Section 39.155. Character of switches and disconnectors

(a) Capacity. Switches used as other than disconnectors shall be of suitable voltage and ampere rating for the circuit on which they are installed, and be marked with the current which they are able to safely interrupt. Disconnectors shall be of suitable voltage and ampere rating for the circuit on which they are installed, and shall be marked with warning against opening when carrying load. Where a group of disconnectors is contained in one room or compartment a single conspicuous sign may be sufficient.

(b) Locking. Remotely controlled switches, oil switches and disconnectors shall be arranged so that they may be secured or blocked in the open position and plainly tagged to prevent careless closing while work is being done on equipment controlled by them, unless the switches are so constructed or installed as to prevent accidental closing or live or moving parts of the equipment they control are so guarded as to render blocking and tagging unnecessary. If the accidental opening of a switch or disconnector might cause hazard, similar arrangements should be used for retaining them in closed position. Locking should be used rather than blocking wherever parts of equipment are remote from the point of control. Locking or securing doors of compartments is a means of securing switches in the open position to prevent careless closing while work is being done on the equipment controlled. Blocking the jaws of knife switches is also a method.

(c) Air brake. Unless a switch operating on a circuit above 750 volts makes an air break, there shall be installed between it and the source of energy supply a suitable air or oil break disconnector or equivalent device having an air or oil gap suitable for the operating voltage of the circuit. Reference should also be made to § 39.358 (relating to protecting workmen by disconnectors).

(d) Alignment. Knife switches shall maintain such alignment under service conditions that it may be possible to close them with a single unhesitating motion.