Breakers and Fuses

BREAKERSAND

FUSESAS CIRCUIT PROTECTIVE DEVICES

Breakers and Fuses

Breakers and Fuses

Fuse Replacements

Plug Fuse Penny CartridgeFuse

CopperBar

Breakers and Fuses

RELIABLE

TAMPERPROOF

RESETTABLE

SAFE

Design Specification

Switch must be:

Breakers and Fuses

Arc Extinguisher

SidePlate

SteelPlates

Breakers and Fuses

Overall, Circuit BreakersProvide Better Protection

than Fusesfor Low Voltage

Circuit Protection

…and here’s why.

Breakers and Fuses

… Technical

The Issues

Equipment protection. Coordination. Downtime. Current limiting

fuse characteristics.- Fuse let-through chart.- Up-Over-Down Method.

Series ratings.

Short circuit capacity. Motor circuit

protectors. Single-phase

protection. High/low level

fault protection.

Breakers and Fuses

Short Circuit Calculations

Unlimited Fault Current

2,500 kVA, Z=5.75%

Calculated Fault 52,296A

12,470V

480Y/277V

Isc = = = 52,296AkVA 2,500 x 1,000 x 100

VxZ 480 x 3 x 5.75

Breakers and Fuses

Secondary Short Circuit Capacity ofTypical Power Transformers

3005%

5005%

7505.75%

10005.75%

15005.75%

20005.75%

25005.75%

208 Volts, 3-Phase 240 Volts, 3-Phase 480 Volts, 3-PhaseTransformer Maximum Rating 3-Phase Short CircuitkVA and kVA Available

Impedance from PrimaryPercent System

Short Circuit Current rmsSymmetrical Amps

Combined Transformer and Motor

Unlimited 18400 17300 8600

Unlimited 30600 28900 14400

Unlimited 40400 38600 19300

Unlimited 53900 51400 25700

Unlimited 80800 77200 38600

Unlimited 51400

Unlimited 64300

Breakers and Fuses

1500 kVA Transformer/5.75% Impedance/480 Volts

Distance in Feet from Transformer to Breaker Location

5000200010005002001005020105200

60

50

40

30

20

10

UTILITY KVA500,000

4 - 750 MCM2 - 500 MCM250 MCM#1/0 AWG#4 AWG

Fau

lt C

urre

nt in

Tho

usan

ds o

f A

mpe

res

(Sym

.)Effects of Impedance

Breakers and Fuses

Short Circuit CalculationsUnlimited Fault Current

2,500 kVA, Z = 5.75%

Calculated Fault

12 Feet, 3,200A Copper Feeder Busway

3,200A

3,200A Bus

12,470V

480Y/277V

60 Feet(3) 1-Conductor#4/0 CopperTHW InsulationSteel Conduit

200A 200A 150A 100 Feet(3) 1-Conductor#2 CopperTHW InsulationSteel Conduit

Bus Plug

Note:Obtain specific impedancevalues for each system.Do not assume the valuesshown here will be typical.

MainControlPanelCalculated at 100% Motor Contributions

10,968

29,560

64,328

52,296

Breakers and Fuses

Bolted Fault Arcing Fault

Systems must be designed However, the majority of faultsfor worst case conditions. will be arcing type.

Line-to-Line-to-Line Fault

Breakers and Fuses

Frequency of Faults

Least Likelihoodof Fault

Greatest Likelihoodof Fault

UTILITY

M M

Breakers and Fuses

Frequency of Faults

TYPE OF FAULTS INCIDENCE % FAULT MAGNITUDE

Three-phase bolted ? Approaches fault available

Single-phase bolted 5% 30-60% of fault available

Line-to-line arcing 15% Low to medium (less than 30%)

Line-to-ground arcing 80% Very low to low (less than 10%)

Breakers and Fuses

Control Panel

Breakers and Fuses

Time

Current

Starting Curve

Typical MotorCapability Curve

LockedRotor Time

Motor Circuit Protectors (HMCP)

Breakers and Fuses

Single-Phase Protection

Single-phasing on three-phase loads cannot occur with circuit breakers as all three poles open on a single-phase fault.

Single-phasing on motor loads when a single fuse blows can cause heating and eventual damage to motor windings.

To eliminate single-phasing when usingfuses is both costly and inefficient.

Low level arcing faults can continue to be fedthrough the load.

