Low Voltage Circuit Breakers

Presented by: Pete Rossomando – Director of PCS Applications Engineering

Confidential Property of Schneider Electric | Page 1

Confidential Property of Schneider Electric
Low Voltage Circuit Breakers
■ What are all these things????

Molded Case
Insulated Case

Thermal Magnetic Power Breaker

Metal Frame
UL489
Fixed Solid State
UL1066
Standard
ANSI Rated
Fused
80% Rated
100% Rated

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Low Voltage Circuit Breakers

■ Types of Circuit Breakers

■ Molded Case Circuit Breakers
■ Low Voltage Power Circuit Breakers

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Types of Circuit Breakers – What is a circuit breaker

■ A circuit breaker’s function is to “break” a circuit if there’s an overload or a short circuit

■ A circuit breaker’s purpose is to protect a circuit, equipment and conductors from
damage personnel in the event of an overload or short circuit
■ Circuit breakers can be used in control sequences in Power Control Systems
■ The American National Standards Institute (ANSI) defines a circuit breaker as “A
mechanical switching device, capable of making, carrying and breaking currents under
normal circuit conditions. Also capable of making and carrying for a specified time and
breaking currents under specified abnormal circuit conditions, such as those of a short
circuit.”
■ The NEC defines a circuit breaker as “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 it’s rating.”

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Types of Circuit Breakers

■ There are many different types of Circuit Breakers

■ With lots of different names
■ Molded Case
■ Insulated Case
■ Metal or Air Frame
■ Universal
■ And lots of others
■ The name refers to how the breaker is made
■ Names don’t describe the UL standard a circuit breaker meets, it’s interrupting rating or
it’s quality

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Low Voltage Circuit Breakers
■ Types of Circuit Breakers
■ Molded Case Circuit Breakers
■ Low Voltage Power Circuit Breakers

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Molded Case Circuit Breakers
■ What’s a molded case circuit breaker?
A molded case circuit breaker is defined as a circuit breaker that is assembled as an
integral unit in a supportive and enclosed housing of insulating material – Basically
a molded plastic case.
There are two types of molded case circuit breakers, thermal magnetic and solid
state

Internal Electromechanical Trip Unit

Solid State Trip Unit

Handle Rating

Solid State Thermal Magnetic

Molded Case breakers are listed to UL 489

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Molded Case Circuit Breakers
■ Thermal Magnetic Circuit Breakers - Circuit breakers that interrupt current when the
current becomes too high by operating a trigger device (electromechanical trip unit)
in the breaker. The contacts conducting the current are separated by preloaded
springs. The circuit breaker registers the current either by the current's heating
effect or by the magnetism it creates in passing through a small coil.

Internal
Electromechanical
Trip Unit

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Thermal Magnetic Circuit Breakers

■ Thermal Trip - used for overload protection

■ A bimetal strip made of two dissimilar metals bonded together.
The two metals have different thermal expansion characteristics,
so the bimetallic strip bends when heated.
■ When current flows through the strip, heat causes it to bend.
The more current, the hotter it gets and the more it bends. When
the strip bends a predetermined distance it makes contact with
the trip bar and activates the trip mechanism opening the
breaker
■ When the circuit breaker opens, the strip cools off and returns to
its original position. The breaker can be manually reset once the
overload condition has been corrected.

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Thermal Magnetic Circuit Breakers

■ Magnetic Trip – used for short circuit protection

■ Current flows through the breaker’s contacts creating opposing magnetic
fields. When a short circuit occurs the forces increase significantly.
■ The current that flows through the contacts also flows through a
conductor that passes close to the circuit breaker’s trip mechanism. At
fault current levels, the magnetic field surrounding the conductor
provides sufficient force to unlatch the trip unit and trip the breaker.

