trying to use the GSM-Auto switch to remotely turn on my airplane's heater. How do I wire the relays: just like a normal switch
- hot in on one side, hot out on the other?
There is a wiring diagram on the instructions for the switch (at
their website). But you would wire the line in (hot) to the Common terminal of one of the relays and the load out to the NO
(normally open) terminal. Be sure not to overload the power capacity rating of the switch, or you may need to use a step-up
relay to handle the excess load.
I’m upgrading my thermostat
to a WiFi style. The instructions say I need to run a COMMON wire for the new thermostat, but I’m confused about where
to find one.
This is a good question, and asked more and more with
regards to home automation equipment.
Traditionally, thermostats are connected in series with the equipment they control. The low current
requirements of the older style thermostats, allowed them to ‘steal’ power from the circuit they were controlling
with no noticeable effect on the HVAC equipment being turned on and off.
With the advent of home automation, the new ‘smart’ thermostats have
more work to do and consequently draw more power than before. No longer can they steal power from the circuit; they need their
own power source. Typically, this is done by bringing the common wire from the low voltage transformer to the thermostat location.
On a simple 2-wire heat only system where you would have had only a red and white wire, you now would use a third wire for
the common. The next step is to determine which of the low voltage wires on the transformer is being used as a common. This
is accomplished with a small multimeter.
First, set the meter for AC volts. Next, take the red and white wires from the thermostat and twist
them together. This should turn on the heating system. Now, place one meter probe on this connection point (where the wires
are twisted together). The second probe will now be used to find the common wire of the transformer.
Making sure you are on the secondary
(low voltage) side of the transformer, check both wires. One will give you a reading around 0 volts, while the other will
read 24 volts (assuming you have a 24v transformer). The wire that gives you a 24 volt reading is your common wire.
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