I. General

490.1 Scope. This article covers the general requirements for equipment operating at more than

600 volts, nominal.
FPN No. 1: See NFPA 70E-2004, Standard for Electrical Safety in the Workplace, for electrical safety requirements for employee workplaces.
FPN No. 2: For further information on hazard signs and labels, see ANSI Z535-4, Product Signs and Safety Labels.

490.2 Definition.

High Voltage. For the purposes of this article, more than 600 volts, nominal.

490.3 Oil-Filled Equipment. Installation of electrical equipment, other than transformers covered in Article

450, containing more than 38 L (10 gal) of flammable oil perunit shall meet the requirements of Parts II and HI of Article 450.

II. Equipment — Specific Provisions

490.21 Circuit-Interrupting Devices. (A) Circuit Breakers.

(1) Location.

(a) Circuit breakers installed indoors shall be mounted either in metal-enclosed units or fire-resistant cell-mounted units, or they shall be permitted to be open-mounted in locations accessible to qualified persons only.

(b) Circuit breakers used to control oil-filled

transformers shall either be located outside the
transformer vault or be capable of operation from
outside the vault.

(c) Oil circuit breakers shall be arranged or located

so that adjacent readily combustible structures or
materials are safeguarded in an approved manner.

(2) Operating Characteristics. Circuit breakers shall have

the following equipment or operating characteristics:

(1) An accessible mechanical or other approved means for manual tripping, independent of control power

(2) Be release free (trip free)

(3) If capable of being opened or closed manually while

energized, main contacts that operate independently of the speed of the manual operation

(4) A mechanical position indicator at the circuit breaker to show the open or closed position of the main contacts

(5) A means of indicating the open and closed position of the breaker at the point(s) from which they may be operated

(3) Nameplate. A circuit breaker shall have a permanent and legible nameplate showing manufacturer's name or trademark, manufacturer's type or identification number, continuous current rating, interrupting rating in megavolt-amperes (MVA) or amperes, and maximum voltage rating. Modification of a circuit breaker affecting its rating(s) shall be accompanied by an appropriate change of nameplate information.

(4) Rating. Circuit breakers shall have the following ratings:

(1) The continuous current rating of a circuit breaker shall not be less than the maximum continuous current through the circuit breaker.

(2) The interrupting rating of a circuit breaker shall not be less than the maximum fault current the circuit breaker will be required to interrupt, including contributions from all connected sources of energy.

(3) The closing rating of a circuit breaker shall not be less than the maximum asymmetrical fault current into which the circuit breaker can be closed.

(4) The momentary rating of a circuit breaker shall not be less than the maximum asymmetrical fault current at the point of installation.

(5) The rated maximum voltage of a circuit breaker shall not be less than the maximum circuit voltage.

(B) Power Fuses and Fuseholders.

(1) Use. Where fuses are used to protect conductors and equipment, a fuse shall be placed in each ungrounded conductor. Two