1. UL/ANSI/NEMA
Low Voltage
Circuit Breakers

2. “System” Consideration
Product
Standards and
Certification
Installation
Codes
Safe Products and Safe
Installations
Inspection and
Enforcement
(verification)

3. UL Standards for LV components
UL 489: Molded Case Circuit Breakers
UL 1066: LV Power Circuit Breakers
UL 98: Enclosed and Deadfront Switches
UL 508: Industrial Control Equipment

4. UL Standards for LV Assemblies
UL 67: Panelboards
UL 891: Switchboards
UL 1558: LV Switchgear
UL 845: Motor Control Centers
UL 857: Busway
UL 508A: Industrial Control Panels

5. IEC Standards for LV Components
IEC 60947: LV Switchgear and Controlgear
Part 1: General rules
Part 2: Circuit breakers
Part 3: Switches, disconnectors…
Part 4 series: Contactors and motor- starters
Part 5 series: Control circuit devices and switching elements
Part …

6. IEC Standards for LV Assemblies
IEC 61439: LV Switchgear and Controlgear Assemblies
Part 1: General rules
Part 2: Power Switchgear
Part 3: Distribution boards operated by ordinary persons
Part 4: Construction sites
Part 5: Distribution in public networks
Part 6: Busbar Trunking Systems (Busways)
Part 7: Marinas, camping sites, market squares, EV charging

7. National Electrical Code, NEC
NFPA 70, contains “installation” rules
Cable connections = AWG sizes
Wire bending spaces
Enclosure type designations
Grounding
Working spaces
Creepage/Clearance distances
Temperature rises
Mentions “Listed” products
References “product” Standards (Annex A)
The NEC is the basis for your large installed Petro industry

8. UL conformity assessment
UL Listing provides
Independent confirmation of original design
On-going factory inspections
Periodic follow-up testing
Market surveillance

9. Support the installed “system”
UL Components
UL Assemblies
IEC Components
IEC Assemblies
SAFE

10. UNSAFE Do not “intermix” UL Components IEC Components UL Assemblies
IEC Assemblies

11. System Considerations - Summary
Support your installed electrical infrastructure
Concerns extend beyond individual components
Need alignment with Installation requirements
Certification confirms initial & continued compliance
Do not intermix IEC and UL products, it will compromise safety!

12. Background/Evolution: LV Power Breakers
UL 1066, Low-Voltage AC and DC Power Circuit Breakers Used in Enclosures
Robust
Large commercial & industrial applications

13. Low Voltage Circuit Breaker Standards IEC & UL
Low Voltage Switchgear
and Controlgear-Part 2
Circuit Breakers
UL 1066
UL Standard for
Low Voltage AC and DC
Power Circuit Breakers
used in Enclosures
Air
(Power)
Circuit
Breakers
Moulded
Case
Circuit Breakers
UL 489
UL Standard for
Molded-Case Circuit Breakers
IEC 60898
Circuit-breakers for
overcurrent protection for
household and similar installations

14. Key differences Power Circuit Breakers have compared to Molded Case Circuit Breakers
Electronic Trip Only
Used Primarily in Draw-out Switchboards
Serviceable and Maintainable
Typically used upstream from Molded Case Circuit Breakers
Provide a Higher Level of Selective Coordination
Stored Energy Mechanism

15. Many Standards differences between IEC 60947-2 and UL 1066, including
Testing Approach
For example, Short Circuit Interrupting Capability
Performance Requirements
For example:
Temperature Rise
Overload
Follow Up Test Requirements
For example, periodic UL 1066 Follow Up Testing

16. Power Circuit Breakers: Short Circuit Capability
IEC
UL 1066
Significant clause is 4.4: Utilization Categories
Category B “Determine rated short time withstand current”
Annex H Single Pole Interrupting – Optional
Ics: Rated Breaking Capacity (Seq. II)
Icu: Rated Ultimate Capability (Seq. III)
References ANSI/NEMA C37.50 for:
Short-Time Current Duty Cycle
Carry fault current for two 0.5 second periods
Short-Circuit Current Duty Cycle
Single Pole Test at 87% of Interrupting Capacity (ANSI C37.50 Table 4)
Short Circuit Current Tests required in each Test Sequence (C Table 1)
ANSI/NEMA C37.50 contains the testing specifics and is the “test standard”
UL 1066 is the Certification standard which simply refers to ANSI C37.50 for tests
UL requires defined/vigorous short circuit verifications and single pole interruption.

