RCD Tripping Problem

[thearabstrap]

Hi Forum.
First post cos this has me scratching my head.

We have 3 single phase boards on an installation in edinburgh.
All 3 boards have tested fine and been certified as so.

However, we have been called back as one board keeps tripping when a hoover is plugged in.

There is a 30mA RCD as the main switch and this problem only occurs when the hoover is plugged in to either ring on this board. we have tried 2 different hoovers on this board and both trip the RCD but none of them trip the RCD on the other 2 boards. We have even tried an electric drill on the tripping circuits but it runs fine??????
Do vacuum cleaners leak much current?
Any help appreciated.

 

[paulrayner]

what else have you got on the curcits? computers etc ? the hover might just be pushing the eart leakage up far enough for it to trip.

 

[Mac]

what else have you got on the curcits? computers etc ? the hover might just be pushing the eart leakage up far enough for it to trip.

Why not on the other 2 boards.Have you tried changing the breaker

 

[martspark]

some rcds are sensitiver than others. it shud have the ms times on your certs check and see if that 1 is more sensitive

 

[Graeme Harrold]

If you have a ramp test function, try that too. might show up as an RCD on its way out. This will give you the trip current rather than the time..........

 

[Matthew M]

Hi Forum.
First post cos this has me scratching my head.

We have 3 single phase boards on an installation in edinburgh.
All 3 boards have tested fine and been certified as so.

However, we have been called back as one board keeps tripping when a hoover is plugged in.

There is a 30mA RCD as the main switch and this problem only occurs when the hoover is plugged in to either ring on this board. we have tried 2 different hoovers on this board and both trip the RCD but none of them trip the RCD on the other 2 boards. We have even tried an electric drill on the tripping circuits but it runs fine??????
Do vacuum cleaners leak much current?
Any help appreciated.

Sounds as if it is nothing to do with the hoover, could check this by trying something else with a big load (kettle, toaster). I guess you have an earth leak to neutral of something under 30 ohms, and plugging the hoover in causes the voltage on the neutral to go to 1 or 2 volts which then leaks down the leak giving you 1v/30 ohm = 33 milliamps leak.

I'd start by switching off the main switch on the offending board and measuring neutral - earth resistance without unscrewing anything. If it is over 1 Megohm then I'm wrong and you need another idea, if under then chase it.

But remember to turn off the main switch otherwise you are just measuring the n-e resistance on next door's pme connection. You can feel really silly after getting this one wrong - I did.