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UL 508 A standard-compliant design
of industrial control panel
Axel Jöhnke
System Architecture Expert
14-15 SEPTEMBER 2011, MUNICH
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Agenda
● Origin and Comprehension
● Organizations
● Certificates
● NEC versus UL
● From NEC to SCCR
● Exercise
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Origin of UL
● 1893 Chicago World Exhibition
● Fire caused by electrical
failure
● 1894 „Underwriters Electrical
Bureau“ founded by William H.
Merrill
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Hazards covered?
Fire
Electrical Hazards
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Mechanical Hazards
4
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Jurisdiction
Federal Government
Basic requirements
State Governments
+ Additions
Local Governments
+
Additions
All industrial installations are affected!
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The North American Electrical Safety System
Installation
Codes
NEC,
CEC,
MEC
Product Standards
and Certification
Inspection and
Enforcement
UL, CSA, ANCE
IAEI, OSHA
Safe
SafeProducts
Productsand
and
Safe
SafeInstallations
Installations
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Panel SCCR is US Regulatory Requirement
National Fire Protection Association
● NFPA 70 (NEC, National Electrical Code)
● 2005 NEC Article 409 “Industrial Control
Panels”
● Short Circuit Current Rating Marking
National Electrical Code
● Safety Standards
Underwriters Laboratory
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● UL508A
● Standard for Industrial Control Panels
● NFPA 79
● Electrical Standard for industrial
Machinery
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NEC adoption by State
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Inspection and Enforcement
● Authorities Having Jurisdiction (AHJ’s):
● “the organization, office, or individual responsible for approving
equipment, materials, an installation, or a procedure.”
● International Association of Electrical Inspectors
● electrical inspectors
●
●
●
●
●
●
testing agencies
standards organizations
manufacturers
distributors
installers
contractors
● Occupational Safety and Health Administration
● sets and enforces protective workplace safety
and health standards
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UL Marks (extraction)
End Products
Complete Components
Factory and
Field Installation
Specific Properties,
Limited Range of Hazards
Under limited or
Special Conditions
Compliance with UL's Listing and
Follow-Up Service
Canada
United States
Component Parts
Part of a larger Product or System
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2005 NEC – Article 409
● Why new Article 409?
● Previously, only limited guidance to ensure electrical safety for the
numerous control panels not listed
● Minimum requirements for the safe installation and inspection of industrial
control panels
• Air Conditioning and Refrigeration - Article 440
• Crane & Hoist Control – Article 610
• Elevator Control – Article 620
• Industrial Machinery – Article 670
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Article 409 Requirements Covers:
● Article 409 – Industrial Control Panels
● Conductor Sizing
● Overcurrent Protection
● Location and Rating
● Disconnecting Means
● Grounding
● Enclosures
● Busbar arrangement
● Wiring Space
● Service Entrance Requirements
● Markings
● Short Circuit Current Rating
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SCCR = Short Circuit Corrent Rating
● In the US industrial
control panels must be
marked with a SCCR
(Short Circuit Corrent
Rating). The NEC 2011
Article 409 describes
the terms of the short
circuit resistance
marker on the panel.
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Short Circuit Current Rating (SCCR)
Terminology
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● Circuit Breakers and Fuses are marked with an AIC (Ampere Interrupt
Current) or interrupting short circuit rating. They are considered “active”
devices and intended to interrupt a fault current.
● Motor control products (contactors, overloads, drives, etc.) are marked
with a current withstand short circuit rating. They are considered
“passive” devices and are not intended to interrupt a fault current.
● UL508A does not differentiate between an interrupt rating or withstand
rating and considers both to be the SCCR rating for the component.
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SCCR of the control panel?
Decisive factors of a cabinet for the SCCR:
● Local installation
●Available short
circuit fault current of the supply
●Effects of the power transformers impedances and the feed block
in front of the cabinet
● Cabinet specification – prescribing
●Authorities
Having Jurisdiction (AHJ), government,
judiciary,
●provider,
● machine- and controlbuilder
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What is the available fault current at the control panel?
2000kVA Distribution
Transformer
w/480V secondary
(2400 Amps)
36kA Available
30kA Available
300 Feet w/
(7) 750 MCM/phase
MCC Unit
480V, 2000 Amps
65kA rated
200 Feet w/
(2) 250 MCM/phase
23kA
Available
18kA
Available
100 Feet w/
1/0 AWG/phase
I-Line Panel Board
480V, 400 Amps
42kA rated
Step Down
Transformer
480/240V,
100kVA
100 Feet w/
(2) 250 MCM/phase
100 Feet w/
1 AWG /phase
I-Line Panel Board
480V, 400 Amps
42kA rated
11kA
Available
Control Panel
480V, 100 Amp
SCCR = 22kA
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4.3kA
Available
Secondary
Control Panel
240V, 200 Amp
SCCR = 5kA
10.5kA
Available
Primary
150 Feet w/
250 MCM/phase
3.4kA
Available
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SCCR marking
●Unmarked component rating
determined by Table SB4.1
●NOTE: Requires branch
circuit protection (Fuse or
Circuit Breaker) upstream
and sized per NEC, if
applicable
Minimum required
UL508 Low Fault Short
Circuit Withstand
Levels For Horsepower
rated devices
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Short Circuit Current Ratings
● How can panel manufacturers obtain the needed
SCCR for a given panel?
