CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A residential client is planning to install a new electric vehicle charger. The charger is rated at 240V, 40A. The existing service is a 200A, 120/240V single-phase dwelling service. The main service panel is located 75 feet from the proposed EV charger location. What is the minimum size copper conductor required for this circuit to limit voltage drop to approximately 3%?
- A8 AWG
- B2 AWG
- C6 AWG
- D4 AWG
Show answer & explanationAnswer & explanation
Correct answer: C. 6 AWG
To limit voltage drop to approximately 3% for a 240V, 40A circuit over 75 feet, a 6 AWG copper conductor is required. This calculation considers the conductor's circular mil area and the allowable voltage drop.
Why the other options are wrong
- A. 8 AWG copper would result in a voltage drop exceeding 3% for this circuit length and current.
- B. 2 AWG copper is significantly oversized, resulting in excessive material and installation costs without significant benefit.
- D. 4 AWG copper is oversized for this application, leading to unnecessary material costs.
Voltage Drop Calculation
Voltage drop is the reduction in electrical potential along the length of a conductor due to its resistance, which can impact equipment performance and efficiency.
- NEC generally recommends a maximum of 3% voltage drop for branch circuits.
- Factors affecting voltage drop include conductor material, size, length, and current.
- Calculations involve conductor resistance (k-factor) and circular mil area.
Memory trick: Don't let the 'Drop' in voltage 'Size' down your circuit's 'Performance'.