Specification

Structure of a Motor Starter in Accordance with UL 508A Motor Control Solutions

Group Motor Installations

In a group motor installation, a single disconnecting means and SCPD can be used

for a group of motors. The specific rules are described in NEC Sections 430-112

and 430-53.

Group motor installations are used in the following applications:

• Fractional hp motors—NEC Section 430.53 (A):

For several motors, each rated 1 hp maximum on a branch circuit of 1000 V

maximum, a single SCPD not exceeding 15 A is permitted under the following

circumstances:

— No single motor is rated greater than 6 A.

— The branch-circuit short-circuit device rating marked on any controller is not

exceeded.

— Appropriate motor overload protection is used.

• Smallest rated motor protected—NEC Section 430.53 (B):

The SCPD is sized for the motor in the group with the lowest rating.

• Other group installations—NEC Section 430.53 (C):

Two or more motors of any rating, or one or more motors and other loads,

where all the following conditions are met:

— Each motor controller and overload protection device carries a

Motor Group Installation listing.

— Each circuit breaker (if used) is listed and is of the inverse time type.

— The SCPD (fuse or circuit breaker) is sized for the largest motor plus the

sum of all other motors and loads.

— The sizing of the SCPD (fuse or circuit breaker) does not exceed the

maximum allowed for overload protection of the smallest motor.

— Appropriate overcurrent protection is provided for non-motor loads.

Tap Conductor Sizing Rules

The tap conductor sizing rules for group motor installations are governed by

NEC Section 430.53 (D). Conductors from the load side of the SCPD for the motor

group must comply with one of the following:

• The ampacity is not less than that of the branch circuit conductors.

• The ampacity is not less than 1/3 of the branch circuit conductors, and the

length from the point of the tap to the motor overload device is not more than

7.5 m (25 ft).

• The ampacity is not less than 1/10 of the SCPD for the motor group, the length

from the point of the tap to the controller(s) is not more than 3 m (10 ft), and the

manual motor controller is marked “Suitable for Tap Conductor Protection in

Group Installations.”

NOTE: Products certified for motor grouping must carry the markings on the

product label or instruction sheet required by NEC and UL (such as “Suitable for

Tap Conductor Protection in Group Installations”).

For more information, see data bulletin 8502DB0701 entitled “Group Motor

Installations: Understanding NEC 430.53 Requirements.”