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Molded Case Circuit Breakers – 80% vs. 100% rated
■ What does an 80% breaker mean?
■ An 80% rated breaker as defined by the NEC requires the application load not to exceed
80% of the handle rating. Breakers are sized at 125% of continuous loads and non
continuous loads. Sometimes called a “standard breaker”
■ An 80% rated breaker can only be applied continuously (defined as 3 hours or more by the
NEC) at 80% of it’s continuous current rating. 100% rated circuit breakers can be applied
at up to 100% of their continuous rating continuously. Breakers rated at 80% can be
applied at 100% of their rating if the loading will last for less than 3 hours.
■ There are different testing requirements in UL489 for 80% and 100% rated circuit breakers
■ Translation #1 – A 1000 Amp 80% rated breaker can carry 1000 amps for 3 hours per NEC.
It can carry 800 amps forever.
■ Translation # 2 – A 1000 Amp 100% rated breaker can carry 1000 amps forever

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Molded Case Circuit Breakers – 80% vs. 100% rated
■ It’s not just the NEC – From the UL white book
■ “Unless otherwise marked, circuit breakers should not be loaded
to exceed 80% of their current rating, where in normal operation
the load will continue for 3 hours or more”

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Molded Case Circuit Breakers – 80% vs. 100% rated

Is this an 80% rated

breaker or a 100% rated
breaker?
You can’t tell by looking at
the breaker. Some are
identified on the label
some have to be checked
by Part#

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Molded Case Circuit Breakers – 80% vs. 100% rated
■ FAQ: Will an 80% rated circuit breaker trip if 80% of its rating is exceeded??
■ Answer – No, the 80% rating is an NEC restriction designed to prevent over-heating and
nuisance tripping of enclosed breakers and breakers in panelboards and switchboards
■ FAQ: Does a service entrance rated breaker have to be rated 100%
■ Answer – No, service entrance rated breakers can be rated 80%
■ FAQ: Is a 100% rated circuit breaker better than an 80% rated breakers
■ Answer – If applied properly and per code each will perform as required

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Low Voltage Circuit Breakers

■ Types of Circuit Breakers

■ Molded Case Circuit Breakers
■ Low Voltage Power Circuit Breakers

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Low Voltage Power Circuit Breakers
■ Aren’t they all “Power Circuit Breakers”?
■ It can be confusing. “Power Circuit Breaker” is an industry term, like “Utility Grade”. It
implies something and is referred to in some standards (Ul1066).
■ There are many standards they must meet.
■ Power Circuit Breakers are referred to by lots of different names:
■ Metal Frame
■ Insulated Case
■ Air breakers
■ ANSI Rated
■ Dual Rated or Universal

■ And lots of different standards:

■ UL1066
■ UL489
■ ANSI 37.50, 37.13, 37.16, 37.17
■ NEMA SG-3

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What’s the difference between an ANSI/Power/Metal frame breaker and an
Insulated Case breaker?
■ An ANSI/Metal Frame breaker describes a circuit breaker that was traditionally built as
an assembly of parts on a welded metal frame. It is tested to UL standard 1066 which
requires compliance with ANSI standards C37.13,C37.16,C37.17 & C37.50. ANSI requires
breakers to be drawout. Ex: SqD MTZ, Eaton Magnum DS, GE Wavepro, Siemens WL
■ An insulated case breaker is similar to a molded case breaker, built on a frame inside an
“insulated” molded plastic case. They are tested to the same UL489 standard as
molded case circuit breakers Ex: Eaton Magnum SB or SPB, GE Powerbreak, SqD SE,
Siemens SB
■ At one time all breaker manufacturers had separate products lines for insulated case
UL489 listed breakers and ANSI/metal frame UL1066 listed circuit breakers
■ The main difference is how they are tested. UL1066 tests for both interrupting rating
and short time rating. UL 489 does not require the same short time test.
■ Over time the lines have blurred between the breaker types. Most manufacturer’s offer
“dual rated” breakers. It’s not the name, it’s how the breaker is tested. Ex: SqD NW or
MTZ, Eaton Magnum DS, Siemens WL, GE Entelligard, ABB Emax2
■ Think UL1066 vs. UL 489
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UL Standards - UL489 & UL1066

