Installation Guide

Combination Starter Construction Types Motor Control Solutions

Construction Type Selection

Panel designers may choose any of the six construction types for their motor control

panel with each construction type offering different advantages.

Construction Types A through D all utilize the same motor controllers and overload

relays. However, they feature different methods to perform disconnect and branch

circuit protection functions:

• Construction Type A is the only construction type that features fuses.

• Type B, which uses an UL 508 motor short circuit protector, is no longer

commercially available.

• Type C utilizes UL 489 inverse time circuit breakers.

• Type D utilizes UL 489 instantaneous trip circuit breakers.

The key distinction between Type A and Type C or D can be simplified to the

selection of a circuit breaker or a fuse for branch circuit protection. A fuse is an

overcurrent protection with a circuit opening fusible part that is heated and severed

by the passage of overcurrent through it. A circuit breaker is a device designed to

open and close a circuit by non-automatic means and to open the circuit

automatically on a predetermined overcurrent without damage to itself when

properly applied within its rating. The key difference between a fuse and a circuit

breaker is that a fuse must be replaced once it experiences an overcurrent

condition while a circuit breaker is resettable. Additionally, fuses operate

independently on each phase while circuit breakers have three-phase common trip.

Construction Type E self-protected combination controllers and Type F

combination controllers both offer the following advantages for panel designers:

• Higher coordinated short-circuit withstand ratings on UL 508A panels

• Easier component selection to meet the requirements of group motor

applications

• Reduced panel space by reducing the number of components

• Required product markings to help designers quickly and accurately select

components

• Increased productivity by reducing the number of wiring connections

UL 508 Type E self-protected combination starters also offer the advantage of

reliability. UL 508's special endurance and short-circuit tests ensure a coordinated

combination starter that will clear a detected fault and protect itself from damage. It

is the only category of combination starter that a designer can easily identify as

self-protected due to the required “Self-Protected Combination Motor Controller”

product marking.

Disconnecting Means on a Feeder or Branch Circuit

The disconnecting means on the feeder circuit, ahead of the last SCPD, must be a

UL 98 disconnect switch or UL 489 circuit breaker. UL 508 switches or motor

protectors are not acceptable.