UL508A: Control Panel Short
Circuit Solutions
Son Dinh
Control Panel Application Specialist
Schneider Electric
OEM Initi@tive 2008
Agenda
1. Short Circuit Current Rating (SCCR) requirements
2. UL508A, Supplement SB
3. Impact On Panel Design
4. Schneider Electric’s Solutions
Schneider Electric
- Division - Name – Date
2
Short Circuit Rating Requirements:
Background
Purpose of National Electric Code (NEC) Article 409 –
Industrial Control Panels
● Previously no specific requirements for the inspection
of control panels
● Provides minimum requirements for panel
construction
● Requirements enhances worker and application
safety that previously did not exist
● Allows for a safer integrated installation by requiring
panels to be marked with a Short Circuit Current
Rating (SCCR)
● Requires all panels be marked with a SCCR rating
Schneider Electric
- Division - Name – Date
3
Short Circuit Rating Requirements:
Marking
● 409.110 Marking.
An industrial control panel shall be marked with the following information
that is plainly visible after installation:
1. Manufacturers name, trademark or other descriptive marking by which the
organization responsible for the product can be identified
2. Supply voltage, phase, frequency, and full-load current
3. Short-circuit current rating of the industrial control panel based on one of the
following:
a. short circuit current rating of a listed and labeled assembly
b. short circuit current rating established utilizing an approved method
FPN: UL508A-2001 Supplement SB is an example of an approved method
Exception to (3): Short-circuit current ratings are not required for industrial
control panels containing only control circuit components.
Schneider Electric
- Division - Name – Date
4
Short Circuit Rating Requirements:
Safety standards requirements
● Safety Standards Also Require Panels to Have a SCCR rating
UL508A
Standard for Industrial
Control Panels
Schneider Electric
- Division - Name – Date
UL1995
Standard for Air
Conditioning and
Refrigeration Equipment
NFPA 79
Electrical Standard for
Industrial Machinery
5
Short Circuit Rating Requirements:
What is appropriate SCCR for a panel?
Contributing Factors to Panel SCCR Rating:
● Installation Site
● Short circuit fault current available to panel or equipment.
● Power transformer and conductor impedances before supply terminals of control
panel/equipment all impact and help lower available fault current.
● Panel Specifications
● Facilities Engineer,
● Consulting & Design Engineer,
● Panel/Machine Builder
Schneider Electric
- Division - Name – Date
6
Short Circuit Rating Requirements:
Available fault current and appropriate SCCR rating
Schneider Electric
- Division - Name – Date
7
Short Circuit Rating Requirements:
Available SCC at transformer output terminals
Schneider Electric
- Division - Name – Date
(Takes a very large transformer to
allow for 65kA or higher fault current)
8
Short Circuit Rating Requirements:
How is panel SCCR determined
● Test each panel construction and have described in
follow-up procedure
● Costly and destructive testing required
● Third party testing and certification required
● Purchase previously tested combinations and
constructions
● Use an approved method
● like Supplement SB of UL508A (weakest-link).
● Compliance with UL508A = compliance with NEC 409.
Using interrupt rating of the main overcurrent protective
device for the panel is not an accepted method
Schneider Electric
- Division - Name – Date
9
Agenda
1. Short Circuit Current Rating (SCCR) requirements
2. UL508A, Supplement SB
3. Impact On Panel Design
4. Schneider Electric’s Solutions
Schneider Electric
- Division - Name – Date
10
UL508A, Supplement SB
Calculation method based on power component rating
● SCCR Rating Based on Weakest-Link
● Lowest SCCR Rated Power Component in
Panel
● Only applicable to power circuit, control circuit
not included in calculation
● Component SCCR rating determined by one
of the following
● Marked rating on component or on instructions
provided with the component
● Assumed short circuit rating from Table SB4.1
● Rating of a UL tested combination or UL508A
Combination Motor Controller
Schneider Electric
- Division - Name – Date
11
UL508A, Supplement SB
SCCR component marking
Product
Label:
Product
Carton:
Exceptions: Power transformers, reactors, current transformers, dry-type capacitors,
resistors, varistors, and voltmeters are not required to have a short circuit current rating.
Schneider Electric
- Division - Name – Date
12
UL508A, Supplement SB
Default SCCR values
● Table SB4.1 – Unmarked
Components Default SCCR Values
● Requires branch circuit protection
(Fuse or Circuit Breaker) upstream and
sized per NEC, if applicable. This is
not the stand alone SCCR rating for
device.
