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Slide1
Suggestion on How to Use
Industry Trainers are encouraged to use this material in their sessions
Download the presentation file
Print the Notes pages and read them as you view the presentation in the “Slide Show” view. In this way you see the slides in large format and have animation (when available)Slide2
Types of Overcurrent Protective DevicesSlide3
Circuit Breakers
NEC
® Definition - Article 100
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.Slide4
Thermal-Mag CB Construction
Molded case
f
rame
provides insulated housing for components
Contacts
open and close circuit
Handle or Operating mechanism opens and closes contacts – cannot be “teased” - quick-make, quick break
Handle or
Operating
Mechanism
Contacts
Arc
Extinguishers
(Arc Chutes)
Molded
Case Frame
TerminalsSlide5
Trip Unit (not shown) detects overcurrent condition – triggers release of contacts
Contacts are pulled through
Arc Extinguishers (Arc Chutes)
which help to confine, divide and extinguish the arc when clearing an overcurrent
Terminals
typically rated 60/75 deg C
Thermal-Mag CB Construction
Handle or
Operating
Mechanism
Contacts
Arc
Extinguishers
(Arc Chutes)
Molded
Case Frame
TerminalsSlide6
Thermal-Magnetic CB Trip UnitSlide7
Trip Unit – Thermal
Overload - Bimetal element deflects and contacts trip bar which releases contacts.
Thermal-Mag CB Trip Unit - OperationSlide8
Trip Unit - Magnetic
Short Circuit - magnetic element’s electric field attracts trip bar armature and releases contacts.
Thermal-Mag CB Trip Unit - OperationSlide9
Molded Case Circuit Breaker (MCCB) Ratings
Voltage Rating:
NEC 240.83(E) & 240.85 cover circuit breaker voltage marking and basic requirements
AC assumed, Verify if rated for DC
Slash ratings (such as 120/240 or 480/277) can only be used on solidly grounded systems where the voltage to ground does not exceed the lower rating and the voltage between any
two conductors
does not exceed the higher
rating
Corner-grounded, resistance-grounded & ungrounded systems require “straight” rated
circuit breakers (240, 480 or 600)
2-pole CBs on corner-grounded systems require special ratings and must be marked “1 phase - 3 phase” Slide10
MCCB Ratings
Ampere Rating:
80% rated unless marked and applied in equipment for 100% rating - Typically rated up to 2500A
Interrupting Rating:
AC assumed unless marked, verify DC ratings with manufacturer
Interrupting rating varies, dependent upon voltage and manufacturer - Typical values - 10, 14, 18, 22, 25, 30, 35, 42, 50, 65, 100, 125, 200 kA.
MCCBs
applied on
corner-grounded, resistance (impedance) grounded, and ungrounded
systems may have lower
interrupting capabilities.Slide11
MCCB Types
Branch-Circuit
MCCBs:
Thermal-Magnetic and Electronic Trip
Current-Limiting and non-Current-Limiting
Listed and Recognized (mag-only MCPs for motor circuits) to UL 489Slide12
Thermal-Magnetic CB
Known as inverse time circuit breakers
Higher the current, faster it trips
Sustained overload may take may seconds to trip
Short-Circuit will cause the CB to open instantaneously and may take ½ to 1 cycles to clear the short-circuit
Instantaneous setting can be fixed or adjustableSlide13
Thermal-Magnetic CB – Instantaneous Trip
Fixed Instantaneous Setting
20A CB have fixed instantaneous setting of approximately 8 times the ampere rating.
Adjustable Instantaneous Setting
Typically 5-10 times the ampere rating.
Figure shows 100A CB
Setting of 5X = 500A = I.T.
Setting of 10X = 1000A = I.T.Slide14
Similar internal construction as thermal-magnetic circuit breaker.
Adjustable Trip Settings:
Long time pick-up (LTPU)
Long time delay (LTD)
Short-time pick-up (STPU)
Instantaneous
Override (may be fixed)
Short-time delay (STD)
Settings may include Ground Fault
Electronic Trip CBSlide15
Current Limiting CB
Similar to thermal-magnetic circuit breakers with
addition
of
current-limiting capabilities
Current limitation provided by blow-apart contacts, a fusible
limiter or
additional arc extinguishersIncreased interrupting ratings up to (200 kA) Current limiting circuit breakers limit the damage to downstream components for short circuits within their current limiting rangeSlide16
Motor Circuit Protector (MCP)
MCPs are mag-only circuit breakers.
MCPs
typically cannot be used to replace a thermal magnetic or electronic trip circuit breaker (unless in a motor circuit with a starter that is listed for use with the MCP) – NEC 430.52(C)(3).
A Mag-only (MCP)
trip
curve is
compared to a thermal-magnetic CB at the rightSlide17
Supplementary Protectors
Supplementary Protectors
Recognized to U.L. 1077 and limited per NEC 240.10.
Cannot
be used as a branch circuit protective device
(in
place of a UL 489 circuit
breaker). For supplemental protection of an appliance or other electrical equipment where branch circuit overcurrent protection is already provided, or is not required. Low interrupting ratings. Typically can be applied only on solidly grounded systems.
