Transcript Dual Element Time-Delay

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1
Types of Overcurrent Protective Devices
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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.
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3
Thermal-Mag CB Construction
Terminals
• Molded case frame
provides insulated
housing for components
Arc
Extinguishers
(Arc Chutes)
• Contacts open and close
circuit
Contacts
• Handle or Operating
mechanism opens and
closes contacts – cannot
be “teased” - quick-make,
quick break
Handle or
Operating
Mechanism
Molded
Case Frame
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Thermal-Mag CB Construction
•
•
•
Terminals
Trip Unit (not shown)
detects overcurrent
condition – triggers
release of contacts
Arc
Extinguishers
(Arc Chutes)
Contacts are pulled
through Arc
Extinguishers (Arc
Chutes) which help to
confine, divide and
extinguish the arc when
clearing an overcurrent
Contacts
Handle or
Operating
Mechanism
Terminals typically rated
60/75 deg C
Molded
Case Frame
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Thermal-Magnetic CB Trip Unit
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Thermal-Mag CB Trip Unit - Operation
• Trip Unit –
Thermal
• Overload Bimetal
element
deflects and
contacts trip
bar which
releases
contacts.
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Thermal-Mag CB Trip Unit - Operation
• Trip Unit Magnetic
• Short Circuit magnetic
element’s
electric field
attracts trip
bar armature
and releases
contacts.
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8
Molded Case Circuit Breaker (MCCB)
Ratings
•
Voltage Rating:
•
NEC 240.83(E) & 240.85 cover circuit breaker
voltage marking and basic requirements
1) AC assumed, Verify if rated for DC
2) 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
3) Corner-grounded, resistance-grounded & ungrounded
systems require “straight” rated circuit breakers (240, 480 or
600)
4) 2-pole CBs on corner-grounded systems require special
ratings and must be marked “1 phase - 3 phase”
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MCCB Ratings
•
Ampere Rating:
•
•
80% rated unless marked and applied in equipment
for 100% rating - Typically rated up to 2500A
Interrupting Rating:
1) AC assumed unless marked, verify DC ratings with
manufacturer
2) Interrupting rating varies, dependent upon voltage
and manufacturer - Typical values - 10, 14, 18, 22,
25, 30, 35, 42, 50, 65, 100, 125, 200 kA.
3) MCCBs applied on corner-grounded, resistance
(impedance) grounded, and ungrounded systems
may have lower interrupting capabilities.
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10
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 489
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Thermal-Magnetic CB
•
Known as inverse time circuit
breakers
1) Higher the current, faster it trips
2) Sustained overload may take may
seconds to trip
3) Short-Circuit will cause the CB to open
instantaneously and may take ½ to 1
cycles to clear the short-circuit
4) Instantaneous setting can be fixed or
adjustable
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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.
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13
Electronic Trip CB
• Similar internal
construction as thermalmagnetic 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
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Current Limiting CB
• Similar to thermal-magnetic circuit
breakers with addition of currentlimiting capabilities
• Current limitation provided by
blow-apart contacts, a fusible
limiter or additional arc
extinguishers
• Increased interrupting ratings up
to (200 kA)
• Current limiting circuit breakers
limit the damage to downstream
components for short circuits
within their current limiting range
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15
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 right
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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.
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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
options
• Instantaneous
Overrides
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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 mechanism
• Opening and closing springs
• Opening springs are charged when LVPCB is closed
• Open-Close-Open operation without recharging
•
•
Close & Open is typically 5 cycles or less
Amp ratings up to 4,000A with interrupting ratings up
to 200,000 amperes
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LVPCBs
1. May be required upstream of
MCCBs and ICCBs (which have
instantaneous trips or overrides)
for selective coordination
capabilities
2. Can "hold-in" on faults for up to
30 cycles (.5 seconds) in order to
achieve coordination with
downstream devices
3. Typically equipped with
adjustable electronic trip units
with STD and without
instantaneous override
4. Downstream components may
need increased short-circuit
current (withstand) ratings
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20
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.
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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 singleelement non-time-delay or fast-acting fuses.
• Overload (time delay) Element
• Short Circuit (current limitation) Element
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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.
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Short-Circuit Operation
• Dual Element TimeDelay
• Under a short-circuit
condition, restricted
portions of the shortcircuit element melt and
arc to burn back the
resulting gaps until the
arcs are suppressed by
the arc quenching
material and increased
arc resistance.
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24
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 currentlimiting, have lower voltage ratings or higher current ratings than
the fuseholder.
•
Branch-circuit characteristics include:
1) 10,000A Minimum Interrupting Rating up to 300,000A
2) 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.
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Branch-Circuit Fuse Classes
•
Fuse classes and UL/CSA/ANCE standard governing performance and
characteristics include:
1)
Class L – UL/CSA/ANCE 248-10
2)
Class H – UL/CSA/ANCE 248-6, & 7
3)
Class K – UL/CSA/ANCE 248-9
4)
Class RK1 & Class RK5 – UL/CSA/ANCE 248-12
5)
Class J – UL/CSA/ANCE 248-8
6)
Class T – UL/CSA/ANCE 248-15
7)
Class G – UL/CSA/ANCE 248-5
8)
Class CC – UL/CSA/ANCE 248-4
9)
Class CF - UL/CSA/ANCE 248-17
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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 limiting
• Rejection feature – class and size rejecting
• Applications:
• Main or large feeder circuits
• Mixed loads (time-delay)
• Motor or transformer loads (time-delay)
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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 applications
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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)
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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 R
Applications:
• Branch, feeder circuits
• Motors & transformers (time-delay)
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30
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
rejecting
• Best space saving design of any power
fuse
• Applications:
• Heating and lighting circuits
• 277V single phase lighting circuits
(300V fuses)
• Residential and multi-metering
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31
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 limiting
Rejecting feature
Length of fuse varies with the
amperage
• Applications:
•
•
Small motors & transformers
General applications
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32
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)
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33
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.
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34
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 shortcircuit 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.
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35
High Speed Fuses
High-Speed Fuses
Required for protection
of VFD – Replacement
fuses must be marked
Replace with:
Bussmann
FWH-400A
VFD
• 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.
M
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36
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 deenergize 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.
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37
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.
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38
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).
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39
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).
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40
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.
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41
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.
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