CSLB C-27 Landscaping ContractorHardscape and FeaturesHard
A landscape contractor is installing a low-voltage lighting system. The total wattage of all fixtures connected to a single transformer is 250 watts. The transformer has a maximum capacity of 300 watts. What is the minimum gauge wire (AWG) required for the main cable run from the transformer to the first fixture, assuming a maximum voltage drop of 5% over a 100-foot run?
- A14 AWG
- B12 AWG
- C8 AWG
- D10 AWG
Show answer & explanationAnswer & explanation
Correct answer: D. 10 AWG
To determine the minimum wire gauge, one must calculate the required current (Amps = Watts / Volts, assuming 12V for low-voltage lighting). Then, using a voltage drop calculator or chart for low-voltage systems, consider the wattage, run length, and desired voltage drop (5%). For 250W at 100ft with a 5% drop, 10 AWG is typically the smallest acceptable wire, while 8 AWG would provide even better performance.
Why the other options are wrong
- A. 14 AWG is too small for 250W over 100 feet and would result in excessive voltage drop.
- B. 12 AWG is generally insufficient for this wattage and distance, leading to more than 5% voltage drop.
- C. 8 AWG would also work and provide less voltage drop, but the question asks for the *minimum* required.
Low-Voltage Lighting Wire Sizing
Wire sizing for low-voltage lighting systems is critical to prevent excessive voltage drop, which can lead to dimmer lights and premature lamp failure. It depends on total wattage, run length, and desired voltage drop percentage.
- Voltage drop calculations are essential for low-voltage lighting.
- Key factors: wattage, distance, and desired voltage drop.
- Larger AWG numbers mean thinner wire; smaller AWG numbers mean thicker wire.
Memory trick: Watt-age, Length, Drop: The Holy Trinity of Wire Sizing.