17. Philosophy different for temperature tests
Power Circuit Breakers: Temperature
IEC UL
Maximum Allowable Temperature Rise
80°C Enclosure not required, sample previously tested in Seq. I and Seq. II
55˚C Tested in the Enclosure, tested on a new sample (C37.50 Table 1 Sequence V)
Maximum allowable Temperature Rise
At the Circuit Breaker Contacts
No value specified but no damage to adjacent parts (Table 7 Note a)
85°C
These are the MAXIMUM temperatures permitted under completely stabilized conditions
UL has lower allowable temperature rises
Philosophy different for temperature tests

18. Power Circuit Breakers: Overload Capability
IEC UL
Overload test requirements
Required for 630A and less, optional above 630A
( and Test Sequence I)
Required for ALL circuit breakers (ANSI C37.50 Table 1, Seq. 1)
Tests after Overload
Short Circuit Test not required and not part of test sequence
Short Circuit Test required
UL always requires overload, also
Requires short circuit test after overload

19. Power Circuit Breakers: Conformance Testing/Conformity Assessment
IEC UL
UL Third-Party Witness of Conformance Testing
UL Factory Surveillance
UL “procedures” document the construction/components for on-going compliance
UL periodic Follow-up Testing based on production volume or number of years (ANSI C37.50 Table 7)
Conformance to IEC Standard (CE Mark) typically justified solely by manufacturer’s self declaration
Third-party certification assures independent verification & ongoing conformance

20. Emerging technology: Addressing Arc Flash Hazards
Data is available to apply UL low voltage circuit breakers to limit arc flash energy

21. Traditional Circuit Protection
Circuit breakers were originally intended to protect the installed conductors:
Protect & prevent possible damage for operating beyond their capability.
Cut-off current below the cable damage curves.

22. Arc Flash Hazards

23. IEEE 1584, Guide for Performing Arc-Flash Hazard Calculations
Calculate Incident energy
Use fault current level and interruption time of the overcurrent device.
Circuit breaker calculation methods do not account for their current limiting aspects!
Published Papers referencing circuit breaker arc flash applications are:
“Molded-Case Circuit Breakers reduce Arc-Flash Hazard Impact” NEMA (available for free download from the NEMA Website)
“Understanding IEEE 1584 Arc-Flash Calculations”, K. J. Lippert, D. M. Colaberardino, and C. W. Kimblin, IEEE IAS Magazine, May/June 2005.
Applying Low Voltage Circuit Breakers to Limit Arc-Flash Energy”, G. Gregory and K. J. Lippert, IEEE PCIC, September 2006

24. Comparison of MCCB arc test results
Incident Energy
at Bolted Fault Current (kA)
Min
Mid
Max
250 A MCCB with Thermal -
Magnetic Trip Unit
Bolted fault current
Inc. Energy via IEEE
1584
Table E.1
Generic
(Cal/cm 2 )
1584 & Trip Curve
Measured
Incident Energy (
Cal/cm
3.7 kA
N/A 1
27.6
0.11
35 kA
1.7
0.9
0.15
100 kA
4.7
1.8
0.13
400 A MCCB with Thermal
Incide
nt Energy (Cal/cm
6 kA 72
0.12
0.7
0.2
1.4
0.20
600 A MCCB with Thermal
Incident Energy (Cal/cm
9 kA 46
1.22
2.3
1.1
0.78
5.7
0.36
800 A MCCB with Thermal Me
asured
12 kA
61.4
0.86
1.14
65 kA
3.9
2.8
1.05
1200 A MCCB with Electronic Trip Unit
20 kA
218
1.86
3.5
1.20
9.4
5.8
1.64
2500 A MCCB with Electronic Trip Unit
(Cal
/cm
110
3.96
7.7
5.4
3.48
11.5
6.5
2.12 1.
N/A represents “Not Applicable” because the parameters are outside the range of the
IEEE 1584 Table E.1 generic equation.
Test data from IEEE paper by 2 major US MCCB manufacturers tests

25. Conclusions from Molded Case Circuit Breaker arc flash testing
In the instantaneous region, tested incident energies are significantly lower than calculated values due to:
Actual arcing time
Current reduction by the circuit breaker (particularly for current limiting circuit breakers)

26. Zone Selective Interlocking (ZSI)
Many modern circuit breakers have electronic trip units which make them more “intelligent”
Electronic trips with ZSI allows breakers in the same zone to communicate with each other
ZSI bypasses the preset short delay time (and ground fault delay time when available) on the upstream circuit breaker closest to the fault, which then trips with no intentional delay
ZSI is one method of getting breakers to operate instantaneously.
It’s applicable to many breakers which have electronic trip.
Upstream & downstream breakers in the same “zone” communicate with each other
During a fault condition, with ZSI it bypasses the Short Delay Time of the upstream breaker. Trips with NO intentional delay.
Faster tripping = less arc flash energy and STILL MAINTAINS SELECTIVE COORDINATION so that only the device closest to the fault opens!