UL 489 - Molded-Case Circuit Breakers, Molded-Case

Switches and Circuit-Breaker Enclosures UL 1066 – Standard for Safety for Low-
Voltage AC and DC Power Circuit Breaker
used in Enclosures

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UL Standards - UL489 & UL1066

UL 489
UL 1066

■ No ANSI Standard requirements ■ Complies with ANSI Standards

■ Drawout Not Required ■ Requires Drawout Breakers
■ No short time testing ■ Requires short time testing
■ Breakers rated at 80% or 100% ■ Breakers always rated at 100%
■ 500 cycle endurance test ■ 800 cycle endurance test
■ Sealed case, fixed mount, no replaceable parts can prevent normal ■ Allows for maintenance of internal components - drawout
maintenance
■ Required in UL1558 Switchgear can be used in UL891
■ Used in UL891 Switchboards can not be used in UL1558 Switchgear Switchboards
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 Low Voltage Power Circuit Breakers
■ What’s a power circuit breaker?
Arc Chute and
■ Main Components chamber
■ Disconnects/Stabs
■ Main Disconnects –
Connects breaker to main
bus
Main Disconnects/Stabs
■ Secondary Disconnects –
Connects Control Circuits to
the circuit Breaker Main Contacts
■ Arc Chutes – Interrupt and
contain an arc
■ Main Contacts – Carries the load
current
Secondary
■ Operating Mechanism – Opens Disconnects
and Closes the circuit breaker –
Spring mechanism
■ Overcurrent Trip Device – Solid
State/Digital Trip unit

Operating Mechanism
Trip Unit

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Low Voltage Power Circuit Breakers – Operating Mechanism
■ Operating Mechanism – Opens and Closes the circuit breaker – Spring mechanism
■ Springs provide the force to open and close the circuit breaker
■ A “Charged” spring means the springs are compressed and are ready to open or close the breaker
■ Spring charging accomplished via a manual charging handle on the front of the breaker or automatically via a
charging motor
■ The spring-charging motor automatically charges the spring mechanism for closing the circuit breaker and
also recharges the spring mechanism when the circuit breaker is in the ON position. Allow for reclosing of the
breaker after it’s been opened.

Manual Charging Handle Internal Springs

Rotating Shaft
Operating Mechanism

Confidential Property of Schneider Electric | Page 21

Current Power Circuit Breaker Offerings

Square D NW Square D MTZ Siemens WL & WLF

Eaton Magnum DS ABB Emax2

GE Entelliguard
Power Circuit breakers are listed to UL 489 or UL1066
Confidential Property of Schneider Electric | Page 22
What’s a Dual Rated or Universal Breaker?
A Dual Rated Breaker is a Breaker that meets both UL489 and UL 1066 Standards

A Universal Breaker meets both UL standards and IEC standards

Siemens WL
Square D NW Square D MTZ Eaton Magnum
DS

ABB Emax2 GE Entelliguard

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And Just when you thought you had it figured out……
All of these manufacturers………

Eaton Magnum DS
Siemens WL
Square D Square D MTZ
NW

GE Entelligard
….Have UL489 and UL1066 versions of their breakers

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Drawout Power Circuit Breaker – “Element”

Element – Current Carrying component

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Drawout Power Circuit Breaker – “Cell”

■ Cell
■ Cradle
■ Substructure
■ Cassette
■ Mounted in Switchgear or
Enclosure
■ Houses the Breaker Element

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Power Circuit Breaker Features/Options
■ All “Low Voltage Power Circuit breakers” are provided with Integral Solid State Trip Units
that may have “Long, Short, Instantaneous and Ground Fault” trip settings

