Capacitors

Article 460 covers capacitors, most often installed to correct power factor on systems with heavy motor loads. It sizes the conductors feeding a capacitor above its rated current because capacitor current runs high, and sets overcurrent and disconnecting requirements.

The signature safety rule is the discharge requirement: a capacitor stores energy and stays charged after the supply is cut, so it must have a means to bleed that charge down to a safe level within a set time after disconnection. Anyone who has grabbed a charged capacitor understands why — the article exists to keep a 'dead' circuit from delivering a dangerous jolt.

When it applies

Article 460 governs power capacitors, usually installed for power-factor correction on motor loads. Beyond sizing the conductors and overcurrent, the headline requirement is a discharge path so the stored charge bleeds off after the power is cut.

Common mistakes

• Sizing capacitor conductors like a normal load and ignoring the higher ampacity multiplier the Code requires for them.
• Skipping or disabling the discharge resistors and leaving a charged capacitor waiting for the next hand.
• Forgetting the discharge time limits, so a technician opens the cabinet too soon.

In the field

I do a lot of commercial power-factor work, and the one thing I drill into anyone near a capacitor bank is that it stays dangerous after the disconnect opens. A big cap can hold a lethal charge with the power off. The Code requires a discharge means for exactly that reason. Kill the power, wait out the discharge time, then verify zero volts before you touch a terminal. Every time.