Breakers and Fuses

Single-Phasing Condition

A

BC

Protective Device Starter

10A

10A

10A

Motor

“Normal Condition”

Dual Element Fuse

A

BC Fault

18A

0

18A

10A x 180%

10A x 180%

Motor

A

B

C

Pha

se

Clears after multiple cycles.

CLEARING TIMEFOR A LOW LEVEL FAULT

ABC

Motor Circuit Protector (MCP)

Fault

0

0

0

Motor

A

B

CClears in less than one cycle.

Pha

se

Breakers and Fuses

High/Low Level Fault Protection

Circuit breakers will clear high level(short circuit) faults safely and effectively.

Circuit breakers in general will clear low level (overload) faults more effectively than fuses (e.g., a motor circuit protector will clear a low current motor fault (X6) in a shorter time than a fuse). Plus prevent single-phasing.

Circuit breakers can include ground fault protection. They quickly interrupt dangerous ground faults before they escalate.

Breakers and Fuses

IEC 947-4-1 defines two levels of coordination for the motorstarter under short circuit conditions.

TYPE 1 COORDINATION

Under short circuit conditions, the contactor or starter shall cause no danger to persons or installation and may not be suitablefor further service without repair and replacement of parts.

TYPE 2 COORDINATION

Under short circuit conditions, the contactor or starter shallcause no danger to persons or installation and shall be suitablefor further use. The risk of contact welding is recognized, inwhich case the manufacturer shall indicate the measures tobe taken in regards to equipment maintenance.

Equipment Protection

Breakers and Fuses

FACTS

Type 1 coordinated motor branch circuits are capableof clearing low level faults without damage.

Type 1 may not prevent damage to the motor starter components in high level faults.

Type 2 does not permit damage to the starter (as noted).

Type 1 or Type 2 does not cover protection of the motor.

Breakers or fuses may be utilized in Type 1 or Type 2.

Type 2 prohibits replacement of parts (except fuses).

Most faults in electrical systems are low level.

Fuses can nuisance trip on startup under Type 2.

Equipment Protection

Breakers and Fuses

CHOICES

Type 1 Must replace heaters.May need to replace

starter.

Type 2 with fuses Must replace fuses.

Type 2 with breaker No replacement required.

Reduction in downtime is critical to manufacturing facilities.

Type 2 intended to keep production running.Repair or replacement is recommended.

Equipment Protection

Breakers and Fuses

Why do we have molded case, insulatedcase and metal enclosed breakers? Molded

CaseCircuitBreakers

InsulatedCaseCircuitBreakers

Metal EnclosedAC PowerCircuitBreakers

Westinghouse Series CMolded Case Circuit Breakers70A - 2,500A

Westinghouse SPB SystemsPow-R Circuit Breakers200A - 5,000A

Westinghouse Types DSII/DSLIILow Voltage AC PowerCircuit Breakers100A - 5,000A

Breakers and Fuses

Time-Current Curve Coordination StudyA B C D EMOTOR

Ansi 3-PhaseThrough FaultProtectionCurve(MoreThan 10In Lifetime)

TransformerInrush

A B

GroundProtection

PhaseProtection

.5 1 10 100 1,000 10,000.01

.1

1

10

100

1,000

Scale X 100 = Current in Amperes at 480 Volts

Tim

e in

Sec

onds

M

A

B

C

D

E

4.16 kV 250 MVA

250A

19,600A

1,600A

1,000A

20,000A

175A

100 HP-124A FLC

= Available fault current including motor contribution.

24,400A

1,000kVA5.75%

4,160 V 480Y/277 V

Breakers and Fuses

Electronic Trip Unit

Zone SelectiveInterlocking- Short Time Delay

- Ground FaultTime Delay

- InstantaneousTrip Regardlessof Short TimeDelay

- MinimizeDamage

Zone 1

Zone 2

Zone 3

Ground Fault Setting:1,200A Pickup0.5 Sec. Time Delay

Ground Fault Setting:600A Pickup0.3 Sec. Time Delay

Ground Fault Setting:300A PickupNo Time Delay

Zone Interlock Wiring

LOAD

Fault 2

Fault 1

Breaker 1

Breaker 2

Breakers and Fuses

Coordination Fuses coordinate well between each other as

the 2:1 ratio of the current rating is maintained.

