Article 110 Requirements for Electrical Installations

I. General

Only approved equipment and conductors are acceptable.

The Code lists considerations for the examination of equipment such as mechanical strength, electrical insulation, etc.

Copper is to be used unless otherwise specified. Sizes given are for copper unless otherwise specified.

The entire electrical circuit, including all devices and wire, must be chosen and coordinated so that a fault will be cleared before extensive damage takes place.

II. 600 Volts, Nominal, or Less

(A) Clearances for three conditions are noted. Condition 1 consists of live exposed parts on one side and no live or grounded parts on the other side of the working space or guarded live parts (wood or other insulating material used) on both sides of the working space. Condition 2 consists of exposed live parts on one side and grounded parts on the other side. Condition 3 consists of exposed live parts on both sides. For voltages to ground between 0 and 150 V, a minimum clear distance of 900 mm (3 ft.) is required in all cases. For voltages to ground between 151 and 600 V, Condition 1 requires 900 mm (3 ft.) clearance. Condition 2 requires 1.1 m (3½ ft.), and Condition 3 requires 1.2 m (4 ft.). No working space is required behind assemblies where no renewable parts are on the back and all wiring is accessible from the front (such as panelboards). A minimum of 762 mm (30 in.) in width is required in front of electrical equipment as well as room for a 90° opening of doors. There are requirements in the Code when the voltage is not greater than 30 volts rms, 42 volts peak, or 60 volts dc. There are also requirements in existing buildings where equipment is being replaced.

(E) Headroom of 2 m (6½ ft.) is required above service equipment, motor control centers, panelboards, or switchboards, with the exception of dwelling units not in excess of 200 A. If the equipment exceeds 2 m (6½ ft.), headroom shall be at least the height of the equipment.

III. Over 600 Volts, Nominal

IV. Tunnel Installations Over 600 Volts, Nominal

V. Manholes and Other Electric Enclosures Intended for Personnel, All Voltages