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. Used to turn any humidifier on when indoor blower of air handler is energized. The pair of wires is 20 awg with a 24" length. Dimensions 2-3/4" wide x 1-7/16" high x 1" thick. 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. Installation instructions included. Makes installing any humidifier easier than ever before.