Most are short-circuit tested with fuses or a circuit breaker upstream and
must therefor be applied in series with an upstream fuse or circuit breaker.Slide18
Insulated Case (ICCB)
Larger physical size and amp ratings
Typically rated up to 5,000A with interrupting ratings
up to
100,000A or more
Electronic Trip
Units
Short-time delay optionsInstantaneous OverridesSlide19
Low Voltage Power Circuit Breaker (LVPCB)
Typically used in industrial facilities where selective coordination, circuit breaker maintenance, and drawout capability are required
.
Short-time delay option available without an instantaneous override, provides improved selective coordination capabilities.
Drawout capability means that these circuit breakers can be racked in and out of the
switchgear
for inspection and maintenance.
Utilize two-step stored energy operating mechanismOpening and closing springsOpening springs are charged when LVPCB is closed
Open-Close-Open operation without recharging
Close & Open is typically 5 cycles or lessAmp ratings up to 4,000A with interrupting ratings up to 200,000 amperesSlide20
LVPCBs
May be required upstream of MCCBs and ICCBs (which have instantaneous trips or overrides) for
selective coordination
capabilities
Can "hold-in" on faults for up to 30 cycles (.5 seconds) in order to achieve coordination with downstream devices
Typically equipped with adjustable electronic trip units with STD and without instantaneous override
Downstream components may need increased short-circuit current (withstand) ratingsSlide21
Fuse Basics
A “fusible” link or links encapsulated in a tube and connected to contact terminals.
Resistance of the link is so low that it simply acts as a conductor.
Can be single-element or dual-element construction
During an overcurrent the fusible link melts and opens the circuit to protect conductors and system
components from further damage. Slide22
Fuse Construction
Dual Element Time-Delay
Designed to be sized close to load and accommodate motor and transformer inrush which could not be accomplished by single-element non-time-delay or fast-acting fuses.
Overload (time delay) Element
Short Circuit (current limitation) ElementSlide23
Overload Operation
Dual Element Time-Delay
Under
a sustained
overload condition,
the spring
operated trigger assembly separates the “connector” from the short-circuit element, opening the circuit.Slide24
Short-Circuit Operation
Dual Element Time-Delay
Under a short-circuit condition, restricted portions of the short-circuit element melt and arc to burn back the resulting gaps until the arcs are suppressed by the arc quenching material and increased arc resistance.Slide25
Branch-Circuit Fuse Ratings
Branch-circuit fuse holders prevent installation of fuses that cannot provide a comparable level of protection.
When installed in rejection style clips, current-limiting branch circuit fuses cannot be replaced with fuses
that
are not current-limiting, have lower voltage ratings or higher current ratings than the
fuseholder
.
Branch-circuit characteristics include:10,000A Minimum Interrupting Rating up to 300,000A
125V AC Minimum Voltage Rating
NEC 240.60(C) covers required fuse voltage marking.NEC 240.60(A)(2) permits 300V cartridge fuses to be used on single-phase 277V lighting circuits.
NEC 240.61 allows fuses rated 600V or less to be used for voltages below their rating.Slide26
Branch-Circuit Fuse Classes
Fuse classes and UL/CSA/ANCE standard governing performance and characteristics include:
Class L – UL/CSA/ANCE 248-10
Class H – UL/CSA/ANCE 248-6,
& 7
Class K – UL/CSA/ANCE 248-9
Class RK1 & Class RK5 – UL/CSA/ANCE 248-12
Class J – UL/CSA/ANCE 248-8
Class T – UL/CSA/ANCE 248-15
Class G – UL/CSA/ANCE 248-5Class CC – UL/CSA/ANCE 248-4
Class CF - UL/CSA/ANCE 248-17Slide27
Class L
600V AC, 601A up to 6000A
Amperage case sizes include:
800, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000
200kA Interrupting rating or higher
Time-delay or fast-acting
Time-delay typically 500% for 4 or 5 seconds
Current limitingRejection feature – class
and size rejecting
Applications:Main or large feeder circuitsMixed loads (time-delay)
Motor or transformer loads (time-delay)Slide28
Class H/K Fuses
250V AC or 600V AC, up to 600A
Amperage case sizes include:
30, 60, 100, 200, 400, 600
Interrupting rating is only 10 kA for Class H fuses, 50 kA to 200kA for Class K5 fuses.
Non-time delay or time-lag
These fuses are dimensionally the same as the Class R fuses, however, they do not have the rejection feature.