Circuit breakers with thermal magnetic trip units will also coordinate well under the same conditions.

Circuit breakers with adjustable electronic tripunits will coordinate below the 2:1 ratio. Trip unit settings need to be determined by carrying outa coordination study.

Fuses cannot do zone selective interlocking.

Breakers and Fuses

Coordination

Circuit breaker flexibility.

- Adjustable pickup settings give improvedcurrent coordination.

- Adjustable time delay setting gives improvedtime coordination.

- Zone selective interlocking.• Improving time coordination.• Reducing damage to equipment.• Reducing stress on upstream devices.

Breakers and Fuses

The Issues

…Technical …The Advantages of Using Breakers

Resettable and reusable devices.

Better coordination.

Closer equipment protection.

Early warning (alarms).

No time lost in searching for replacement fuses.

Plus ground fault option.

Downtime

Breakers and Fuses

Downtime

M

Main with Ground Fault

Feeders withoutGround Fault

Control Panel

Breakers and Fuses

Current Limiting

I2t = (IRMS)2t

PeakLet-ThroughCurrent (Ip)

IRMS

rmsLet-ThroughCurrent(Calculated)

TotalClearing Time

t

tmelt tarc

Ip

AvailableShort CircuitCurrent

Breakers and FusesT

hous

ands

Ten

Tho

usan

ds

Hun

dred

Tho

usan

ds

Fuse Let-Through Chart

AvailableFaultCurrent

Let-ThroughCurrent

45 kA

40 kA

32 kA

30 kA

600A600A 600A 600A

100 kA 65 kA 35 kA 30 kA

X/R Ratio = 6.6

Fuses Tested at 15% Power Factor

Available Current in rms Symmetrical Amperes

Max

imum

Ins

tant

aneo

us P

eak

Let-

Thr

ough

Am

pere

s

Thousands Ten Thousands Hundred Thousands

CurrentLimitingThreshold 600A Fuse

BIp = 2.3 x IRMS SYM

1 5 10 5 10 5 101

5

10

5

10

5

10

Breakers and Fuses

Up-Over-Down Method100 kAAvailableFaultCurrent

200AFuse

Let-ThroughFaultCurrent

Available Current in rms Symmetrical Amperes17 kA 100 kA

Fuses Tested at15% Power Factor

X/R Ratio = 6.6

This methodassumes thatthere is nodownstreamfast actinginterruptingdevice.

CurrentLimitingThreshold

200A Fuse

Ma

xim

um

In

sta

nta

ne

ou

s P

ea

k L

et-

Th

rou

gh

Am

pe

res

Th

ousa

nds

Te

n T

hou

sand

s

H

und

red

Th

ou

san

ds

Thousands Ten Thousands Hundred Thousands

BIp = 2.3 x IRMS SYM

1 5 10

5 10 5 101

5

10

5

10

5

10

Breakers and Fuses

Breaker Contacts

Standard Contact

Current LimitingContact (Reverse Loop)

Breakers and Fuses

Current Limiting Fuse Characteristics

Stand alone current limiting fuse. Fuse is current limiting and clears

the fault in the first 1/4 cycle.

Current limiting fuse with modernfast acting circuit breakers. Breaker begins to open.

Breaker tries to clear the fault.

Dynamic impedance is introduced.

The current limiting fuse thenbecomes a slow acting device.

FuseAction

FAST

SLOW

FuseAction

FAST

SLOW

Breakers and Fuses

The Circuit Breaker Sees the FaultBefore the Fuse

…Therefore, the Up-Over-Down Method DOES NOT WORK because it’s only a theoretical calculation.

NEC requires that fuse/breaker series combinations must betested per UL test procedures.

One test is better thana million calculations.

FuseAction

FAST

SLOW

Breakers and Fuses

Fuse manufacturers have acknowledged that theUp-Over-Down MethodDOES NOT WORK withtoday’s modern highinterrupting circuit breakers.

Breakers and Fuses

Three Types of Systems

1. Selectively Coordinated System

2. Fully Rated System

3. Series Rated System

Breakers and Fuses

This system allows or selects the breaker closest to the overcurrent source to open, thus most closely isolating the problem.

CONTINUITY OF SERVICE

PROTECTION

COST

1. Selectively Coordinated System

High continuity.

All breakers fully rated.

Most costly of all three systems.

