Wiring for timer switch

20 Aug 2010
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United Kingdom
I have a switch which powers a small compressor for a Biodigester (waste tank). I have bought a timer that can be wired in but I'm having trouble working out the wiring.

There are three live, 3 neutral and three earth wires.

They are currently wired as follows

2 live into 'L IN'
1 live into 'L OUT'
2 neutral into 'N IN'
1 neutral into 'N OUT'
3 earth into earth

There is a block with four spaces. The diagram for the timer switch shows
1. Live output to appliance

2. Make link with a 1.5 sq mm wire to switch 240Vv AC ONLY. Should you wish to switch other than 240v AC do not use link to terminals 2&3. Feed the required switching voltage to terminal 2 and output from terminal 1.

3. Live from mains

4. Neutral from mains.

My thinking is that the 2 Live (from L IN) should go into 3. The 1 live (from L OUT) should go into 3. The 2 neutral (from N IN) go into 4.

Does anyone have any idea regarding the following
Does the single Neutral go into 2.?
The supply is 240v so should I have a link wire between 2&3.?

Please help....
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Terminal 1 L out.
To save having 3 wires in terminal 3 I would put 1 each of the 'L in' wires to terminals 2 and 3 and then link between the two.

You will have to have all 3 Neutrals in terminal 4 unless you use a seperate connector.
With two wires in the supply side of the switch, it sounds like part of a ring final circuit, or radial circuit feeding other outlets as well.
How is the feed to the pump protected (fused)?

If the switch you wish to replace is an SFCU, holding the fuse that protects the pump and it's wiring, removing that would mean the pump is only protected by the fuse / MCB in your CU. A 30 Amp fuse protecting a 3 Amp circuit is NOT a good idea!

Have you thought about maintenance? If you leave the existing double pole switch in place, and fit your timer on the output from that, when you need to carry out maintenance work on the pump you can isolate it at the switch. Otherwise you would have to isolate the whole circuit, and everything else that circuit feeds.

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