NEC Commercial Electrical Practice Test

For a phase converter supplying variable loads, conductors on the single phase supply must be rated at what percentage of the phase converter nameplate input?

1. 100%

2. 110%

3. 125%

4. 150%

The correct answer is: 125%

In the context of electrical installations involving phase converters, particularly when handling variable loads, the conductors on the single-phase supply must be adequately sized to handle potential overloads while ensuring safety and compliance with the National Electrical Code (NEC). The correct answer indicates that conductors should be rated at 125% of the phase converter's nameplate input. This requirement stems from the need to account for fluctuations in load that might occur in variable load applications. When a phase converter is supplying power, it can draw higher starting currents, especially if the motor load is significant or if there are demand spikes during operation. By sizing the conductors at 125% of the nameplate input, the system allows for safe operation without exceeding the capacity of the conductors under varying load conditions. This practice mitigates the risk of overheating and ensures that the conductors can handle transient currents effectively. Additionally, this adjustable rating helps in future-proofing the installation, providing an additional margin of safety for unexpected load conditions or equipment changes. Choosing a rating lower than 125%, such as 100% or even 110%, would not provide the necessary headroom for the increased current that may occur during operational surges or if the connected load increases over time, leading