Final answer:
Branch circuit loads should not exceed 80% of the circuit breaker's capacity, based on safety regulations. This ensures that continuous loads do not result in overheating and potential hazards. Calculations must include all devices on a circuit and consider the 80% rule for safe power usage.
Step-by-step explanation:
For branch circuit loads, you should plan to use no more than 80% of the available current. This safety regulation is in place to prevent overloading a circuit, which could lead to overheating and possibly a fire. For example, a 15-amp circuit breaker should not continuously carry more than 12 amps of current. Using the 80% rule, an appliance with a continuous load, such as a heating appliance, should not exceed 1,400 watts on a 15-amp breaker or 1,920 watts on a 20-amp breaker at 120 volts. While calculating these limits, it is important to consider all devices connected to the circuit.
When multiple appliances are connected in parallel to a single outlet on a 15-amp, 120-V circuit, such as an 1800-W toaster, a 1400-W speaker, and a 75-W lamp, you need to calculate the current drawn by each. If the combined current exceeds the 80% threshold of the breaker's rating, the setup risks tripping the breaker. To calculate power usage over time, like for a house operating at 80% capacity, you would multiply the current by the voltage to get the power in watts, convert it to kilowatt-hours (kWh) for the period of interest, and multiply by the cost per kWh to estimate the electrical expense.