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OEM Control Components
Control Circuit Protection
Supplementary Protectors
vs.
Miniature Circuit Breakers
UL 1077 vs. UL 489
OEM Control Components
What is Supplementary Protection?
Supplementary Overcurrent Protective Device –
Definition
A device intended to provide limited overcurrent protection for specific applications
and utilization equipment such as luminaires (lighting fixtures) and appliances (and
other equipment or for internal circuits and components of equipment). This limited
protection is in addition to the protection provided in the required branch circuit by the
branch circuit overcurrent protective device.
NEC2005, NFPA 70: National Electrical Code,
Article 100, Definitions (70-31)
Article 240.10 [Overcurrent Protection] (70-84)
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What is a Final Overcurrent Device?
Circuit Breaker –
Definition
A device designed to open and close a circuit by nonautomatic means and to open the
circuit automatically on a predetermined overcurrent without damage to itself when
properly applied within its rating.
NEC2005, NFPA 70: National Electrical Code,
Article 100, Definitions (70-27)
Circuit Breaker (Final Overcurrent
Device)
Circuit Conductors
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November, 2006
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What is a Branch Circuit?
Branch Circuit –
Definition
The circuit conductors between the final overcurrent device protecting the circuit and
the outlet(s).
NEC2005, NFPA 70: National Electrical Code,
Article 100, Definitions (70-26)
Final Overcurrent Device
Circuit Conductors
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November, 2006
OEM Control Components
What is Supplementary Protection?
Examples
Circuit Breaker
Blender
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Garbage
Disposal
Vacuum
Cleaner
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OEM Control Components
What is Supplementary Protection?
Examples
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Circuit Breaker or Supplementary Protector?
UL 1077: UL Standard for Safety for
Supplementary Protectors for Use in Electrical
Equipment [CSA 22.2 No. 235]
Standards
NFPA 70: National
Electrical Code
UL 489: UL Standard for Safety for Molded-Case
Circuit Breakers, Molded-Case Switches, and
Circuit-Breaker Enclosures
[CSA
22.2 No. 5]
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Circuit Breaker or Supplementary Protector
Standards
UL 489 – These requirements apply to molded case circuit breakers, … These circuit
breakers are specifically intended to provide service entrance, feeder and branch
circuit protection in accordance with the National Electrical Code, NFPA 70.
UL 1077 – These requirements apply to supplementary protectors intended for use
as overcurrent; or, over- or under-voltage protection within an appliance or other
electrical equipment where branch circuit protection is already provided, or not
required by the standard.
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UL Safety Standard Differences
Standards
UL 1077: Supplementary Protector
UL 489: Circuit Breaker
● UL Recognized – Carries specific conditions for use
(acceptability) that must be followed to ensure that the
device will meet minimum electrical and shock
requirements.
● UL Listed – Carries no conditions of use (acceptability)
● Provides equipment (load) protection
where branch circuit protection is already
provided.
● Provides branch circuit protection in
accordance with the National Electrical
Code. (conductor/wiring system short
circuit protection)
● Cannot be applied as a motor branch or
branch circuit protection device.
● Allowed to be tested with a branch
circuit device in series with the
supplementary protector.
● Typically not required to close on fault
conditions.
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● Motor branch circuits can be protected
by a UL 489 device.
● Not allowed to rely on a series
protective device for conductor
protection.
● Required to close on fault conditions
November, 2006
OEM Control Components
UL Safety Standard Differences
Standards
UL 1077: Supplementary Protector
UL 489: Circuit Breaker
● Has a typical short circuit current rating
of 5,000 A, but need not have been
evaluated for short circuit conditions
during the recognition. May be evaluated
for greater than 5,000 A and may be
evaluated at any value declared by the
manufacturer.
● Has minimum short circuit interrupting
ratings of 5,000 A at 250 V or less; and,
10,000 A at above 250 V.
● Has no standard trip curve established
by the product safety standard to ensure
protection of conductors in the event of
an overload or short circuit condition.
●Has trip-curve characteristics developed
for protection of branch and feeder circuits.
● Overload protection – 1-1/2 times rating
Horsepower rating: 6 times rating.
● Spacing (UL 100, 600V, General
Industrial Use): 3/8 inch through air and
½ inch over surface.
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● Overload protection – 6 times rating.
● Spacing (UL 489, 600 V): 1 inch through
air and 2 inches over surface.
November, 2006
OEM Control Components
Supplementary Protector Check List
Does the supplemental protector meet or exceed the application conditions?
Check List
BE SURE that the supplemental protector has a short circuit current rating equal to or greater than the
available short circuit current of the installation.
CHECK THE VOLTAGE RATING against the system voltage. If the supplemental protector has a slash
voltage rating, i.e. 480Y/277, be sure it will be properly applied. For instance, a rating of 480Y/277 volts can
not be used on a 480 volt high resistance grounded wye system, 480 volt corner grounded delta system, or a
480 volt ungrounded system. It can only be applied on a 480/277 volt solidly grounded wye system.
The supplementary protector is not intended to a used as a disconnect.
Check to insure the specific time current characteristics of the supplemental protector provides the
intended protection for equipment under ALL CONDITIONS.
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Supplementary Protector Check List
Check to insure that the supplemental protector is NOT BEING MISAPPLIED as BRANCH CIRCUIT
PROTECTION
Check List
Check to insure the proper branch circuit protective device is ahead of the supplementary protector. Most
supplemental protectors are evaluated under short circuit conditions with a branch circuit fuse or circuit
breaker ahead of them.
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Advantages of Supplementary Protectors
 Small Installed Size
Advantages
 Precise Component Protection – protects components better than conventional
circuit breakers during short circuits
 Resetable After A Fault (if not a fuse)
 Tripping Selectivity
 Fault Isolation – only part of the circuit is affected
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Typical Supplementary Protector Applications
Applications
Automotive Systems
• Appliances
Control Circuits
 Control Instrumentation
 Enclosed Panel Heaters
 Lighting Circuits
 Medical Equipment
 PLC I/O
 Power Supplies
 Receptacles in Enclosed Panels
 Relay/Contact Coils
 Solenoids
• Test Equipment
• Transformer Primary & Secondary
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
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