Power factor
Definition. Power factor is the ratio of real power doing useful work to the apparent power actually drawn from the network, and where it falls below the notified minimum a penalty is added to commercial and industrial bills.
Also called: PF · Power factor penalty · Cos φ
Where you see it: As a decimal figure on demand-metered bills, with a penalty line where it falls below the threshold.
Why motors cause it
Induction motors, transformers and fluorescent ballasts draw magnetising current that does no useful work but still has to be carried by the network. That is reactive power, and it is what drags power factor below unity.
A lightly loaded motor is worse than a fully loaded one. An oversized motor running at a quarter of its rating is a classic cause of a poor site-wide figure.
The penalty
Tariffs specify a minimum power factor, commonly 0.90. Below it, a penalty is applied as a percentage of the bill that scales with how far short you fall.
It is one of the few charges on a Pakistani bill that a consumer can eliminate entirely through their own equipment, which is why it is the first thing an energy audit looks at.
Capacitor banks and payback
A correctly sized capacitor bank supplies the reactive component locally so it is not drawn from the network. Automatic banks switch stages in and out as load varies, which matters on sites whose load changes through the day.
Payback on a site that is regularly penalised is usually measured in months, not years. Oversizing is a real risk though: over-correction causes its own problems and some tariffs penalise leading power factor too.
Frequently asked questions
Can poor power factor affect a domestic bill?
Domestic energy meters record real power, so a household is not billed for reactive power and no penalty applies. It is a commercial and industrial issue.
Does correcting power factor reduce my units?
Only marginally, through reduced losses in your own cabling. The saving is in the penalty and in the recorded kVA demand, not in kWh consumed.
Related terms
- kVA versus kW — Why generators and UPS units are rated in kVA but appliances in watts, and how to size equipment correctly for a Pakistani installation.
- Maximum demand indicator — Why commercial and industrial bills charge for a single half hour of the month, how MDI is measured, and the practical ways to bring the recorded peak down.
- Sanctioned load — The difference between connected and sanctioned load, what happens when you exceed the sanctioned figure, and how to apply to change it in either direction.
Go further
Back to the full 44-term glossary, or open your own bill with the reference number lookup.