8536DB0901R03/21

Combination Starter Construction Types

Combination Motor Controllers

A combination motor controller is a combination of devices that collectively possess the four required functions in a branch circuit for a motor load as defined by the NEC. A combination motor controller can be built using different component constructions, but must possess the essential four functions.

Combination motor controllers can consist of an open assembly or an enclosed assembly. Some combination motor controllers may be assembled in the field using components, while others may be required to be pre-assembled at the factory, depending on the combination construction type or the product.

Some combination construction types, but not all, are required by the NEC to be a listed combination. The UL 60947 standard governs the definition and approval requirements for combination motor controllers. See Table 3 to see which construction types the NEC requires to be listed.

When applying a listed combination motor controller, the components must be applied as stated in the listing, including specific part numbers and all conditions of acceptability.

Combination motor controllers listed to UL 60947-4-1 (formerly UL 508) can be located on the UL website at https://industries.ul.com/industrial-systems-and-components/industrial-control-products-and-systems/short-circuit-current-ratings-for-combination-motor-controller-components.

Combination motor controllers can be constructed using different short-circuit protection methods. Table 3 defines the various construction types, and identifies the construction types that are required by the NEC to be a listed combination.

UL Combination Starter Type Designations

 

UL Combination Starter Type

Device Used for Component Function

Disconnect

Branch Circuit Protection

Motor Controller

Motor Overload Relay

 

Traditional Combination Starters from the 1980s and Earlier

A

UL 98 Manual Disconnect

UL 248 Fuses

UL 60947 Magnetic or Solid-State Controller

UL 60947 Motor Overload Relay

C

UL 489 Inverse Time Circuit Breaker

D*

UL 489 Instantaneous Trip Circuit Breaker

(Motor Circuit Protector)

Introduced 1990

E*

UL 60947 Self-Protected Combination Controller

Introduced 2002

F*

UL 60947 Manual Self-Protected Combination Controller

UL 60947 Magnetic or Solid-State Controller

UL 60947 Manual Self-Protected Combination Controller

Type A and C Construction

Types A and C combination motor controllers are traditional style starters that use either a listed disconnect switch and fuses or a listed circuit breaker as the disconnect means and short-circuit protection. Each type uses a separate UL 60947-4-1 (UL 508) listed motor controller and overload relay. These starters are evaluated by UL under the same set of short-circuit performance tests. Each type of combination starter clears detected faults without causing a fire or posing a risk of an electrical shock hazard to personnel. Each type is allowed to sustain damage that is contained within enclosures and may require the repair or replacement of devices after performing their protective function.

Branch circuits using fuses or circuit breakers are not required to be a part of a listed combination by the NEC. Thus design engineers may elect to apply circuit breakers, fuses, contactors, and overload relays based on their component UL ratings to build a branch circuit. However, a combination motor controller listing may be advantageous for customers to achieve a higher short-circuit current rating.

Circuit breakers offer an advantage over fuses in that they are resettable, and open all three phases during an overcurrent event.

Type D Construction

Type D combination motor controllers use a UL recognized instantaneous trip circuit breaker (also known as a motor circuit protector) as the means of disconnect and short-circuit protection. Motor circuit protectors differ from circuit breakers in that they are often magnetic only, and often include a dial to adjust the motor inrush sensitivity. Because motor circuit protectors do not possess the thermal overload protection, they must be properly paired with a motor starter. Thus the NEC requires that a branch circuit using a motor circuit protector must be applied per the same requirements as a listed combination motor controller.

Type D combination motor controllers are often used in applications where the motor may be a standard type or a high efficiency type, because the motor circuit protector provides adjustment ability for the inrush sensitivity.

The NEC requires that the motor circuit protector inrush setting be no more than 800% for standard motors or 1100% for high efficiency motors. If a motor trip occurs during start up, then the NEC allows the inrush setting to be set as high as 1300% for standard motors or 1700% for high efficiency motors. This requirement does not apply when the motor FLA is 8 amperes or less and when the continuous current rating of the motor circuit protector is 15 amperes or less.

When selecting a Type D combination motor controller, do not assume the prescribed motor circuit protector has the required motor inrush setting range required for code compliancy. Always verify that the inrush dial setting range is compliant for the application.

Type E Construction

The concept of a self-protected combination starter was introduced from Europe during the 1980s. This concept unveiled an integrated device that performed all the required functions of a combination motor controller in a single component.

The first self-protected combination starters were manual, but by the mid-1980s, electromechanical self-protected combination starters were also on the market. These starters cleared detected faults within their rating without sustaining damage and could be put back into operation.

UL introduced this concept in 1990 and added the Type E self-protected category for both manual and electromechanical combination starters. UL added a separate set of short-circuit and endurance performance tests just for the Type E self-protected category.

Type E combination motor controllers possess an advantage over the other construction types in that the combination motor controller must be able to be put back into operation after a short-circuit. Other construction types do not necessarily guarantee that the contactor or overload relay will not sustain any damage during a short circuit, and maintenance may be required to resume operation.

Type F Construction

Many Type E combination motor controllers are manually operated and require the addition of a contactor to permit signals from remote devices or a PLC to start or stop a motor. However, UL component ratings of contactors do not specify protection requirements using a Type E combination motor controller; rather, they only specify protection requirements using a circuit breaker or fuse. Thus UL addressed this by recognizing a Type F category in 2002. This combination consists of a self-protected combination motor controller and a contactor.

Type F combination motor controllers are advantageous in that they require less space compared to traditional constructions, while having a high short-circuit current rating.

Self-Protected Designation and Implications

A combination starter must pass certain performance tests specified by UL 60947-4-1 (formerly UL 508) before it can be designated as self-protected. The required test sequence for the Type E self-protected combination starters is listed in UL 60947-4-1, Table DVC.4.2.1.1.5. The test sequence includes both high fault and interrupting ability short-circuit (low fault) detection tests, followed by an endurance test.

The tests required for Types A through D and Type F combination starters are listed in UL 60947-4-1, Table DVC.4.2.1.1.4. This test sequence does not include the detection of low fault short-circuit tests followed by the endurance test. This is the difference between the testing and performance of a Type E self-protected combination starter and the other starter types.

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 use the same motor controllers and overload relays. However, they feature different methods of performing disconnect and branch circuit protection functions:

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

  • Type B, which uses a UL 60947-4-1 (formerly UL 508) motor short-circuit protector, is no longer commercially available.

  • Type C uses UL 489 inverse time circuit breakers.

  • Type D uses UL 489 instantaneous trip circuit breakers.

The key distinction between Type A and Types C or D is whether a circuit breaker or fuse is used for branch circuit protection. A fuse is an overcurrent protection device 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 60947-4-1 Type E self-protected combination starters also offer the advantage of reliability. UL 60947-4-1’s special endurance and short-circuit tests help 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.

Motor Starter Line Diagrams

Power Supply Circuit

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