The 500802 Sensor wire adds floor sensing capability to the P-3285 DualTemp Thermostat (Patio Heating Only). It is a 10K thermistor design and is 10’ Ft long.
No Sensor is included with the P-3285 thermostat - you must purchase this sensor wire to use the P-3285 Thermostat for Patio heating.
Some customers order an extra sensor for 'peace of mind'. Although it is extremely rare for a sensor to fail, they think it is a reasonable precaution to install 2 sensor wires and they consider it cheap insurance.
If you choose to purchase 2 sensors, run both sensors from the Thermostat box to the floor below and then place them between the heating elements 12 inches or more into the heated portion of the floor. You can put them side by side, but connect only one to the thermostat control. If you ever need to replace a faulty sensor, you will have one at your fingertips; simply disconnect one, and connect the back-up.
A spare can come in handy if yours gets lost or damaged during installation.
Each Thermostat Manufacturer uses a different sensor wire.