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Suggestion on How to Use
Suggestion on How to Use

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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

Component ProtectionSlide3

Component Protection

Electrical system components must be applied within their short-circuit current ratings.

Electrical system components can be destroyed if the overcurrent devices do not limit the short-circuit current to within the short-circuit current rating of the system’s components.

NEC 110.10

covers protection of electrical system components.Slide4

Component Protection

NEC 110.10

– Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics.

“The overcurrent protective devices, the total impedance, the

equipment short-circuit

current ratings, and other characteristics of the circuit to be protected shall be so selected and coordinated

to

permit the circuit protective devices used to clear a

fault to do so

without

extensive

damage to the electrical

equipment

of the circuit.”

The specified OCPD must

protect

the electrical components/equipment from damage under short circuit conditions.Slide5

Component Protection

NEC 110.10

– Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics.

“This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the equipment grounding conductor(s) permitted in 250.118.”

The equipment must be protected for the various types of potential faults, including phase to phase, phase-to-ground, phase-to-neutralSlide6

Component Protection

NEC 110.10 - Component Protection

“Listed

equipment

applied in accordance with their listing shall be considered to meet the requirements of this section.”

The

testing

requirements of electrical components

must be understood

to assure proper application and protection.Slide7

Component Protection

Component

short-circuit current ratings

depends

upon:

Amount of fault current (RMS sym. short-circuit current, and in some cases, peak let-through current) and length of time, or

I

2

t Withstand Ratings

These values have been established through short-circuit testing of

the components.

 

If both the let-through currents (I

RMS

and I

p

) and the time it takes to clear the fault, or the let-through I

2

t, of the current-limiting overcurrent protective device are less than the withstand rating of the electrical component, then that component will be protected from short-circuit damage.

Slide8

Component Protection

The following components can be analyzed by establishing the short-circuit withstand data of each component and then selecting the proper overcurrent protective device:

Wire/Cable

Bus (Busway, Switchboards, Motor Control Centers and Panelboards)

Low Voltage Motor Controllers

Transfer SwitchesSlide9

Conductor Protection

Proper protection of

conductors

will improve reliability and reduce the possibility of injury.

Overcurrent devices must limit the short-circuit current to within the short-circuit current rating of the

conductor.

Merely matching the ampacity rating of the

conductor

with the ampere rating of a protective device may not assure component protection of the

conductor

under short-circuit

conditions, especially when the overcurrent device is sized up to 10 times the ampacity of the conductor (or even higher). Slide10

Conductor Protection

Withstand ratings for

conductors (5 sec & I

2

t):

ICEA - Insulation Damage (150

Deg

C)

Soares

- Cable to become loose under lug (Annealing point of copper - 250

Deg

C)

Onderdonk

- Melting of Cable (1,083

Deg

C)Slide11

ICEA Chart

Short Circuit Withstand Chart for Copper

Conductors

with Thermoplastic insulation

Allowable Short Circuit Current Based on Clearing Time and

Conductor

Size

Based on physics formulaSlide12

Conductor Protection

ICEA insulation damage

tables

Maximum Short Circuit Withstand Current (A)Slide13

Overcurrent Device Selection

The next step to analyzing protection of conductors against short circuits depends upon the overcurrent device selected and available fault current

The overcurrent protective device used to protect the conductor can either be a current limiting fuse or circuit breaker (current limiting or non-current limiting).

Slide14

Conductor Protection

The circuit shown originates at a distribution panel where 40,000 amperes RMS symmetrical are available.

The 10 AWG THW copper conductor is protected against short-circuits by a 60A Class RK1 fuse.

Short-Circuit

60A Class RK1 Fuse -

LPS-RK60SP

LOW-PEAK

® Dual-Element Fuse

40,000A

RMS Sym.

Available

460V, 3

Ø

20HP

10 AWG THW CopperSlide15

Conductor Protection

10 AWG conductor short circuit withstand is 4,300A for one cycle (based upon ICEA).

The OCPD (LPS-RK-60SP) must limit the 40,000A RMS fault to 4,300A and clear within one cycle or less in order to properly protect the 10AWG conductor.

The LPS-RK-60SP let-thru chart

shows

: that a 40,000A fault is reduced to 3,000A (w/in 1/2 cycle)

Since the amount of current

let-through by

the fuse is less

than the short-circuit

withstand

for the given

period of time,

the conductor is

protected.Slide16

Busway Protection

Available Fault current equals 65,000A

With KRP-C800SP ampere LOW-PEAK® fuses, the 65,000A available fault will be reduced to 19,000 A (from the let-through charts).

This would allow a standard 22,000 ampere RMS symmetrical (3-cycle) rated bus.

Short-Circuit

800 Amp Plug-in Bus

KRP-C800SP 800 Amp LOW-PEAK

Time-Delay Fuses

Bracing Required?

65,000A

RMS Sym.

Available

800A SwitchSlide17

Protection of Bus

U.L. Standard 891 (Switchboards) and U.L. 67 (panelboards) detail short-circuit current ratings for a durations of 3 cycles, unless the main overcurrent device clears the short in less than three cycles.

