leakage momentarily increases enough to trip the rcd.

 

My guess if you do some IR testing you will find one circuit has a little bit of leakage so this is an early indication to have a look.

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I had a job many years ago to do garden lighting and power.Sub main to new C/unit as'16th' edition board, 30ma rcd and main switch. Same problem , so swapped rcd, even reversed polarity. Worked out it was the new pond pump. Got a replacement pond pump, no difference. The C/unit was used as local switching so no other isolators. All we could think of was the pump was continuing to spin when the breaker was switched off causing the rcd to trip.I gave up after that, customer said its ok but never got any more work from them.

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It makes you wonder how Proteus are still going. Every electrician i know, and the online community of sparks hate the stuff (and rightly so, its garbage)

 

Some fools must be buying them. Buy cheap buy twice.

 

From, a self confessed hager man. 

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Wickes sell them, so builders buy them. I decided I hate them when a 'failed cct' was actually allowing 200V through the MCB, so appliances all gave the appearance of being dead, but there was enough leccy to do me harm!!!! :red card

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