i have just put power in my shed and when i switch the fuse box on alls fine switch the light on and the rcd trips plug anythink in the sockets and it trips i checked the wireing in the fuse box at both ends and throughout the circuite theres no wires touching and everything looks fine its about a 25 to 30 foot run the rcd is 40amp - 30 ma with a 5 amp mcb for a light and 20 amp for 2 double plugs. the wire iv'e used is 4mm t-e . do i need to put in a seperate earth rod and wire would this help

bones, October 2008

Hi all, I consider myself a bit of an amateur electronics expert as I design and build process control systems for fun, yet I battled for weeks with a spurious RCD tripping problem that I couldn’t pin down. I did all the usual isolating circuits and changing RCD etc and even went down to using a oscilloscope to monitor back emf pulses on time/thermostatic switching devices (heating pump for example) as well as testing resistive, capacitive and inductive factors between live, natural and earth to see if this could explain an imbalance between live and natural. Despite the fact that the law of electronics says that if you disconnect and reconnect a circuit, no matter how quickly and in no matter how short the bursts, the current in live should match that of natural (assuming no earth fault) and hence no RCD should tip by switching something on and off quickly, in the end I think I pinned the problem down to a plug with a lose natural screw!!! On further investigation it seems that the lose natural lead in a plug was causing sparking and bursts of short disconnections and reconnections due to movement (people walking in the room) and because the device plugged in was a modern large screen TV with a switched mode power supply it wasn’t obvious (IE TV didn’t flicker or anything because the power supply had plenty of reserve for the short breaks in mains) but the short burst in disconnection was making the switched mode power supply kick back some reverse emf which seems to be confusing the RCD into tripping. All in all I went round the house checking that terminals on any none molded plugs were in order and the problem seems to have gone away. It nuts I hear you say as it doesn’t make sense according to electronics law but that was what it turned out to be in my case :)

Ricky, August 2010

This task should now be undertaken by a Qualifide electrician under part p regulations all cables under 32amp need to be protected by an rcd plus all electrics considered to be able to be used outside must be rcd protected under the 17th edition of the regs. http://kmelectrical.webstarts.com

Km electrical, May 2010

can i change an cooker switch to a double socket, do i need change the rcd aswell?

dave, April 2009

hi
I suggest you disconnect your cables and meter them out to make sure that everything is clear, i believe you have an earth leakage somewhere and u should test for this first, good luck

Billy, October 2008

the rcd unit is there to protect you so if it does trip out from the rcd unit you no it is working and in sheds there is damp this tends not to help the unit it trips straight away

syd, October 2008

im useing a volex garage unit 1 rcd a 6amp and a 20amp the rcd is in the shed cu.

bones, October 2008

Where is the rcd which is tripping? Is it mounted on the a sub-consumer unit in the shed or is it on the main board?

The lights in the shed should not be protected by the shed rcd - so switching on the shed lights should not be tripping that rcd. Only the sockets should be protected by the rcd.

J, October 2008

When you use any power in the shed (light or socket) the 30mA RCD says there's leakage. Either there's leakage associated with BOTH the light circuit AND the power circuit OR the leakage is coming from somewhere else. I suspect the cable running to the shed. If you've put a nail through the neutral wire for instance, the RCD would not trip until you attempto draw current. But what do I know? A: Very little - take expert advice.

Richard Buxton, October 2008