DOCA0095EN

Thermal-Magnetic Protection for Circuit Breakers

Thermal-magnetic protection provides the following features for general-purpose applications:

  • Thermal protection against overload, with fixed threshold In.

  • Instantaneous protection against short circuits, with fixed threshold Ii.

The following figure shows the trip curve.

In Thermal protection pickup

Ii Instantaneous trip point

Thermal Protection

The thermal protection pick-up value cannot be adjusted. Its value for each frame rating is shown below.

 

Frame rating In (A)

 

15

20

25

30

35

40

45

50

60

70

80

90

100

110

125

In pick-up (A)

15

20

25

30

35

40

45

50

60

70

80

90

100

110

125

AC Magnetic Trip Levels

Ii

Rated Current (A)

15

20

25

30

35

40

45

50

60

70

80

90

100

110

125

Hold (A)

400

400

400

400

400

400

400

480

640

640

800

1000

1000

1000

1000

Trip (A)

600

600

600

600

600

600

600

720

960

960

1200

1500

1500

1500

1500

DC Magnetic Trip Levels

The Time Current Curves (trip curves) provide the complete time-current characteristics of the circuit breaker when applied on an AC system. When applying thermal-magnetic circuit breakers on DC systems, they retain the same thermal tripping characteristics, but the magnetic trip levels vary. See table for the appropriate DC magnetic hold and trip levels.

Ii

Rated Current (A)

15

20

25

30

35

40

45

50

60

70

80

90

100

110

125

Hold (A)

460

460

510

510

510

510

510

510

790

900

900

1200

1200

1200

1200

Trip (A)

680

680

800

800

800

800

800

800

1240

1420

1420

1850

1850

1850

1850

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