Schneider Electric
- Division - Name – Date
13
UL508A, Supplement SB
Tested Combination Motor Controller
Untested Combination Motor Circuit
SCCR = 5kA (weakest-link)
Tested Combination Motor Controller
Circuit, SCCR = 65kA
Circuit Breaker
SCCR = 65kA
UL508A Tested
Combination Motor
Controller = 65kA
Contactor
SCCR = 10kA
SCCR rating of
tested combination is
higher than SCCR
rating of individual
components that
make up the motor
combination
Overload relay
SCCR = 5kA
Schneider Electric
- Division - Name – Date
14
UL508A, Supplement SB
What is a UL Combination Motor Controller?
Type E
Example
Classification:
● Type A
Fuse
Disconnect
Switch
● Type C
Thermal-magnetic breaker
SCPD
● Type D
Instantaneous trip breaker
Type D
Example
or
Controller
● Type E
Self Protected
Overload
● Type F
Self Protected –Manual
Motor Controller
Load Break
Switch
Schneider Electric
- Division - Name – Date
Motor
15
Agenda
1. Short Circuit Current Rating (SCCR) requirements
2. UL508A, Supplement SB
3. Impact On Panel Design
4. Schneider Electric’s Solutions
Schneider Electric
- Division - Name – Date
16
Impact on Panel Design:
How UL508A impacts OEMs
● Component Selection Is Critical In Order To Achieve Desired SCCR Rating
● Specific SCCR rated components and tested combinations are a must
● Extremely difficult to obtain a high SCCR rating by intermixing components
from different manufacturers
● Panel Design Considerations
● One size fits all design will require Higher SCCR rated components and will
increase costs for everyone involved,
● High SCCR rated panels may require more enclosure volume,
● Component selection may be limited depending on desired SCCR rating,
● Determining panel SCCR rating will require more labor and supporting
documentation,
● 100kA rated panel may not be safer or protect equipment as well where only a 5 or
10kA fault current is available,
Schneider Electric
- Division - Name – Date
17
Impact on Panel Design:
How UL508A impacts OEMs
● Installation & Maintenance Considerations
● Is panel rated for available fault current of
installation site,
● May be asked by inspector or customer to
prove and provide calculation and supporting
documentation in the determination of SCCR
rating,
● Field modifications and upgrades,
● Replacement parts will need to be like for like,
Schneider Electric
- Division - Name – Date
18
Agenda
1. Short Circuit Current Rating (SCCR) requirements
2. UL508A, Supplement SB
3. Impact On Panel Design
4. Schneider Electric’s Solutions
Schneider Electric
- Division - Name – Date
19
Schneider Electric solutions
UL508A Knowledge
UL508A Web site
www.oem.schneider-electric.com
> Standards and legislation
● Interactive NEC Code Adoption Map
● Extensive FAQs & literature
● How to establish SCCR rating
Flowcharts
● Industry’s broadest offering of UL
validated and tested combination motor
controller data
Schneider Electric
- Division - Name – Date
20
Schneider Electric solutions
UL Tested Solutions
Contactors**:
D.P. = 100kA
w/fuses & 65kA w/
Square D
Breakers
Up to 100kA Combinations
42kA to 130kA
Up to 100kA
Combinations
Circuit
breakers 10 to
100kA
UL508A 65kA
Soft-Start
Combination
Up to 65kA
- GV (Type E)
motor circuit
protectors,
IEC – 100kA
w/fuses
** Pending product label/documentation update
Schneider Electric
- Division - Name – Date
Drives** SCCR:
Up to 100kA SqD breakers
Up to 100kA
- fuses
21
Schneider Electric solutions
Tested combination motor controller data benefits
● Lower cost through fewer components
● Tested and UL validated and certified
● Meet all your application needs
● Less documentation required to prove
SCCR rating
● Reduce labor costs & simplify panel
construction and calculation of panel SCCR
rating
Schneider Electric
- Division - Name – Date
22
Schneider Electric solutions
UL validated data available online
Schneider Electric
- Division - Name – Date
23
Schneider Electric solutions
UL508A Combination Motor Controller Data
1. UL ID number is the documentation for the combination. Data is on
Schneider Electric and UL’s UL508A website.
2. Required components for each combination are specified.
3. Combination SCCR rating (higher that any individual component forming the
combination).
4. Minimum required enclosure volume for combination specified.
5. Schneider Electric UL File where construction is described and previously
tested.
Schneider Electric
- Division - Name – Date
24
Conclusion
● Factors that determine panel SCCR rating?
● the available fault current to panel,
● panel specifications (end-user, consulting or design engineer),
● Panel SCCR rating will impact
● component selection
● panel design and cost
● Compliance Made Simple
● Schneider Electric offers a full range of power protection, automation, and control
products with SCCR ratings ranging from 10kA to 100kA
● Schneider’s extensive UL508A knowledge online
Schneider Electric
- Division - Name – Date
25
Schneider Electric
- Division - Name – Date
26