Load calculations for circuits supplying lighting units with ballasts are based upon?
a. the total wattage of all lamps in the fixtures b. the circuit voltage times lamp wattage c. the ampere ratings of the ballasts d. 180va per ballast
The correct answer and explanation is:
The correct answer is a. the total wattage of all lamps in the fixtures.
When calculating the load for circuits supplying lighting units with ballasts, the focus is primarily on the total wattage of the lamps installed in the fixtures. This is because the ballasts are responsible for regulating the current to the lamps, but the total electrical load is determined by the power consumption of the lamps themselves.
Here’s why the total wattage of the lamps is the key consideration:
- Lamp Wattage Determines Power Demand: Each lamp has a specific power rating, typically given in watts. When multiple lamps are installed in a fixture, the total wattage is simply the sum of the wattages of all lamps. This total wattage gives a direct indication of how much electrical power the lighting system will consume. Therefore, it forms the basis for calculating the total load on the circuit.
- Ballasts and Lamp Compatibility: The ballast, which is essential for controlling the current and voltage supplied to the lamps, is designed to match the lamp’s requirements. While the ballast does consume some power, its primary function is to ensure that the lamps operate correctly, and it generally does not add a significant load in the way that the lamps themselves do. Therefore, the load calculation focuses on the lamps’ wattage.
- Circuit Design: When designing circuits for lighting, especially those with ballasts, the total wattage of the lamps is used to size the circuit wiring and overcurrent protection devices (like circuit breakers or fuses). This ensures that the circuit can safely handle the electrical demand from the lamps.
- Efficiency Considerations: Ballasts can vary in efficiency, but for load calculation purposes, it’s the lamp wattage that directly determines how much current will be drawn from the circuit.
Thus, the total wattage of all lamps in the fixtures is the correct basis for load calculations in such circuits.