Three options:
1) Test each panel construction and record the
construction in their UL procedure (not cost effective,
destructive testing required)
2) Purchase previously tested constructions from a major
supplier of equipment, such as Schneider
Electric/Square D, that can be tabulated in the control
panel manufacturer’s UL procedure
3) Apply the method described in UL 508A, Supplement SB
(weakest-link)
Using interrupt rating of the main overcurrent protective
device for the panel is not an accepted method
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UL508A Example of Control vs. Power circuit
Terminology
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● UL508A Definitions
● 2.11 Control Circuit –
A circuit that carries the
electric signals directing
the performance of a
controller, and which does
not carry the main power
circuit. A control circuit is,
in most cases, limited to 15
amperes.
● 2.38 Power Circuit Conductors and
components of branch and
feeder circuits.
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UL508A Example of Feeder vs. Branch circuit
Terminology
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Feeder Circuit versus
Branch Circuit
● UL508A Definition
● Feeder Circuit Conductors and circuitry on
the supply side of the
branch circuit overcurrent
protective device.
● Branch Circuit Conductors and
components following the
last overcurrent protective
device protecting a load.
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UL 508A - Supplement SB4.3
(Optional Provision)
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● SB4.3 – Feeder components that
limit the short circuit current available
● SB4.3.1 – For branch circuits supplied by a
power transformer with an isolated secondary,
if:
a) The power transformer is rated not more
than 10kVA and all components in the
secondary circuit are rated at least 5kA; or
b) If transformer is rated not more than 5kVA,
with a maximum 120V secondary voltage, and
all secondary components are rated at least
2kA
● Then the SCCR of the primary overcurrent
protective device may be assigned to the line
side of the power transformer circuit.
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What is a UL Combination Motor
Controller?
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Type E
Product
Example
UL Combination Motor
Controller Classification:
Type D
Product
Example
Disconnect
Switch
Type A = Fuse
Type C = Thermal-magnetic breaker
Type D = Instantaneous trip breaker
SCPD
Type E = Self Protected
or
Type F= Manual Motor Controller
Controller
Overload
Load Break
Switch
Motor
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Branch Circuit with a rating of 65kA
Untested Combination Motor
Circuit SCCR = 5kA
(weakest-link)
Circuit Breaker SCCR = 65kA
Tested UL508A Combination Motor Controller
Option No. 3 of SB4.2
Tested Combination Motor Circuit
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
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Sample of UL validated Schneider Electric UL508A
Combination Motor Controller Data
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Data is submitted to UL for validation and then posted onto UL’s website. Information shown is from Square D’ UL508A micro-site.
1. UL ID number is the documentation for the combination.
Data is on Square D 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. Maximum rating for combination.
1
2
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3
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Sample of UL validated Schneider Electric UL508A
Combination Motor Controller Data
5. Minimum required enclosure volume for combination.
6. Conditions of use for combination.
7. Schneider Electric UL File where construction is described and previously
tested.
5
1
6
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TEST
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What is Panel SCCR?
480 Vac (delta)
FAL Circuit
Breaker
100A, 18kA
Self Protected
FAL
Breaker
18kA
Class J
U-Line
Fuses
130kA
100kA
Drive marked 22kA
when protected with
Class J fuses
5kA
Starter
Drive
Type E
with required
current limiter
& line spacer
is rated:
130kA, 480V
Also rated 65kA
at 600V
&
w/o current limiter
rated 480Y/277
V, 42kA
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Panel SCCR = 5kA
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480 Vac (delta)
FAL Circuit
Breaker
PANEL SCCR = 5kA
100A, 18kA
FAL
Breaker
Branch circuit
SCCR = 5kA
(weakest-link)
18kA
Class J
Fuses
100kA
Self Protected
U-Line
Type E
130kA
with required
current limiter
& line spacer
Drive marked 22kA
when protected with
Class J fuses
5kA
Starter
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Drive
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What is Panel SCCR?
480 Vac (delta)
Found UL508A
Combination Motor
Controller with
same starter but
with FHL breaker
(25kA) vs. FAL
breaker (18kA)
100A, 18kA
FHL
Breaker
100kA Tested
UL508A Combination
Motor Controller
UL ID No. SE303440
FAL Circuit
Breaker
25kA
Class J
Fuses
100kA
Self Protected
U-Line
130kA
Type E
with required
current limiter
& line spacer
Drive marked 22kA
when protected with
Class J fuses
5kA
Starter
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Drive
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Panel SCCR = 18kA.
480 Vac (delta)
FAL Circuit
Breaker
PANEL SCCR = 18kA
100A, 18kA
FHL
Breaker
100kA Tested
UL508A Combination
Motor Controller
UL ID No. SE303440
25kA
Class J
Fuses
100kA
Lowest rated power
component = 18kA
(weakest-link)
U-Line
Self Protected
130kA
Type E
Drive marked 22kA
when protected with
Class J fuses
with required
current limiter
& line spacer
5kA
Starter
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Drive
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What is Panel SCCR?
Current
Limiting
FIL Breaker
Could replace 18kA main breaker with
a 65kA breaker but would still have
only a panel SCCR = 22kA due to 22kA
drive circuit.
100A, 65kA
Option is to use Feeder Current
Limiting provision of SB4.3.
480 Vac (delta)
21 kA Let-through per breaker curve
FHL
Breaker
100kA Tested
UL508A Combination
Motor Controller
UL ID No. SE303440
25kA
Self Protected
Class J
Fuses
U-Line
Type E
130kA
with required
current limiter
& line spacer
100kA
Drive marked 22kA
when protected with
Class J fuses
5kA
Starter
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Drive
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Square D FIL36100 Breaker Let-Through Curve
From published letthrough curve for FIL
current limiting circuit
breaker, Ip = 21 kA at 480V
with 65kA available to FIL
circuit breaker
21 kA
65 kA
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Questions?
http://www.schneider-electric.us/sites/us/en/support/product-supportresources/ul-508a-support/ul-508a-support.page
www.infoPLC.net
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