Learn which plants thrive in your Hardiness Zone with our new interactive map!

Why Does the Start Capacitor Overheat?

By Andrea Stein
Start capacitors can overheat due to high levels of voltage.
high voltage hardware - isolators and capacitors image by Roman Ivaschenko from Fotolia.com

A start capacitor refers to an electrical capacitor designed to alter current amounts that are sent to windings in an electric motor to create a rotating magnetic field. A start capacitor can overheat and suffer damage due to a number of causes.


Start capacitors work at voltage classifications that typically range from 370 to 440 V (volts). A sudden surge of voltage, called overvoltage, can cause a buildup of pressure in the sealed aluminum that makes up the outer casing of the capacitor, which can lead to overheating damage to the capacitor’s internal parts and possibly cause the capacitor to explode.

Sticking Relay

As relays open and close, electric sparks, called arcs, can cause the contacts to stick together. A sticking relay forces the capacitor to stay in the circuit for a longer period of time. The excess buildup of electricity can ultimately cause the capacitor to overheat.

Compressor Cycling

Compressors, or mechanical devices that compress gas, can run in rapid cycles that may cause a capacitor to overheat. Start capacitors that cycle above 20 starts, or cycles per hour, may be subject to overheating.