Eaton Digitrip GE Entelliguard

Siemens ETU Trip Unit Trip Unit
Square D Micrologic Square D Micrologic Trip Unit
Trip Unit X Trip Unit
Main purpose is to open the circuit breaker in an overload or short circuit event
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Solid State Trip Units
Trip Indication
■ Allows operator to program various
settings via dials or screen
■ Allows operator to adjust trip settings
■ Can be provided with lots of display
information, electrical
parameters/metering, harmonics, trip
data, event data
■ Can be provided with communications
options
■ Provides Trip Indication
■ QR Code with breaker information Trip Unit Display
■ Bluetooth Connectivity

Adjustable Settings

Confidential Property of Schneider Electric | Page 28

Solid State Trip Units - LSIG
■ What do all these things mean?
■ Long Time – Protection against overloads and short circuits.
Causes the breaker to wait for inrush currents to subside
without tripping. Long time delay is the length of time the
breaker will hold an overload (running overcurrent) before
tripping. Sets the trip rating
■ Short Time – Protection against short circuits. Determines the
amount of current the breaker will carry for a short time
period, allowing down stream circuit protective devices to
open and clear the fault without tripping the up stream
breaker.
■ Instantaneous – Protection against short circuits. Trips the
circuit breaker with no intentional delay at any current
typically between 2 and 40 times the breaker’s continuous
ampere setting.
■ Ground Fault – Protection against ground faults. Trips the
breaker at a preset percentage of ground fault current.

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Trip Unit Accessories – Arc Flash Protection
■ Many circuit breakers can be provided with arc flash protection –
Referred to as ERMS or ARMS
■ Engaged when equipment requires maintenance within the Limited
Approach Boundary but can not be de-energized ERMS Blue LED
■ Does not eliminate arc fault incidents
■ Decreases the hazard associated with an arc fault by decreasing the ERMS Blue Display Backlight
time the fault is allowed to exist
■ Energy Reduction Maintenance Switch (ERMS) – Used for Arc Flash
Protection.
■ When activated the trip curve settings are changed to a dedicated
ERMS trip curve with adjustable L,S,I or G
■ Some versions are based on a lower Instantaneous setting when
activated
■ Trip time can be reduced to as low as 30ms
■ Can be activated from a dedicated, lockable switch or via Bluetooth
with smart phone App
■ Complies with NFPA 70E

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Solid State Trip Units – Zone Selective Interlocking
■ Interconnects circuit breaker trip units.
■ Short Time and Ground Fault functions can be interlocked
■ Downstream trip units tell upstream units a fault has occurred
■ Upstream trip unit doesn’t trip during the fault condition.
■ Downstream unit immediately tells its breaker to trip
■ Requires proper coordination of breakers/trip units to work properly

Upstream trip unit

Downstream trip unit

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Power Circuit Breaker Features/Options
■ Integral Solid State Trip Units – Trips the circuit breaker
■ UL489 versions available in stationary or drawout configurations
■ Interrupting capacity up to 200KAIC
■ Electrically or Manually operated
■ Shunt trip – Allows for remote electrical tripping of the breaker
■ Bell alarm or Overcurrent Trip Switch(OTS) – Provides a contact to signal the breaker
has been tripped
■ 2 “a” & 2 “b” aux contacts – “a” is open when the breaker is open and “b” is closed
when the breaker is open. All breakers in PCS systems are provided with 4a & 4b
contacts
■ Rating Plug – Sets the breaker trip rating
■ Truck Operated Cell Switch (TOC) – Provides a contact to indicate the breaker is drawn
out
■ Undervoltage Release (UVR) – Trips the breaker upon a preset undervoltage setting
■ Shutters
■ Communications, metering, protective functions
■ Hand Held & Full Function Test Kits
■ Remote Racking Device
■ Arc Flash Protection

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Power Circuit Breaker – Electrically vs. Manually operated
■ Manually operated is exactly as it states. The circuit breaker is opened, closed and
charged manually from pushbuttons and a charging handle on the front of the
breaker.

Charging Handle

Breaker Open
Pushbutton Breaker Close
Pushbutton

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Power Circuit Breaker – Electrically vs. Manually operated
■ Electrically operated adds some accessories to operate the breaker “remotely”.

