AN2064 - APPLICATION NOTE

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Table 2: Telcordia GR1089 AC power fault test

Using series overcurrent protection, two technologies are available, PTCs and fuses.

PTCs are resistive elements that dissipate power when subjected to current, increasing their temperature

and making their resistance quickly increase (10

Ω @ 25°C and 100kΩ @ 150°C for example). The nice

feature of the PTCs is that they are resettable but they have two main drawbacks. The first drawback is

its resistance and, as already mentioned, some applications like digital networks do not allow resistive el-

ements. The second drawback is linked to its tolerance, which makes it difficult to achieve line equilibrium

(longitudinal balancing).

Fuses do not have these resistive drawbacks, making them well suited for digital applications.

From the previous discussion we can conclude that the fuse must withstand first level surges for US (or A

criterion for Europe) but may operate for second level surge (or B criterion). As far as the US market is

concerned the fuse has to remain operational for the 10/1000µs 1kV 100A and the 2/10µs 2.5kV 500A

First Level AC Power Fault Test

Test

Applied Voltage, 60Hz

Short Circuit Current

Duration

1

0.33A

15 minutes

2

0.17A

15 minutes

3

1A at 600V

60 Applications, 1 second each

4 (*)

1A

60 Applications, 1 second each

5

NA

NA

60 Applications, 5 second each

6

0.5A

30 seconds each

7

2.2A

5 x 2 seconds each

8

3A

5 x 1.1 second each

9 (*)

5A

0.5 second each

Second Level AC Power Fault Test

1

25A

15 minutes

2

60A

5 seconds

3

7A

5 seconds

4

2.2A at 600V

15 minutes

(*) Primary protector in place (MDF)