Capacitors are used in turning circuit in AC. These are non polarized. So as the AC switches direction, it cannot damage the capacitors because the capacitor is simply not polarized and can be plugged in either direction. Electrolytic Capacitors (which are polarized) are used in Smoothing out ripples in DC.
Similarly one may ask, why do electrolytic capacitors have a polarity?
This is due to their construction: the dielectric is a microscopically thin layer of insulation deposited on one of the plates by a DC voltage during manufacture. These are called electrolytic capacitors, and their polarity is clearly marked.
How do you tell the polarity of an electrolytic capacitor?
To determine polarity in CAPACITORS: Electrolytic capacitors are often marked with a stripe. That stripe indicates the NEGATIVE lead. If it's an axial leaded capacitor (leads come out of opposite ends of the capacitor), the stripe may be accompanied by an arrow that points to the negative lead.
Are motor run capacitors polarized?
Start capacitors above 20 µF are always non-polarized aluminium electrolytic capacitors with non solid electrolyte and therefore they are only applicable for the short motor starting time. The motor will not work properly if the centrifugal switch is broken.