Capacitor
A component that stores charge for motor starting and power factor correction.
Quick Answer
A capacitor stores electrical charge and releases it, and in building electrical work it appears in motor starting and running circuits, in HVAC equipment and in power factor correction banks. Most are built into equipment, so estimators usually count only the stand-alone banks shown on one-lines, in EA by kvar.
The Full Picture
A capacitor is two conductive plates separated by an insulator. It stores energy in an electric field and gives it back, which makes it useful for shifting the timing between voltage and current. In single-phase motors, run and start capacitors help the motor start and run efficiently, so they are found inside air conditioners, compressors, fans and pumps. In larger electrical systems, capacitor banks supply reactive power to improve power factor, which is the ratio of real power to apparent power.
For an estimator, the practical question is whether the capacitor is a separate item or part of other equipment. Motor and HVAC capacitors are components of the equipment, so they come inside the rooftop unit or compressor and are not counted in the electrical takeoff. A power factor correction bank is different. It appears on the one-line diagram as a named piece of equipment with a kvar rating and a protective device, and on the plans as a location in the electrical room. The specifications under Division 26 describe the bank and its controller.
The takeoff unit is EA for a stand-alone bank, described by kvar and voltage, with the feeder, protective device and mounting carried on other lines. There is no quantity of capacitor LF or SF, so the effect on the estimate comes from related items: the feeder size, the breaker and the space. Safety rules also shape the work. OSHA requires that most capacitors have an automatic means of draining stored charge after they are disconnected, and a visible isolation means for removable capacitor banks above 600 volts.
Capacitors also carry an environmental history. Older capacitors and some other electrical equipment contained PCBs, and federal rules restrict their use: for example, PCBs in large capacitors are limited to certain installations. That is mostly a renovation issue, where removed equipment may require special handling and disposal. An estimator pricing a retrofit should read the hazardous materials survey and the demolition notes before assuming old capacitors can go to ordinary disposal.
Real Examples
Common Misconceptions
People assume: Every capacitor on a job needs its own takeoff line.
Actually: Most capacitors are internal components of motors and HVAC equipment. Only stand-alone banks, such as power factor correction units shown on the one-line, are counted.
People assume: A discharged-looking capacitor is safe to handle.
Actually: Capacitors can hold charge after power is removed, which is why safety rules call for draining means. Treat that as a safety and installation matter and follow the project's procedures.
Frequently Asked Questions
What does a capacitor do in an electrical system?
It stores charge and releases it, which helps start and run single-phase motors and, in banks, improves power factor.
Are capacitors counted in an electrical takeoff?
Only stand-alone ones, such as power factor correction banks on the one-line. Capacitors inside motors and HVAC units come with the equipment.
What is kvar?
Kilovolt-amperes reactive, the unit used to rate how much reactive power a capacitor bank supplies.
Do capacitors need a discharge means?
Generally yes. OSHA's 29 CFR 1910.305(j)(6) requires most capacitors to have a way to drain stored charge once disconnected, with exceptions for surge capacitors and those built into other apparatus.