Breakers and Fuses

2. Fully Rated System

In this system, all of the breakers must be fully rated for thesystem’s available fault current. This allows for quick selectionof equipment, but allows for less continuity of service in general.

CONTINUITY OF SERVICE

PROTECTION

COST

Lower than selectively coordinated system. Usually higher than series connected system.

All breakers fully rated.

Lower than selectively coordinated system. Usually higher than series rated system.

Breakers and Fuses

3. Series Rated SystemThis is a system of series connected breakers which havebeen tested in combination and shown to effectively protect the system. Downstream breakers are not fully rated for the system’s available fault current but the upstream breaker, which is testedin combination, protects the downstream breaker by operatingbefore damage occurs.

CONTINUITY OF SERVICE

PROTECTION

COST

Continuity of service may suffer.

Downstream breakers not fully rated.

Usually the least costly system.

Breakers and Fuses

Fuses Circuit Breakers

FULLY RATED SERIES RATING

Series ratings can Circuit breakers are not be done with fuses- tested as a component and

there’s no advantage. tested in an assembly.

Series Ratings

100 kA

100 kA

100 kA

100 kA

100 kA

100 kA

100 kA

100 kA

100 kA

14 kA

14 kA

14 kA

14 kA

14 kA

14 kA

14 kA

14 kA

65 kA

Breakers and Fuses

… Practical

The Issues

Safety. Monitoring and

communications. Testability. Accessorization.

Size. Economics. Cost.

Breakers and Fuses

The Issues

Safety

…Practical …The Advantages of Using Breakers

Breakers are dead front devices.

Fused switches have exposed live parts.

Terminal shields and end covers available.

Fuses can be easily replaced withdevices that are improper and havedifferent characteristics.

Handle mechanism allows resettabilityof breaker without needing access.

Breakers and Fuses

…Practical …The Advantages of Using Breakers

The Issues

Monitoring andCommunications

Many functions can be integralto electronic trip units.

- Earth leakage/ground fault.

- Monitoring functions.

- Metering.

- Energy.

- Power factor.

- Communications.

Breakers and Fuses

The Issues

Testability

…Practical …The Advantages of Using Breakers

Electronic trip units are field testable.

Fuses are not field testable.

Push to test in the field.

Verify each unit off the assembly line.

Breakers and Fuses

…Practical …The Advantages of Using Breakers

The Issues

Accessorization Accessories are difficult to apply to fuseswitches and are very costly.

Both internal and external circuit breaker accessories are easy to install and arecost effective.

Internal.- Shunt trip. - Auxiliary

contacts.- Undervoltage release. - Bell alarms.

External.- Motor operators. - Interlocks.- Handle mechanisms. - Cylinder locks.

Breakers and Fuses

…Practical …The Advantages of Using Breakers

The Issues

Size Smaller devices allow for more room in an assembly.

Assemblies with fusible devices are larger.

Space saving in control panel.

Breakers and Fuses

Practical Issues Space and Cost Comparisons

SAVINGS… 59% Wall Space

Equipment CostSavings

Installation Time

Cost of Fuses andLabor for Replacement

Downtime

69% Floor Space

WallSpace

FloorSpace

400A KD400A KD

400A KD400A KD

1200A ND

PRL 4BBreaker

PRL 4F Fusible

$1,410 Additional for FusesPLUS Spares

9 Sq. Ft.2.83 Sq. Ft.

1200AFDP

VERT.

400AFDPW

400AFDPW

Thru-FeedLugs

400AFDPW

400AFDPW

11.3” 18”

90”73.5”

36” 72”

Breakers and Fuses

…Practical …The Advantages of Using Breakers

The Issues

Economics

Cost

No spares required. Fuses need to be replaced. Breakers are more electrically efficient.

(Fuses have a higher wattage dissipation.)

Less downtime. Less contractor labor to handle and install. $ $ saved in floor and wall space. Saves panel space.

Breakers and Fuses

Why Use a Breaker in a Distribution System:Prevents single-phasing.Motor protection.Coordination.Zone interlocking.Resettable.Dead front, no exposed parts.Space savings.Prevents downtime.Accessorization.Testable.

Breakers and Fuses

Why Use a Breaker in a Control Panel:

Prevents single-phasing.Motor protection.Ground faults.Resettable.Dead front, no exposed parts.Space savings.Prevents downtime.Accessorization.Testable.