Motor control centers, per U.L. 845 have short-circuit current ratings for a duration of 3 cycles, unless the main overcurrent device clears the short in less than 3 cycles.

Current Limiting devices can be used for protection of the bus in these assemblies.Slide18

Protection of Bus

The top design meets 110.10 of the NEC because a 65kA fault would be cleared in ½ cycle or less and the MCC is rated for 3 cycles.

The bottom design violates 110.10 because a 65kA fault could continue for 6 cycles, but the MCC is only rated for 3 cycles.

800A

Power

CB

w/STD = 6 cycles

65,000A RMS Sym. Available

800A MCC with

3 cycle 65kA Bracing

800A Class L Fuses

800A MCC with

3 cycle 65kA Bracing

65,000A RMS Sym. AvailableSlide19

Motor Circuit Protection

M

and these motor starter contacts and O.L. relays,

With a

Fault Here,

that is cleared by this protective device,

these conductors,

… must all be rated to safely withstand the energy of the fault let-through current without “extensive damage” to any of the circuit components.

this switch

,Slide20

Motor Controller Short-Circuit Current Ratings – UL 508

UL 508 Tests motor controllers to minimum short-circuit current ratings as indicated in the table.

Higher ratings are available

At standard or higher ratings, significant, permanent damage is allowed per UL 508.Slide21

UL 508 - Industrial Control Equipment

Maximum Damage Criteria for Standard & High Fault Acceptance Criteria

All Devices

The door or cover shall not be blown open.

No discharge of parts beyond the enclosure.

Enclosure cannot become energized.Slide22

UL 508 - Industrial Control Equipment

Maximum Damage Criteria for Standard & High Fault Acceptance Criteria (

Cont

)

Motor Control Devices

The load switch function of the motor control device is able to be inoperative at the conclusion of the test.

The contacts of the motor control device are able to weld or completely disintegrate.

Overload Relays

Overload relays are

allowed

to

be burned out

.Slide23

Protection Levels –

IEC 60947-1 & UL 508E

Type 1

Considerable damage to the contactor and overload relay is acceptable

Replacement of components or a complete new starter may be needed

There must be no discharge of parts beyond the enclosure.

Enclosure cannot become energized.

Note: Similar to UL508 testing.Slide24

Protection Levels –

IEC 60947-1 & UL 508E

Type 2

No damage is allowed to either the contactor or the overload relay

Light contact welding is allowed, but must be easily separable

Testing and documentation is required to prove Type 2 Protection Slide25

Transfer Switch

Short

circuit

withstand rating

Typically defined as 3-cycles at a given magnitude of current

UL1008 now allows manufacturers to optionally test for longer periods

UL1008 short circuit withstand testing only ensures that the contacts do no weld during the test

This ensures that

the transfer

switch can transfer to the alternate source, however, it does

not

ensure that the normal contacts are viable and free of

damage

Because of this, the testing does not ensure that the transfer switch can be transferred back to the original source

Note

- Applying a transfer switch within its short

circuit

withstand rating

does NOT guarantee that the switch survives a downstream fault without damage.Slide26

Transfer Switch

Short

time

withstand rating

UL1008 allows optional testing of transfer switches to achieve

a short time withstand rating

Short time ratings are also expressed in a number of cycles at

a given magnitude of current.

The test for short time withstand is treated differently than the short circuit withstand

After the short time withstand test, the contacts must be viable.

A temperature rise test is done to verify.

Note

- Applying a transfer switch within its short

time

withstand rating

ensures the transfer switch is still completely functional after a downstream fault.Slide27

Transfer Switch

Short

circuit withstand vs. short

time

withstand

Short circuit

Short

time

Required by UL1008

Optional

Not

required by UL1008

3-cycles at rated current

(65 kA, for example)

Typically longer than 3-cycles

Contact damage

permitted

Contacts must remain viable

Switch not required

to transfer back

to normal power

Ensures

that switch can transfer

back to normal power

Manufacturer

option to test at

longer timesSlide28

UL 1008 Ampere Rating

480 V

600 V

Any Breaker

Specific Breaker

Any Breaker

Specific Breaker

Fuse

40, 80, 100

10,000

30,000

10,000

22,000

100,000

150, 200

10,000

30,000

22,000

35,000

100,000

225, 260, 400

30,000

50,000

200,000

40, 80, 100, 150, 200

30,000

50,000

22,000

35,000

200,000

225, 260, 400

30,000

50,000

50,000

65,000

200,000

600, 800, 1000,1200

50,000

65,000

50,000

65,000

200,000

1600

50,000

65,000——

200,000Transfer SwitchContactor withstand/close

-on ratings Slide29

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Suggestion on How to Use - Description

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 ID: 638690 Download Presentation

Uploaded By: trish-goza
Views: 28
Type: Public

Tags

circuit short current 000 short circuit 000 current protection withstand conductor fault ratings switch damage transfer time component device

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