Generalaire/Aprilaire 50 Current Sensing Relay

The current sensing relay senses a current when your furnace's blower fan turns on. Simply run the fan wire through the top loop of the relay and when the fan turns on, the relay closes, allowing the 24v power on the relay side to flow through and turn the humidifier on (when humidistat controller also calls for humidity.)

Manufactured by Generalaire

Genuine Aprilaire 24 volt, 0.5 amp current sensing relay. This relay will switch on a 24 vac load (0.5 amp max load) when 4 amps of (blower motor) current is sensed. The pair of wires is 20 awg with a 24" length. Dimensions 2-3/4" wide x 1-7/16" high x 1" thick.

This 24 volt relay is for turning on a 24 vac load such as a humidifier, the 24 vac rating does not refer to the blower voltage. The blower voltage can be 120v or 240v as only the current is sensed. The need to wrap the blower wire around the RP-50 is typical, see instructions.

The Aprilaire 50 current sensing relay is used to turn any humidifier on when the indoor blower of the air handler is energized. The relay makes installing any humidifier easier than ever before. Designed to be installed in series with the 24 volt circuit. Installation instructions included. This relay has a trip on point of 4 amps so if it sees less than 4 amps it will not turn on, if it sees 4 amps or more it will turn on. If you have a load LESS than 4 amps and you still want to use this relay you will need to wrap the wire you are sensing through the metal loop several times. Each time you wrap it through the loop it will add that amperage up. For instance if you have a 2 amp load and you wrap it through 3 times it will see 6 amps and turn on.