Article 460

Capacitors

Scope. This article covers the installation of capacitors on electrical circuits.Surge capacitors or capacitors included as a component part of other apparatus and conforming with the requirements of such apparatus are excluded from these requirements.This article also covers the installation of capacitors in hazardous (classified) locations as modified by Articles 501 through 503.
Enclosing and Guarding.

Containing More Than 11 L (3 gal) of Flammable Liquid. Capacitors containing more than 11 L (3 gal) of flammable liquid shall be enclosed in vaults or outdoor fenced enclosures complying with Article 110, Part III. This limit shall apply to any single unit in an installation of capacitors.
Accidental Contact. Where capacitors are accessible to unauthorized and unqualified persons, they shall be enclosed, located, or guarded so that persons cannot come into acciden‐ tal contact or bring conducting materials into accidental

contact with exposed energized parts, terminals, or buses asso‐ ciated with them. However, no additional guarding is required for enclosures accessible only to authorized and qualified persons.

Part I. 1000 Volts, Nominal, and Under

460.6 Discharge of Stored Energy. Capacitors shall be provi‐ ded with a means of discharging stored energy.

Time of Discharge. The residual voltage of a capacitor shall be reduced to 50 volts, nominal, or less within 1 minute after the capacitor is disconnected from the source of supply.
Means of Discharge. The discharge circuit shall be either permanently connected to the terminals of the capacitor or capacitor bank or provided with automatic means of connect‐ ing it to the terminals of the capacitor bank on removal of volt‐ age from the line. Manual means of switching or connecting the discharge circuit shall not be used.

Conductors.
1. Ampacity. The ampacity of capacitor circuit conductors shall not be less than 135 percent of the rated current of the capacitor. The ampacity of conductors that connect a capacitor to the terminals of a motor or to motor circuit conductors shall not be less than one-third the ampacity of the motor circuit conductors and in no case less than 135 percent of the rated current of the capacitor.
2. Overcurrent Protection. An overcurrent device shall be provided in each ungrounded conductor for each capacitor bank. The rating or setting of the overcurrent device shall be as low as practicable.Exception: A separate overcurrent device shall not be required for a capacitor connected on the load side of a motor overload protective device.
3. Disconnecting Means. A disconnecting means shall be provided in each ungrounded conductor for each capacitor bank and shall meet the following requirements:
1. The disconnecting means shall open all ungrounded conductors simultaneously.
2. The disconnecting means shall be permitted to discon‐ nect the capacitor from the line as a regular operating procedure.
3. The rating of the disconnecting means shall not be less than 135 percent of the rated current of the capacitor.
Exception: A separate disconnecting means shall not be required where a capacitor is connected on the load side of a motor controller.
Rating or Setting of Motor Overload Device. Where a motor installation includes a capacitor connected on the load side of the motor overload device, the rating or setting of the motor overload device shall be based on the improved power factor of the motor circuit.The effect of the capacitor shall be disregarded in determin‐ ing the motor circuit conductor rating in accordance with 430.22.
Grounding. Capacitor cases shall be connected to the equipment grounding conductor.

460.12 ARTICLE 470 — RESISTORS AND REACTORS

Exception: Capacitor cases shall not be connected to the equipment grounding conductor where the capacitor units are supported on a structure designed to operate at other than ground potential.

460.12 Marking. Each capacitor shall be provided with a nameplate giving the name of the manufacturer, rated voltage, frequency, kilovar or amperes, number of phases, and, if filled with a combustible liquid, the volume of liquid. Where filled with a nonflammable liquid, the nameplate shall so state. The nameplate shall also indicate whether a capacitor has a discharge device inside the case.

Part II. Over 1000 Volts, Nominal

Switching.
1. Load Current. Group-operated switches shall be used for capacitor switching and shall be capable of the following:
  1. Carrying continuously not less than 135 percent of the rated current of the capacitor installation
  2. Interrupting the maximum continuous load current of each capacitor, capacitor bank, or capacitor installation that will be switched as a unit
  3. Withstanding the maximum inrush current, including contributions from adjacent capacitor installations
  4. Carrying currents due to faults on capacitor side of switch
2. Isolation.
  1. General. A means shall be installed to isolate from all sources of voltage each capacitor, capacitor bank, or capacitor installation that will be removed from service as a unit. The isolating means shall provide a visible gap in the electrical circuit adequate for the operating voltage.
  2. Isolating or Disconnecting Switches with No Interrupting Rating. Isolating or disconnecting switches (with no interrupt‐ ing rating) shall be interlocked with the load-interrupting device or shall be provided with prominently displayed caution signs in accordance with 490.22 to prevent switching load current.
3. Additional Requirements for Series Capacitors. The proper switching sequence shall be ensured by use of one of the following:
1. Mechanically sequenced isolating and bypass switches
2. Interlocks
3. Switching procedure prominently displayed at the switch‐ ing location
Overcurrent Protection.
1. Provided to Detect and Interrupt Fault Current. A means shall be provided to detect and interrupt fault current likely to cause dangerous pressure within an individual capacitor.
2. Single Pole or Multipole Devices. Single-pole or multi‐ pole devices shall be permitted for this purpose.
3. Protected Individually or in Groups. Capacitors shall be permitted to be protected individually or in groups.
4. Protective Devices Rated or Adjusted. Protective devices for capacitors or capacitor equipment shall be rated or adjus‐ ted to operate within the limits of the safe zone for individual capacitors. If the protective devices are rated or adjusted to operate within the limits for Zone 1 or Zone 2, the capacitors shall be enclosed or isolated.
In no event shall the rating or adjustment of the protective devices exceed the maximum limit of Zone 2.Informational Note: For definitions of Safe Zone, Zone 1, andZone 2, see ANSI/IEEE 18-1992, Shunt Power Capacitors.
Identification. Each capacitor shall be provided with a permanent nameplate giving the manufacturer’s name, rated voltage, frequency, kilovar or amperes, number of phases, and the volume of liquid identified as flammable, if such is the case.
Grounding. Capacitor cases shall be connected to the equipment grounding conductor. If the capacitor neutral point is connected to a grounding electrode conductor, the connec‐ tion shall be made in accordance with Part III of Article 250.Exception: Capacitor cases shall not be connected to the equipment grounding conductor where the capacitor units are supported on a structure designed to operate at other than ground potential.
Means for Discharge.

Means to Reduce the Residual Voltage. A means shall be provided to reduce the residual voltage of a capacitor to 50 volts or less within 5 minutes after the capacitor is discon‐ nected from the source of supply.
Connection to Terminals. A discharge circuit shall be either permanently connected to the terminals of the capacitor or provided with automatic means of connecting it to the terminals of the capacitor bank after disconnection of the capacitor from the source of supply. The windings of motors, transformers, or other equipment directly connected to capaci‐ tors without a switch or overcurrent device interposed shall meet the requirements of 460.28(A).

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