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My use is for switching guide wires for a Husqvarna Automower setup. I want to have two separate guide wires going through two separate gates. The SPDT will be used to switch between the two guide wires. Unfortunately I am not able to find the voltage and amperage for the guide wire. The only resource I’ve found has indicated ~20V. I want to connect the relay to a zwave outlet to control which guide wire is active. I plan to use a SPDT relay, which I think fits my purpose.

I am open to suggestions.

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  • Can you step back and tell us why you want to use a relay with a 120V coil, and also why you're trying to order electronics bits from Amazon?
    – ThreePhaseEel
    Commented Jul 30, 2023 at 19:51
  • If you "assume hot and ground" for a 120V coil connection, 120VAC is not the voltage you should be working with. Stick to 12V until you learn a lot more, it'll be safer.
    – Ecnerwal
    Commented Jul 30, 2023 at 20:00
  • if that relay catches on fire and burns down your house, then do not expect the insurance company to pay the claim
    – jsotola
    Commented Jul 30, 2023 at 20:03
  • Instead of throwing around model #s...: What is the voltage and current to be switched? How often will it need to be switched? What is the controlling device voltage?
    – manassehkatz-Moving 2 Codidact
    Commented Jul 30, 2023 at 20:15
  • My use is for switching guide wires for a Husqvarna Automower setup. I want to have two separate guide wires going through two separate gates. The SPDT will be used to switch between the two guide wires. Unfortunately I am not able to find the voltage and amperage for the guide wire. The only resource I’ve found has indicated ~20V. I want to connect the relay to a zwave outlet to control which guide wire is active.
    – Sumit
    Commented Jul 30, 2023 at 20:24

1 Answer 1

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STOP. Do not connect AC power to any part of your low-voltage system.

What you're doing in the low-voltage regime is perfectly fine. However, you are choosing a relay with a 120 volt AC coil, which means you're going to be taking AC 120V power and delivering it to the coil somehow. There is no safe way to do that.

Use a relay with a low-voltage coil and supply it with low voltage.

Have all AC power contained inside proper "Class 1" wiring methods and enclosures. Never mix AC mains and low voltage. Here's how you cross that threshold:

How to get low-voltage that is "on" when the AC power is

Since you seem to want the relay to actuate when AC power is available, I'm presuming you are having your low-voltage circuit react to something fed by AC, such as a refrigerator light, garage door opener light, socket on a generator, supply from a time-of-use switch, sump pump limit switch, or what have you. How do we get low voltage from that?

  • If it's a plug, easy peasy - use a "wall wart" power supply or "lump in cord" power supply. I bet you have a drawer full of them. If you like 5 volts, even easier - any USB power supply.
  • If hard-wired, then use a 24V thermostat transformer, or 16-24V doorbell transformer. They mount on a common 99 cent steel junction box knockout or cover, and they are cheap commodities.
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  • Thank you for your answer, I think a 12V “wall wart” power supply is what I need paired with a 12VDC SPDT relay. My use is for switching guide wires for a Husqvarna Automower setup. I want to have two separate guide wires going through two separate gates. The SPDT will be used to switch between the two guide wires. Unfortunately I am not able to find the voltage and amperage for the guide wire. The only resource I’ve found has indicated ~20V. I want to connect the relay to a zwave outlet to control which guide wire is active.
    – Sumit
    Commented Jul 30, 2023 at 20:46

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