Split phase heater - need relay w/dry contact

Devices & Integrations
1

Have a 2 pole wall heater which has port for building management control (BMS).

I have ecobee remote sensor in the room and connected to SmartThings. I can quickly detect occupancy, temp (routine in app) and then heater runs or does not run.

Problem #1: Finding a relay which can be connected to L1 and L2 (no neutral since split-phase).
Problem #2: relay output MUST be dry contact (NO/NC) with 0V. Otherwise will fry the heater board. These will be connected to the heater board BMS input which takes 2 wires. Currently has jumper. [To be crystal - I do NOT need modulating in BMS input of board]

Any help - sincerely appreciated. Zwave or zigbee is fine.

2

What country are you in? Choice may vary by location.

3

USA. East Coast.

4

is there anything? I am checking and finding nothing.

5

I think your “no neutral” requirement is going to be the stumbling block. @JDRoberts any suggestions?

6

You are correct, there are no “no neutral” options for binary relays. Only for dimmers, and for switches which are pretending they are not dimmers. The physics are different.

There is a different way to do this and still meet safety code in most jurisdictions, but it’s complicated, and best Done by a licensed electrician since you can run into quirks during the installation.

So I do think it can be done, but I don’t think it’s a DIY project.

1 Like
7

I am well versed in electrical stuff so probably will understand. The issue I see is the split legs L1, L2. the Asia/EU versions have 1 input for 240 volts.
On neutral - there’s 1 option is to put an isolation transformer and then output of which to ground (which is available). However, am pretty sure won’t be as per code…

8

Likely Won’t be to code and probably won’t work, either. You can’t power a smart device with the same circuit branch You are switching on and off, because then the radio doesn’t have power to hear the next “on“ command from the network. So the neutral is used to power the radio. That option is not typically available from a ground if the device is turned off.

9

There are several options:

  1. Use a Shelly 1 smart relay it has isolated load contacts and is rated for up to 240 volts. See the following but ignore the 12 volt supply.

https://www.reddit.com/r/homeautomation/comments/la4fpm/does_shelly_1_io_circuit_isolated_from_ln/

  1. Use any smart relay rated for up to 240 volts to drive a dumb relay with a 240 volt coil. Connect dry contacts of dumb relay to heater circuit

  2. Use a Zooz Zen 16 which has 3 dry contacts. The Zen 16 can be powered by a USB C power supply or a low voltage door bell or thermostat power supply.

10

Neutral? @Paul_Oliver
Also none of the options you have suggested above take 2 line loads - L1 and L2 and together they make it 240V. There’s only 1 L.

11

Assuming your L1 to L2 voltage is 240 volts or less, you can run a 240 volt smart relay with Line terminal connected to L1 and Neutral terminal connected to L2.

That is how I control my 240 volt baseboard heat at camp.