Switches

Single-throw knife switches must be placed so that gravity will not tend to close them. Single-throw knife switches approved for use in the inverted position must be provided with a locking device that will ensure that the blades remain in the open position when so set.

Double-throw knife switches may be mounted so that the throw will be either vertical or horizontal. If the throw is vertical, a locking device must be provided to ensure that the blades remain in the open position when so set.

Connection of Switches

Single-throw knife switches and switches with butt contacts must be connected so that the blades are de-energized when the switch is in the open position.

Single-throw knife switches, molded-case switches, switches with butt contacts, and circuit breakers used as switches must be connected so that the terminals supplying the load are de-energized when the switch is in the open position.

Grounding

Snap switches, including dimmer switches, must be effectively grounded and must provide a means to ground metal faceplates, whether or not a metal faceplate is installed.

Regulations pertaining to switchboards and panelboards are set out in 29 CFR 1910.305.

Enclosures for Wet or Damp Locations

Enclosures in damp or wet locations must be installed such that moisture cannot enter and accumulate. There must be at least one-fourth inch of airspace between the enclosure and the supporting surface. The enclosures must be weatherproof in wet locations.

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