Spring Charging
Electronic Shunt Trip
Motor

Electrically charges springs. Electrically opens Circuit

Receives close signal Breaker
Typically operates on
Typically operates on 24VDC from external
120VAC provided by via a source – Other AC or
CPT – Other AC or DC DC voltages available
voltages available

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Circuit Breaker Accessories

Open/Close Pushbutton Covers - A

transparent cover blocks access to the
push buttons used to open and close the Shutters automatically block access
the circuit breaker. Cover is lockable to the main disconnects when the
circuit breaker is in the disconnected,
test, or fully withdrawn position.

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Circuit Breaker Accessories

Remote Racking Device -Allows the

operator to perform circuit breaker 1. Drive Unit
racking from a distance of up to 30 2. Control Unit
feet. Distance exceeds the arc flash 3. Control Cable – 30 feet
boundary described in the arc flash 4. Power Cable
safety guidelines in NFPA-70E.

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Circuit Breaker Accessories

Full Function CB Test Kit –

Verifies LSIG functionality, Hand Held CB Test Kit –
Trip Unit Operation, Verifies Circuit Breaker
Mechanical Operation Trip Unit Operation

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Frame Size, Rating Plug, Trip Rating

■ Frame Size – Maximum continuous current carrying capability a

specific circuit breaker is capable of. Breaker can be damaged if the
current exceeds the frame size

■ Rating Plug – Sets the maximum ampere trip level the breaker senses.

■ Trip rating – The Ampere rating a breaker is set to trip at

■ Ex: A 2000 Amp Frame circuit breaker can be provided with a 1600 Amp
rating plug
that is set to trip the breaker at 1000 Amps

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Low Voltage Power Circuit Breakers - Ratings
Frame AIC Ratings @ 480
Manufacturer Type Fusible
Sizes Volts
800A –
Square D NW/MTZ – ANSI/UL 1066 Up to 200K Not Available
6000A

Square D NW/MTZ – UL489 Version 800A-6000A Up to 150K Not Available

800A – Up to 150K - 200K

Siemens WL – ANSI/UL 1066 Yes
5000A w/fuse
800A –
Siemens WL – UL 489 Up to 150K Not Available
5000A
800A –
Eaton Magnum DS – ANSI/UL1066 Up to 200K Not Available
6000A
Eaton Magnum SB - UL489 800A-6000A Up to 200K Not Available
800A –
Eaton Magnum DSL - UL1066 200K w/fuse Yes
2000A
800A –
GE Entelliguard ANSI/UL1066 Up to 150K Not Available
5000A
800A –
GE Entelliguard - UL489 Up to 150K Not Available
6000A
Up to 85K 200K
GE Wavepro – ANSI/UL1066 800A-5000A w/fuse Yes

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Low Voltage Circuit Breakers – Typical Applications

Paralleling Distribution Utility Circuit UL891 UL1558

Type Circuit Breaker Circuit Breaker
Panelboard
Breaker Switchboard Switchgear

Molded Case No Yes Yes No Yes No

Insulated
Yes Yes No Yes Yes No
Case/UL 489

ANIS/UL 1066 Yes Yes No Yes Yes Yes

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Power Circuit Breakers - FAQ’s

■ FAQ: Can all Power Circuit Breakers achieve 200KAIC@ 480V?

■ Answer – No, fused versions and some unfused versions can achieve 200KAIC.
■ FAQ: Can all Power Circuit Breakers be used in UL1558 switchgear?
■ Answer – No, Only UL 1066 listed breakers can be used in UL 1558 applications.
■ FAQ: Is Interrupting Rating the same as ATS Withstand Current Rating?
■ Answer – No, Interrupting rating defines the maximum short circuit current a circuit
breaker can interrupt. Withstand Current Rating defines the ability of a transfer
switch to withstand the thermal and electromagnetic effects of short circuit currents
for a set period of time.

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