ProcirelPower Factor Explained: Why Real Power Is Not Apparent Power
Apparent power (VA) is what the cable carries; real power (W) is what your equipment converts. Power factor is the ratio and when it drifts below ~0. 9, utilities start charging for the privilege of pushing reactive current back and forth.
> At a glance: 7 minute guide · part 2 of 10 in the electrical engineering complete guide track · includes a worked example and a quick-reference table.
## Real, reactive, apparent
Resistive loads draw current in phase with voltage: PF = 1. Motors and inductive ballasts lag the current (PF 0. 7–0. 85 typical), and the extra current delivers no work. The power triangle relates them: S² = P² + Q².
| Q | u | a | n | t | i | t | y | | | | |
| — | — | — | — | — | — | — | — | — | — | — | — |
| S | y | m | b | o | l | | | | | | |
| U | n | i | t | | | | | | | | |
| R | e | l | a | t | i | o | n | s | h | i | p |
| Real power | P | kW | Does the work | | | | | | | | |
| Reactive power | Q | kVAr | Magnetic fields, zero net work | | | | | | | | |
| Apparent power | S | kVA | Cable loading | | | | | | | | |
| Power factor | P/S | | 1.0 ideal | | | | | | | | |
| Capacitor correction | C | kVAr | Cancels Q | | | | | | | | |
## Why it costs money
What this means at the bench: Cables, transformers and switchgear must carry the apparent current. A factory at PF 0. 7 draws 43 % more current than necessary for its real load utilities pass that on as demand charges or direct PF penalties.
## Correction in practice
Capacitor banks counteract lagging inductance, sized in kVAr. Local correction at each large motor is cleanest; central automatic banks handle mixed loads. Overshoot into leading PF is as undesirable as the lag it cured.
## How to apply this in your build
Work through the sequence below each step assumes the previous one passed. For numbers that need calculating, the linked tools at the end of this guide do the arithmetic instantly.
1. Measure or estimate the load’s PF (nameplate or meter)
2. Compute apparent power and excess current
3. Size correction capacitors to lift PF to ~0.95
4. Re-measure after correction under real load
### Worked example
A 20 kW motor installation at PF 0. 75 draws 26. 7 kVA (116 A at 230 V three-phase). Correcting to 0. 95 drops it to 21. 1 kVA (91 A) smaller cables, lower demand charge, cooler switchgear. Run the numbers yourself with the Electrical Power Calculator and the result should agree to within rounding.
> Practical note from the bench. Every industrial audit we publish starts the same way: measure PF at the main panel under normal load before touching a single capacitor.
## Field mistakes we see again and again
– Correcting to exactly 1.0 risk of resonance and leading PF at part load
– Fixing PF at the panel while long runs still carry reactive current
– Ignoring harmonics from VFDs standard capacitors can resonate
## Key takeaways
– Real, reactive, apparent the foundation of this guide; revisit it if any measurement here surprises you.
– Why it costs money the foundation of this guide; revisit it if any measurement here surprises you.
– Correction in practice the foundation of this guide; revisit it if any measurement here surprises you.
## Prerequisites and preparation
Before starting: measure or estimate the load’s pf (nameplate or meter) and compute apparent power and excess current. Keep the [Electrical Power Calculator](/tools/electrical-power) open every number in the worked example is reproducible. Total time including the bench steps: about 6–7 minutes.
## Who benefits most
Hobbyists meeting this topic for the first time, students who want the version with real numbers instead of abstract symbols, and returning engineers refreshing a corner of the craft. The mistake list alone justifies the visit every entry in it was learned the expensive way.
### Quick reference card
| Aspect | Where to find it in this guide |
| — | — |
| Core theory | Real, reactive, apparent |
| Application steps | How to apply this in your build |
| Worked numbers | Worked example |
| Failure modes | Field mistakes we see again and again |
## How this fits the electrical engineering complete guide track
This guide is one stop in the structured learning path. Start from the [electrical engineering complete guide](/tutorial/electrical-engineering-complete-guide) pillar page for the full map, or continue with [single versus three phase](/tutorial/single-phase-vs-three-phase) and [transformer efficiency](/tutorial/transformer-losses-efficiency). For the arithmetic, open the [Electrical Power Calculator](/tools/electrical-power).
## Frequently asked questions
Does power factor matter at home?
Residential meters bill real energy, so mostly it is an efficiency issue; industry feels it directly in demand charges.
What is a good PF target?
0.95 lagging the utility-pleasing sweet spot without overshoot.
Is there a calculator for this?
Yes the [Electrical Power Calculator](/tools/electrical-power) tool runs the formulas from this guide instantly, client-side, with no signup.
## Where to go next
– The complete electrical engineering guide: [Electrical Engineering complete guide](/tutorial/electrical-engineering-complete-guide)
– Read next: [pid controller explained: proportional-integral-derivative in practice](/tutorial/pid-controller-explained)
– Also in this track: [single-phase vs three-phase power: the real differences](/tutorial/single-phase-vs-three-phase)
– Continue with: [transformer types and where each one belongs](/tutorial/transformer-types-applications)
– Calculate as you go: [power calculator](/tools/electrical-power) · [transformer turns ratio tool](/tools/transformer-turns-ratio) · [cable sizing helper](/tools/wire-gauge-awg)
– Bookmark this page against the day a measurement surprises you. Most readers return to the table and the mistake list first, and that is the correct order.
## Bench verification habits
Keep a lab notebook entry for every build in this track: the measured values, the deviations from the guide and the reason for each. Six months from now, those notes are worth more than any tutorial, because they describe your bench and your components rather than a general case.
When a result here disagrees with your expectation, write down both numbers before changing anything. The gap between predicted and measured is where the real engineering lives, and it is usually a tolerance, a parasitic or an assumption that was never checked.
## Formulas and checks from this guide
Verification checklist for this track: isolate before touching, verify with a CAT-rated meter, and re-check protective device ratings after any load change. Mains discipline is a habit, not a step, and every guide here assumes it.
Bookmark this page against your next build in the track: the checklist above is the same one used across 27 guides in this series.
## From our lab notebook
Isolated low-voltage work, yes. Mains and panel work needs a qualified electrician, every time.
Inrush from motors or supplies. Curve C breakers tolerate it, and sizing follows the datasheet.