I'd like to connect following components:

  1. From the wall socket
  2. .. to a cable
  3. .. to a pressure switch
  4. .. to a transformer
  5. Use the outer wires on the transformer to get 24V (2x12V) to the pump

Question is, how? I've no idea how to actually connect these components. I'm a complete and utter noob and I've no experience whatsoever with these things.

I've made a picture of the components.

First off, the cable is unearthed (should it be?) but there are only two connects (in/out) to the pressure switch, where should the earthed wire go?

Two wires to the in/out on the pressure switch to the transformer - does it matter which one?

From the transformer to the pump, should I put those blue wires together in the same place? Does it matter which ones I connect to what on the pump (+ / -).

I'd appreciate some help!

P.S I dont want to get fried.

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Edit: I need 10 reps to post more than 2 links. Link to the transformer: http://www.electrokit.com/en/transformer-48va-2x12v-2a.45714

Edit: Info on the pressure switch

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  • You should have enough rep now to post more links ;-)
    – yo'
    Jan 10, 2016 at 21:12

1 Answer 1


You're nearly there!


Note: European wire colours used here.

  • Find a suitable enclosure for the transformer, switch and a fuse.
  • Connect the live wire (brown) to the fuse, the fuse to the switch and the switch to one of the 230 V red wires on the transformer primary.
  • Connect the neutral (blue) wire to the red of the transformer primary.
  • Connect the pump to the two outer blue wires on the transformer.
  • Connect the earth / ground wire to the black centre-tap of the transformer.

The result will be a 24 V supply to the pump with what is known as a centre-tap ground. This limits the voltages at the pump to 12 V with respect to ground while still applying 24 V to the motor.

  • A 500 mA fuse would be adequate protection for the setup.
  • Water-proof everything and, if possible, keep the control box remote from any water.


If the pressure switch is exposed or difficult to insulate you may further improve safety by putting the pressure switch in the low-voltage side. This has the disadvantage that the transformer will be always on and wasting a little energy when the pump is not running. (The pressure switch link in your question links to the transformer. Check that it is rated for at least 2 A.)

Version 1 wiring

Version 1 wiring. Note that switch is on mains voltage side of transformer.

Version 2 wiring

Version 2 wiring. Note switch is wired on low-voltage side. Wire switch internally with left cable in nearest terminals to cable entry as shown in the instruction leaflet. Note that there is no switch on the transformer mains side. Unplug when not in use.

  • Superb answer thanks alot. Is it possible to do it without an earthed cable? How do I connect a switch and fuse - are there any online that you can recommend? Thanks
    – Lennart
    Jan 8, 2016 at 8:51
  • I would recommend the earthed cable (and you show one in your photo!) particularly because water is involved. The risk is that at some future date the insulation in the transformer breaks down and the secondary gets connected to live. (1) What country are you in? 230 V looks European. (2) Why avoid the earth connection? (3) Can you fix the link for the pressure switch?
    – Transistor
    Jan 8, 2016 at 9:41
  • I'm in Sweden so that's why 230V. I've no good reason to avoid earthed connection other than easier connection. Post updated with pressure switch!
    – Lennart
    Jan 10, 2016 at 9:41
  • Do you have any examples of a switch and fuse to which I can by an equivalent one here in Sweden/Europe?
    – Lennart
    Jan 10, 2016 at 9:45
  • I don't see the switch link. Can you post it in the comments? I'll look for a fuse. (I'm in Ireland.)
    – Transistor
    Jan 10, 2016 at 10:03

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