(a) Type of Driving Machine. All driving machines shall be of the traction type.

Exception: Winding drum machines may be used for freight elevators subject to the following:

(b) Material and Grooving for Sheaves and Drums. Sheaves and drums used with suspension and compensating ropes shall:

1. (1) Be of metal finished grooves, provided the grooves of sheaves not used to transmit power may be lined with rubber or other sound isolating material.

2. (2) Have a pitch diameter not less than:

   1. (A) 40 times the diameter of the rope, where used with suspension ropes.

      Exception: Existing sheaves where 8x19 wire rope is used and which have a diameter less than 40 diameters of the rope, but not less than 32 diameters, and are provided with permanent marking “Use 8x19 Cables Only.”

   2. (B) 32 times the diameter of the rope, where used for compensating sheaves.

(d) Bolts Transmitting Torque, and Set Screws. Bolts or other means used to transmit torque between the driving sheave and the gearing, and their supports, shall be tightly fitted without play.

Set screws or threaded portions of bolts or screws shall not be used to transmit torque.

(e) Shaft Fillets and Keys. A fillet shall be provided at any point or change in the diameter of driving-machine shafts and sheave shafts to prevent excessive stress concentrations in the shafts.

Shafts which support drums, sheaves, gears, couplings, and other members, and which transmit torque, shall be provided with tight fitting keys.

(h) Driving Machine Brakes.

1. (1) The elevator driving machine shall be equipped with a friction brake applied by a spring or springs, or by gravity, and released electrically.
2. (2) The brake shall be designed and maintained to have a capacity sufficient to hold the car at rest with its rated load.
3. (3) Where gravity is used to apply the brake, the weights shall be guarded to prevent any obstruction being placed under the weights.