27. Zone Selective Interlocking (ZSI)
When a fault occurs at point X... X
Feeder 1
Circuit Breaker
Feeder 2
Feeder 3
Main 1
I sense trouble!
All is OK here, so I’m quiet.
All is OK here, so I’m quiet.
All is OK here, so I’m quiet.
Zone A
The following are a series of graphics illustrations to help explain the concept of ZSI.
First Fly-in: In this example the fault occurs at point X.
Second-5th Fly-ins: The communications between the downstream & upstream breakers
NOTE: The words are not the actual communication (as our electronics guys have corrected me). I suggested them to more easily understand the concept.
Circuit Breaker
Circuit Breaker

28. Zone Selective Interlocking (ZSI)
But with ZSI… since none of my downstream buddies are telling me that they sense trouble, I know not to wait at all, and open as quickly as I can!
Feeder 1
Circuit Breaker
Feeder 2
Feeder 3
Main 1
Without ZSI, I’d normally wait for my Short Delay time, and then open! X
Zone A
Without ZSI: This is the standard situation when Short Delay settings are used.
With ZSI: The Short Delay setting is bypassed. No INTENTIONAL delay!
Circuit Breaker
Circuit Breaker

29. Zone Selective Interlocking (ZSI)
However, when a fault occurs at point XX... XX
Feeder 1
Circuit Breaker
Feeder 2
Feeder 3
Main 1
I sense trouble!
I sense trouble too! Hey upstream buddy, hang in there, I’ve got it!
All is OK here, so I’m quiet.
All is OK here, so I’m quiet.
Zone A
Further example to understand the REAL advantage:
When the fault occurs at point XX (on the load side of downstream device).
Fly-ins (only 1 click required)
Again there is communication between the devices.
Next Fly-in: MAJOR ADVANTAGE is Coordination is Maintained, while assuring Quick tripping!
Coordination
Is Maintained!
Circuit Breaker
Circuit Breaker

30. ZSI Arc Flash Example X Without ZSI = 0.5 S: With ZSI = 0.08 S:
Main 1
Circuit Breaker
Short Delay=
0.5S X
35kA fault current
* Using IEEE 1584: 480V-35kA, MCC, 18” from Arc
Circuit Breaker
Circuit Breaker
Circuit Breaker
Short
Delay=
0.3S
Short
Delay=
0.3S
Short
Delay=
0.3S
Feeder 1
Feeder 2
Feeder 3
Here is an example of how ZSI of breakers reduces Arc Flash Energy.
Repeat the delay settings: Upstream = 0.5S, Downstream = 0.3 S.
Fly-In 1: Explain where the fault occurs.
This example is based upon using IEEE 1584 calculation of 480V, 35Ka, MCC, 18” from Arc
Fly-In 2: WITHOUT ZSI - .5S = 43.7Cal = No PPE, so find other alternatives
Fly-In 3: WITH ZSI – 0.08S = 7 Cal = 2 PPE, which is a simple FR Shirt, Pants & Cotton underwear.
TAKE AWAY: ZSI reduces arc flash energy associated with circuit breakers, while maintaining coordination.
Without ZSI = 0.5 S:
43.7* Cal/cm2
Greater than Cat. 4 PPE!
FIND ALTERNATIVES!
With ZSI = 0.08 S:
7.0* Cal/cm2
FR Shirt & Pants +
Cotton underwear
Cat. 2 PPE

31. Arc-reducing maintenance switching
Manually or Automatically enables an instantaneous pickup
Trip Times May Vary Between Manufacturers
Some may be same as Instantaneous
Some my be faster than Instantaneous
Reduces arc energy to downstream equipment/personnel
Limits energy available during maintenance
EXAMPLE:
Normal settings calculates to 10.7 cal (Cat. 3)
With Arcflash Reduction Maintenance Switch 2.2 cal (Cat. 1)

32. Arc flash mitigation system
When activated, this technology continuously monitors current and voltage to identify an arc flash.
When an arc flash occurs, the arc is automatically dealt with, without changes to the circuit breaker.
Sometimes referred to as “crowbar systems”

33. Summary of UL circuit breaker applications to reduce arc flash energy
Use Arc flash energy values published by the circuit breaker manufacturer
Zone Selective Interlocking
Arc Reduction Maintenance Switch
Arc Flash Mitigation Systems
Summary of CB applications to reduce arc flash.
USA developed technologies.
Adjust settings (want instantaneous operation)
Use ZSI to reduce time (& corresponding energy) while maintaining selective coordination
Use CL breakers: specifically marked, drastically reduces let-through energy

34. Emerging technology: PV Circuit Breakers
UL 489B, Outline of Investigation for Molded-Case Circuit Breakers …for Use with Photovoltaic (PV) Systems

35. UL 489B and IEC UL 489B: First published July, 2010
Several manufacturers have UL Listed products
IEC
No published requirements yet for PV breakers
CD circulated

36. UL 489B PV Circuit Breaker Requirements
1500 V dc capability
Rated/marked for 50 C
Vigorous dc current tests
Evaluated for reverse direction current