If line voltage is low or missing, which is most likely the cause?

• A. Line power is not present
• B. SSR is defective
• C. Input control signal is stuck
• D. There is an anomalous load condition

Answer: (A)

When line voltage is low or missing, the most likely cause is that line power is not present. The line input is the primary power source for the entire system, so if the mains supply is cut, the voltage at the input drops to zero or to a reduced level, causing everything to stall or underperform.

Other faults describe issues that occur after power is already present. An SSR being defective can prevent proper switching but doesn’t usually remove the incoming power. An input control signal being stuck affects the control logic, not the main supply. A problematic load can cause voltage sags under heavy demand, but the symptoms point most directly to the absence or loss of the line power itself.

Check the main power source, breakers or fuses, and the power cord or connection to confirm that line power is indeed present. If power is present but symptoms persist, investigate the SSR and control circuitry separately.