Motors - hdbk109220040105

DOE-HDBK-1092-2004

6.3.2.4 MOTORS

Elevator and escalator motors are considered as intermittent duty. This allows them to be

protected by the overcurrent protection device supplying the power for the branch circuit, which

is selected by the percentages in NEC Table 430.22 times the full load current of the motors.

For example: What is the load for a 15-minute rated 40-hp, 460-V, three-phase motor used as a

freight elevator motor?

Step 1:

Finding full load current -- NEC Table 430.150

40 HP = 52 A

Step 2:

Finding demand factors -- NEC Table 430.22 (a)

15 minute rated = 85%

Step 3:

Calculating load

52 A x 85% = 44.2A

Answer: Load is 44.2 amps.

6.3.2.5 GROUNDING

All metal raceways and cables, Types MC, Ml, or AC, shall be bonded to the metal frame of the

car. All elevator equipment including metal enclosures for electric devices on the car shall be

grounded in accordance with NEC Article 250.

6.3.2.6 OVERSPEED PROTECTION

Overspeed protection for overhauling and under-hauling is required, as are motor-generator

overspeed requirements that must comply with NEC 430.89, Speed Limitation. However, these

requirements are a part of the more extensive requirements of ANSI/ASME A17.1 for electrical

safety devices, which require scrutiny by designers, maintenance personnel, and inspectors.

6.3.3

EMERGENCY POWER

Emergency power requirements are governed by ANSI/ASME A17.1 Rule 211.2, which requires

that the regenerative power of an overhauling elevator prevent the elevator from attaining the

lesser of the governor tripping speed or 125 percent of the rated speed. If the elevator power

system cannot absorb this power, a load shall be provided on the load side of the elevator

power disconnect switch. If an emergency power supply is designed to operate only one

elevator at a time, the energy absorption means may, if required, be located on the line side of

the disconnect. Other building loads that may be supplied by the emergency power source may

not be considered as absorbing regenerated energy unless they use the emergency power

source as normal power. Refer to Article 620, Part X, of the NEC, Overspeed, for the installation

requirements covering these requirements.

6.3.4

DESIGN

In addition to the NEC, elevator and escalator requirements, there are numerous electrical

requirements for the facilities designer in ANSI/ASME A17.1 and A17.3. A17.1 is a required

reference for new elevator and escalator installations and can be used by the designer in

checking submittal drawings from the manufacturer. ANSI/ASME A17.3 provides the safety

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