This is driving me mad

[johnM20]

Apologies in advance if this post gets a bit long but I believe all the details are needed for someone to give me an answer.

For many years I have run a pump in my garden pond and some garden lights via a single plug in timer and a double gang switch, one for each of the 'appliances'. The single live feed to the switch used a link to join the two parts of the switch. From the switch there are two positive wires, one from each individual switch (plus the single neutral and earth coming from the plug in the timer). This has presented no problem other than the lights could only be on when the pump was running as that is what I needed to control timewise, or vice versa.

However, I decided that if I used two plug in timers with a bit of rewiring, taking the link out between the two gangs of the switch and having a new live supply from the second timer I could have the pump running and the lights on independently. I joined the new earth and neutral to the existing earth and neutral.

When I switched on the pump it worked fine and when I switched on the lights they also worked OK but as soon as I had them both on together the trip activated. After a couple of times doing this I checked all my wiring and it all looked OK. Thinking about it overnight I decided that it was possibly because I had joined in the new neutral and earth but couldn't think why this should cause a problem but as a trial I disconnected these from the existing circuit. After all, all I was trying to do was to replace the link in the switches with a direct positive feed via a second timer.

As another trial I had the pump supply via the plug in timer and the lights direct from a socket. That worked OK so my belief is that it is something to do with having two timers. A change of timer didn't alter the results. It still tripped.

Can anyone offer any explanation before I go completely mad. Thanks in advance.

[Someone-Else]

In focus pictures of your wiring/switches and what is tripping will help. (Oh, and its live when a.c. is concerned not positive)
Please tell me you have NOT connected the earth to the neutral

[ericmark]

Actually live means line and neutral, they are both classed as live, so it would be line not positive, however it does seem that earth and neutral are connected some where, a RCD detects an imbalance so what goes out of one live wire must return on the other, if not then the RCD will trip.

A earth to neutral fault can be hard to find, as for current to return vie the earth instead of neutral there needs to be a voltage differential, and the more current flows the greater the differential, so a fault with a toaster can trip the RCD when kettle is used.

An isolator switches all live wires, a switch often only switches off the line, and back on your supply the earth and neutral are connected, not in your equipment but in the DNO supply, so before you can test an isolator needs to be turned off, MCB's don't isolate, even some RCBO's don't isolate but some do, stand alone RCD's normally do isolate.

So with isolator off there should be at least 1Mohm between neutral and earth measured using a insulation tester which normally used 500 volt DC to test with, some can be switched to 250 volt DC.

You can measure the leakage with a clamp on ammeter clamped over both line and neutral, should be less than 9 mA and for a single circuit without doubled up earth wires think it was 3.5 mA, would need to get book out to check. All my circuits (14 in all) together show around 25 mA but that is shared between 14 RCBO's so no problem.

AC can transfer by inductance and capacitance as well as simple resistance, so there is always some leakage when measuring the AC, but with DC there should be no leakage, but as @Someone-Else says, you should not be working with electric without some test equipment, what do you have?

[Bob225]

It's the timer, some timers only switch the live only, with neutral passed through this can trip a circuit

What make and model timers ?