Surge Tolerant Fuses
1) Note:
Testing: Introduction
With a charge voltage of UC = 1000 V, the standardized
pulse generator in Fig. 1 supplies a maximum pulse current Ipuls
= 67 A, providing the current limiting resistor is
Several standards have been established for the Telecom
industry, all of which are aimed at combining the interference
influences of Lightning Surge, Power Induction and Power
Contact, together with the associated safety aspects, and to
derive suitable testing methods for the components
in question.
RD = 0Ω. The shunt RM for the current monitoring has a very
low resistance and has therefore no notable influence to the
current amplitude. This means that the data sheet current
67 A (1) does not represent the maximum permissible pulse
amplitude of the fuse in question, but the maximum current
amplitude which can be supplied by the pulse generator. If a
max. current higher than 67 A is to be expected in a circuit, the
I2t-values of the fuse can be calculated using the formula I2t =
0,72 x i2peak x t2, as a good approximation in order that the
selected fuse can accept the expected current pulse without
interrupting the circuit.
Various kinds of loads have been defined and standardised
as testing criteria. They can be simulated with the aid of an
appropriate test circuit. This provides circuit designers with the
facility for optimally adapting the stages of a protection circuit to
one another.
Current relevant standards are:
ITU-T K.20
International Telecommunication Union,
Standardisation Sector of ITU
Power induction: Test circuit
Fig. 2
Test:The fuse in the test circuit AC 300 V / 50 Hz is loaded 5
UL 1459/1950 Standard for Safety, Telephone Equipment
(USA)
GR 1089 Core Bell Communications Research (USA)
200 ms 60 s
200 ms
Tests :
60 s
Schurter fuses have been tested according to the following
standards and testing criteria(this list is not exhaustive):
600 Ω
1. ITU-T K.20
Lightning Surge: Test circuit
Fig. 1
Fuse
I
R
puls
D
I
eff = 0,5 A
15 Ω
0,2 µF
+
20 µF
Fuse
times with Ieff = 0,5 A for 200 ms at intervals of 60 sec.
Requirement: The fuse shall not interrupt the circuit.
50 Ω
R
M
Power Contact: Test circuit
Fig. 3
Test: The fuse in the test circuit AC 250 V / 50 Hz is loaded with
the current value ISC stated in the data sheet. The supply
Pulse current
Generator no-load
15 Min.
50%
R
D
t
t1=10µs
t2=700µs
Fuse
Test:
1. The pulse amplitude (generator no-load) is set to 1000 V
and the pulse shape to 10 µs / 700 µs.
I
sc
2. The pulse current Ipuls is set to the value Ipuls max. stated in
the data sheet with limiting resistor RD.
voltage is maintained for 15 minutes.
3. Test mode : 10 single pulses, at an interval of 60 sec.
alternating polarity.
Requirement: The fuse shall interrupt the circuit.
Requirement: The fuse shall not interrupt the circuit.
160
Schurter, Inc. • Phone 707-778-6311 • Fax 707-778-6401 • E-mail: info@schurterinc.com • Website http://www.schurterinc.com
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