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I'm not sure what I'm looking for, but what I need is a relay switch that will control two things, or maybe two different relays are needed, I'm not sure.

Basically, from my Raspberry PI I want to control two things;

  1. An electrical outlet and it's power, with NC side wired, so that my plug is on unless I turn it off from the PI.

Part 1 can I do on my 2 channel relay:

https://www.amazon.com/SainSmart-101-70-100-2-Channel-Relay-Module/dp/B0057OC6D8

I'm having trouble with part 2.

  1. Have another wire interrupted also at the same time the plug is turned off. This wire is it's own power source and will not be powered by the wall electrical line like the plug, I simply want to interrupt the line when off.

Not sure if I need a second relay or something else for this purpose, as I don't want the power from the wall routed to this secondary line.

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  • \$\begingroup\$ (1) "non-electrical wire" doesn't make much sense. You probably mean "non-mains, low-voltage wire". (2) "... so that my plug is on unless I turn it off ...". You should be switching power to a socket with shrouded contacts. Switching power to a plug could result in live protruding pins. \$\endgroup\$
    – Transistor
    Nov 20, 2017 at 18:58
  • \$\begingroup\$ @Transistor Could be plastic fence wire, no idea how or why you would need to switch it though.. Maybe plastic transistors? \$\endgroup\$
    – Trevor_G
    Nov 20, 2017 at 19:19

3 Answers 3

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schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Two options.

Figure 1 shows the wiring of the relay options suggested in the other answers. Since you already have two single-pole relays (b) is the simple option for you. You just need to switch the coils of both relays at the same time.

  • RLY2 is wired as an NC, normally closed, circuit. It will disconnect when the relay is energised.
  • RLY3 is wired as a NO, normally opened, circuit. It will connect when the relay is energised.

(b) also has the advantage that there is better isolation and no risk of mains on the DC circuit in the event of catastrophic failure of the relay.

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Use one of the relays on that board to switch the AC outlet, and the other relay to switch the second circuit.

As Trevor sugggests, you could use a double or triple pole relay, but the two single pole relays on your board will work just as well.

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You can use a multiple pole relay, but chose one with sufficient isolation between the poles. Maybe a three pole with the centre pole grounded for some added protection.

enter image description here

If you must use a patch board, the one you mentioned should also work assuming it brings out the normally closed connection. Hard to tell from the amazon information.

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