Final answer:
Thermal relay heating elements should be selected based on the motor's FLA and manufacturer's selection chart to ensure correct sizing for safe and efficient operation. House heating efficiency varies based on insulation, with different power requirements expressed in W/°C needed to maintain a stable temperature. This factor influences the duty cycle of heaters regulated by a thermostat.
Step-by-step explanation:
The selection of a thermal relay heating element is dependent upon ensuring it is correctly rated to safely and efficiently protect an electric motor. For this, the correct answer is choice C: From the motor's Full Load Amperage (FLA) and the manufacturer's selection chart. The FLA provides information on how much current the motor draws when it is running at its full designed load. This information along with the manufacturer's selection chart ensures that the heating element is properly sized according to the specific requirements of both the motor and the environment it will operate in. This method does not directly consider under or over voltage (A and B), nor ambient temperature (D), but it's implied that the manufacturer's chart might take into account various operating conditions, including the ambient temperature.
When it comes to house heating efficiency, different houses will require varying amounts of power expressed in watts per degree Celsius (W/°C) to maintain a stable temperature (∆T). A well-insulated house might require 75 W/°C times 20°C, equating to 1,500 W, while a poorly insulated house could require up to 6,000 W. These numbers help predict the behavior of the house's heater, which operates on a duty cycle - turning on and off to regulate the temperature according to a thermostat. Given the rating of the heater, it's possible to anticipate what the duty cycle will be to sustain the right temperature for a given ∆T.