What is power factor and why does it matter in industrial electrical systems?

• A. PF = real power / apparent power; indicates how effectively current is used; poor PF increases current, causes higher losses, and can reduce available capacity.
• B. PF = voltage / current; indicates energy efficiency.
• C. PF is the same as efficiency.
• D. PF doesn't matter in AC.

Answer: (C)

Power factor is about how effectively the current in an AC system is being used to do real work. It is the ratio of real power (the actual work you’re getting, measured in watts) to apparent power (the product of voltage and current, measured in volt-amperes). For sinusoidal waveforms, power factor also equals the cosine of the phase angle between voltage and current.

Why this matters in industrial systems is that when there’s a lot of reactive current (from inductive loads like motors and transformers), the current must be higher to deliver the same amount of real power. That extra current leads to greater I²R losses in conductors, more voltage drop along cables, and can push you toward needing larger wiring and equipment ratings. It also increases the apparent power seen by the utility, which can raise demand charges even if you’re not delivering more useful work. Keeping the power factor close to 1 means most of the current is doing real work, which improves efficiency of the electrical system and reduces losses and capacity requirements.

The notion that power factor is the same as efficiency is incorrect. Efficiency is about how much input energy is converted into useful output, taking into account all losses in the device or process. Power factor, by contrast, is about the relationship between voltage and current and how much of that current is actually doing useful work versus circulating as reactive energy. A system can have high efficiency but poor power factor, and vice versa.