Override switch for Timer

[SJA79]

Hi,

I've been asked to provide an override switch remotely for some external lighting which is on a din rail Timer so they would like to if required, to turn lights off if Timer is in operation and vice versa turn lights on if Timer is off. Would a 3 position switch like this do the trick and negate the need for a relay? 20 Amp SP 2 Way and Off Grid Switch - https://www.tlc-direct.co.uk/Products/MKK4899.html There will be 3c from the Timer to switch and 3c from switch to lights.

Thanks and any other suggestions welcome.

 

[SparkyChick]

Providing it is an on/off/on (i.e. position 1 - common -> L1, position 2 - no connection, position 3 - common -> L2 - or equivalent), then yes you can do it.

Common - Line
L1 - Switched Line -> Switched contact COMMON on timer
L2 - Switched Line -> Switched contact NO on timer

The timer is running permanently. With switch in position 1, the light is controlled by the timer, position 2, it's off and position 3 it's on permanently as the timer is bypassed.

I was about to post saying no it's not possible with a single switch, but it is.

Edit:- Just re-read your post, you can't do it with 3 core from timer->switch and then switch->light.

3 core+e from switch->timer and then onto the light is possible, but you're a core short in the cable from the timer because you need a neutral to go on to the light.

 

[SparkyChick]

Re-read the OP just to be sure and I missed the bit about 3c from timer to switch and then 3c from switch to light. Using the on/off/on switch with the cabling as described is not possible because you don't have enough cores in the cable from the timer to the light to include a neutral. It will work if the cabling goes 3c+e from timer to switch and then from timer to light.

If the cabling is already fixed, you need to use two switches. One 2 way and one 1 way (or two 2 ways) connected as shown below.

 

[SJA79]

Hi Sparkychick,

Thanks for the replies.

Apologies I meant I am running in 3c&e earth and doing away with the existing 2c &e. My initial concern was even if they only wanted to override the timer to perm on (and use a normal 1g2w switch) then there would be backfeed to the switched side of the timer which could possibly cause damage to the unit so your answer has confirmed my thinking. As you say a 2g switch in series would also have been an option.

Many thanks for the help, I'll try the 3 position sw and see how it goes.

S

 

[SparkyChick]

Providing the timer is a mechanical switch, and not an electronic device and the contacts are entirely separate from the timer control supply, then you should be fine.