Timer tripping my RCD

[hasti]

Hi,

I've just installed an outdoor double socket with a built-in RCD circuit breaker, so I can plug my pond pump into it. However, because I don't want the pump operating 24/7, I have plugged the pump into a timer switch, which is plugged into a short extension lead going to the outdoor socket.

i.e.    [OUTDOOR SOCKET WITH BUILT-IN RCD]-->[socket-->timer-->plug]--->[POND PUMP]

The middle section with the timer is housed within a waterproof box.

This worked fine, until the timer reached the cut-off time - and the break in power caused the RCD to trip.

Is there any way I can resolve this problem, so that the timer can controller the power to the pump without tripping the RCD?

Many thanks for any advice you can offer!

 

[Geoff1946]

It just might be a transient, (brief voltage surge), created by switching the inductive load of the pump. You could try a plug with inbuilt "surge protector" if you can find one which will fit into the outdoor socket, or an extension lead with one in, to plug the timer into.  Alternatively try a different timer, as better ones should have suppressors on their contacts.

Pure guesswork:  No promises! 

 

[Murdoch]

So the pump works ok without the timer ?

 

[NozSpark]

Do you know if it's an active or passive RCD?

If you plug the pump in and then switch it off, ore remove the plug, what happened to the RCD?

 

[hasti]

Thanks for your responses...

Yes the pump, and everything else, works fine. If I removed the whole timer thing and just flicked the socket switch on and off at the appropriate times, it would work fine. It's just that, when the timer breaks the circuit, the outdoor socket with the RCD trips - just as it would if had my mower plugged in and cut through the power cable.

Just to be clear, it doesn't trip at a random time. It trips when the timer 'switches off' the power. For example, I set it all up yesterday, and set the timer to run the pump 10am-10pm. It switched off at 10pm, as intended, but didn't switch on again at 10am this morning. So, I checked the timer and it was showing 10pm as the current time - ie the second it cut the power at 10pm the RCD socket must have tripped and cut power to the timer. To get the pump going again, I reset the time on the timer and pressed the RCD reset button. 

I think it's 'active' - if that means I have to press the reset switch after it trips. You can see the model I installed here: https://www.amazon.co.uk/gp/product/B077D7NFH3/ref=ask_ql_qh_dp_hza

 

[Fleeting]

If your sockets already have rcd protection at the consumer unit there is no need for it at the external socket as well.

 

[hasti]

So, if I replaced the RCD Outdoor socket with a none-RCD outdoor socket, do you think that would do the trick?

 

[Fleeting]

So, if I replaced the RCD Outdoor socket with a none-RCD outdoor socket, do you think that would do the trick?

You need to confirm at the consumer unit if you have 30ma rcd protection for the sockets before you do that.

 

[hasti]

I've just checked the Consumer Unit and, where it says "RCD Controlled Circuits" it says"0.03A".

So, I guess replacing the outdoor socket for a non-RCD one would work?

 

[Geoff1946]

If you have a pond pump on the same RCD as other circuits bear in mind the consequences of it tripping. Pond pumps are by any standards high risk for faulting. 

You won't be pleased if it shuts down your freezer whilst you are away for a day or two.

My outdoor sockets are on a separate dedicated radial with their own RCBO.

 

[Fleeting]

I've just checked the Consumer Unit and, where it says "RCD Controlled Circuits" it says"0.03A".

So, I guess replacing the outdoor socket for a non-RCD one would work?

Turn off the rcd and see if the socket is no longer live, if it is dead then yes you can replace it but before you replace it plug the pump in by way of an indoor socket and see if it trips the rcd at the consumer unit. Press the test button on the rcd to see if it actually trips first.

 

[hasti]

Thank you, Fleeting. I'll do what you suggest and report back 

 

[SPECIAL LOCATION]

In principal there is no reason why any timer switch shouldn't work correctly via an RCD..

BUT some points for consideration:-

It is possible to trigger some RCD's if the off/on switching action of certain types of loads is not a nice clean operation...

Some RCD's can be over-sensitive and operate when they shouldn't.   (with an appropriate test meter you can actual measure the tripping current & times to verify your RCD is operating correctly)..

Some appliances can have an element of "natural leakage". How old is your pump.. if its getting on a bit and it has some relatively high leakage, that combined with a poor quality timer switch could be causing problems..

Is the timer a basic mechanically operated one, (as you said you needed to reset the time after losing the power), with a simple micro switch operation ?

i.e. one where you push little levers in/out to set the on/off times?

If it is a more modern digital one that has its own internal battery to retain the time and electronics to operate the switching relay may work better..

e.g.  something like one of these type of timers:-

https://www.toolstation.com/axiom-7-day-electronic-lighting-timer-16a-8a/p28896

If you have two RCD's in circuit..  one at your consumer unit plus the RCD socket,

depending upon their operating times it can be an element of pot luck which one operates..

It is possible that if you take the RCD socket out of circuit..

The same timer, (if that is a cause),  could trip the Consumer unit RCD instead!

As has been said a modern correctly wired property would have RCD protection already included at the fuse box to protect socket outlets..

So a socket outlets with RCD protection are generally not required.

Guinness  

 

[hasti]

Hi all,

After a bit of testing and experimenting, I replaced my outdoor RCD socket with a non-RCD socket - and everything is working perfectly!

At some point I will change the manual timer switch with a digital one with a battery back-up, to save having to reset it every time I cut the power.

Thanks, everyone for your helpful advice.

Locked to prevent hi jacking (again)