Renewable Fuses or One-Time Fuses
They are general purpose fuses for general applicationsSlide29
Class RK1, RK5
250V AC or 600V AC, up to 600A
Amperage case sizes include:
30, 60, 100, 200, 400, 600
200kA Interrupting rating or higher
Time-delay or fast-acting
Current limiting - RK1 more current-limiting than RK5
Rejection feature – prevents replacement of Class R fuses with Class H fuses - Notch in ferrule (for cartridge fuses) or blade
Applications:
Branch, feeder circuits Motors & transformers (time-delay)Slide30
Class J
600V AC, up to 600A
Amperage case sizes include:
30, 60, 100, 200, 400, 600
200kA Interrupting rating or higher
Time-delay or fast-acting
Current limiting
Rejection feature – class
and size rejecting
Space saving design compared to Class RApplications:Branch, feeder circuits
Motors & transformers (time-delay)Slide31
Class T
300V AC or 600V AC, up to 1200A
Amperage case sizes include:
30, 60, 100, 200, 400, 600, 800, 1200
200kA Interrupting rating
Fast-acting
Current limiting
Rejection feature – class
and size rejectingBest space saving design of any power fuseApplications:
Heating and lighting circuits277V single phase lighting circuits (300V fuses)Residential and multi-meteringSlide32
Class G Fuses
600V AC, up to 20A
480V AC, 25-60A
Amperage case sizes include:
15, 20, 30, 60
100kA Interrupting rating
Time-delay (6 to 60 amperes)
Current limitingRejecting feature
Length of fuse varies with the amperage
Applications: Small motors & transformers General applicationsSlide33
Class CC Fuses
600V AC, up to 30A
200kA Interrupting rating
Fast-acting or time-delay
Current-limiting
13/32” Diameter, 1-1/2” Length
Grooved ferrules provide rejection feature
Applications:
General purpose
Street lighting, lighting ballasts, heating, motor control circuits (fast-acting)Small motors or transformer circuits (time-delay)Slide34
Supplemental Fuses
Fuses can have many voltages and interrupting ratings within the same case size.
Interrupting ratings range from 35 to 100,000 A
Examples of supplemental fuses are ¼” X 1¼ ”, 5 X 20 mm, and 13/32” X 1½” fuses
Supplemental fuses can only be used where proper protection is already being provided by a branch circuit device or if protection is not required. Slide35
Cable Limiters
NEC 230.82(1) allows the application of cable limiters on the supply side of the service disconnect.
The application of cable limiters on the supply side of service-entrance conductors provides:
Short-circuit, current-limiting protection for downstream equipment
Decreased possibility of severe equipment damage or burn-down against high short-circuit currents.
Isolation of one or more faulted conductors.
Only the cable limiters in the faulted conductors open, other conductors remain in operation.
Helps keep
the service in operation and continuity of service is improved. Slide36
High Speed Fuses
Typically used for protection of drives, SCRs or sensitive electronic equipment
Very Current-limiting
NEC 430.52(C)(5) permits the use of high-speed fuses in power electronic devices in solid-state motor controller system if replacement fuses are marked adjacent to the fuses.
High-Speed Fuses
Required for protection
of VFD – Replacement
fuses must be marked
M
Replace with:
Bussmann
FWH-400A
VFDSlide37
GFCI Protective Devices
Ground-Fault Circuit Interrupter (GFCI)
Article 100 defines a ground-fault circuit interrupter as a device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a Class A device.
Note: Class A ground-fault circuit interrupters trip when the current to ground has a value in the range of 4 to 6 mA or greater.Slide38
GF Protective Devices
Ground-Fault Protection of Equipment (GFP)
Article 100 defines ground-fault protection of equipment as a system intended to provide protection of equipment from damaging line-to-ground fault currents by operating to cause a disconnecting means to open all ungrounded conductors of the faulted circuit. This protection is provided at current levels less than those required to protect conductors from damage through the operation of a supply circuit overcurrent device.Slide39
Motor Circuit Devices
Manual Motor Protectors/Starters
Sometimes called MMPs
Provide motor overload protection per NEC 430.32(A)(1) & (B)(1)
Provide controller function (On-Off) per NEC 430.83(A)(1) (HP rated & Listed to UL 508)
Provide limited amount of short-circuit protection via a magnetic trip, but
not
acceptable for branch-circuit, short-circuit and ground fault protection (NEC 430.52). Slide40
Motor Circuit Devices
Manual Motor Protectors (Cont)
If marked “Suitable as Motor Disconnect” (and lockable in the “off” position per UL 508) – can be used as a motor disconnecting means if located between the final motor branch-circuit, short-circuit and ground fault protective device and the motor (NEC 430.109(A)(6).
Typically suitable for group motor protection applications (as long as they are protected by a branch-circuit device) per NEC 430.53(D).Slide41
Motor Circuit Devices
Self-Protected Starters
Often called “Coordinated protected starters” and “Type E” starters – Listed to UL 508 as a combination Starter.
Provide motor overload protection per NEC 430.32(A)(1) & (B)(1) and motor circuit (branch-circuit) protection per NEC 430.52(C)(6), by combining a magnetic short-circuit trip and adjustable motor overload in one package
.Slide42
Motor Circuit Devices
Self-Protected Starters
Provide controller function (On-Off) per NEC 430.83(A)(1) (HP rated & Listed to UL 508) and permitted as the motor disconnecting means per NEC 430.109(A)(5).
Many have slash voltage ratings and can only be applied on solidly grounded systems where the voltage to ground does not exceed the lower of the two ratings and the voltage between any two conductors does not exceed the higher of the two ratings.Slide43