Controls, Sensors, Pumps, and Electrical Interconnections
This domain tests controls, sensors, pumps, and electrical interconnections: how the controller decides to run the pump, where sensors go, and how line-voltage equipment is safely supplied and bonded.
Controller logic and sensors
A differential controller compares collector temperature to storage temperature. Typical settings are pump-on ΔT around 15–20°F and pump-off ΔT around 4–5°F, but follow the manufacturer. The collector sensor must be in a dry well or clamped to the absorber at the hot end; the storage sensor goes low in the tank. Shield sensor cable and keep it separate from line voltage.
Pumps and electrical
Match pump flow and head to the design, and use a relay or controller rated for the pump load. Provide a disconnect within sight, GFCI protection where required, equipment grounding, strain relief, and a properly sized circuit. Bond pool equipment and metallic parts per Article 680; do not confuse bonding with grounding. Add freeze protection: glycol, drainback, or a freeze snap-disc.
Worked example
A controller reads collector 130°F and storage 110°F, ΔT 20°F, so the pump starts. When ΔT falls to 4°F, it stops. If the collector sensor is wrongly placed on the pipe 10 ft from the absorber, the controller sees a delayed, lower temperature and short-cycles.
Traps
Sensor on the wrong end; unshielded cable; no freeze protection; pump relay undersized; no disconnect; bonding omitted at the pool.