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UDC 629.13.01 : 621.316.923
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IS0
O RG A N IZ AT1 O N FOR STAN DA RD IZATION
I N T ERN AT1 O N A L
IS0 RECOMMENDATION
R 854
REQUIREMENTS FOR 28-VOLT D.C.
FLAT STRIP FUSES FOR AIRCRAFT
1st EDITION
October 1968
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 854, Requirements for 28-volt d.c. frat strip fuses for aircraft, was drawn up
by Technical Committee ISOlTC 20, Aircraft and space vehicles, the Secretariat of which is held by the British
Standards Institution (BSI).
Work on this question led to the adoption of a Draft IS0 Recommendation.
d
In May 1965, this Draft IS0 Recommendation (No. 806) was circulated to all the IS0 Member Bodies
for enquiry. It was approved, subject to a few modifications of an editorial nature, by the following Member
Bodies :
Argentina Israel Sweden
Belgium Italy Switzerland
Japan U.A.R.
Brazil
Netherlands United Kingdom
Canada
Portugal U.S.S.R.
Chde
South Africa, Rep. of Yugoslavia
Czechoslovakia
France Spain
One Member Body opposed the approval of the Draft :
Germany
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council, which decided,
in October 1968, to accept it as an IS0 RECOMMENDATION.
v
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ISO/R 854-1968 (E)
-3-
IS0 Recommendation R 854 October 1968
REQUIREMENTS FOR 28-VOLT D.C.
FLAT STRIP FUSES FOR AIRCRAFT
1. SCOPE
This IS0 Recommendation indicates the ratings, dimensions and performance requirements for a particular range
of 28 V d.c. fuse-links for aircraft, known as flat strip fuses (by virtue of their shape). The fuse-links are
intended for use only in direct current electrical systems with a voltage not exceeding 28 V as a protection
against short-circuit faults; they are not suitable for overload protection of equipment or cables. The links,
normally constructed of a single strip element reduced in section over the fusible length and mounted in a body
of ceramic or of equally suitable material, with toughened glass window, have a limited rupturing capacity which
is related to the time constant of the circuit. It is considered important that the rated breaking capacity should be
limited to a value at which it may safely be predicted that the window will not be shattered or displaced. In
Table 1 a time constant at the location of the fuse adequate for most 28 V d.c. aircraft systems has been selected
and the maximum safe prospective current stated for this particular time constant.
2. FIELD OF APPLICATION
The fuse-links are suitable for use at any ambient temperature from -65 to +70 "C and at all altitudes from
O to 12 200 m (40 O00 ft). The time/current characteristic curves shown in the Annex are envelope curves
enclosing the characteristics of this type of link of all known manufacture. It should be appreciated that the
characteristic curves for individual fuse-links from a particular manufacturer may be within closer limits than
those shown in the Annex.
This IS0 Recommendation covers only the non-filled versions of the fuse-link.
3. TERMINOLOGY
The terminology used in this IS0 Recommendation is, as far as possible, in conformity with the International
Electrotechnical Commission (IEC) Publication 66 : Specification for fuses for voltages not exceeding I000 V
for ax. and d.c.
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-4- ISO/R 854-1968 (E
I
Dimension millimetres
inches
B
36 f 0.76 1.416 f 0.029
C 9.4 f0.4
0.375 f 0.015
D 2.4 max.
0.093 max.
E
81 f0.13 3.19 f0.005
F*
8.64 f 0.13 0.340 f 0.005
G
19 f 0.13 0.75 f 0.005
H 62 f0.13
2.44 50.005
J
22.2 f0.46 0.874 f0.018
K 3.17 f 0.4
0.125 f 0.015
For fuses of 275 A rating and above dimension F
may be 10.3 f0.13 mm (0.406 f0.005 in).
FIG. 1 - Dimensions of fuse-links
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5. TEMPERATURE AND ALTITUDE RATING
The fuse-links should be suitable for use in all ambient temperatures from - 65 to + 25 "C and at all altitudes
5.1
up to 12 200 m (40 O00 ft).
For ambient temperatures between 25 and 70 "C the fuse-link should be de-rated by 0.4 "lo of normal
5.2
rated current for every one degree increase in ambient temperature above 25 "C.
VOLTAGE, CURRENT AND BREAKING CAPACITY RATINGS
6.
The fuse-links should be suitable for use at a nominal voltage of 28 V d.c. The current rating and breaking
capacity rating should be in accordance with those listed in Table 1, page 6. The breaking capacity rating is
related to a substantially non-inductive circuit with a time constant of the value shown in Table I.
7. ENVIRONMENT
The fuse-links should comply with the requirements of IS0 Recommendation R .,* Environmental and
operational conditions of aircraft electrical equipment - Part 1 : Scope and applicability, including vibration
(other than direct engine-mounting), acceleration, crash conditions, climatic resistance and explosion proofness.
They should not support mould growth and should not deteriorate even after storage for long periods in the
tropics.
8. TEMPERATURE RISE
When the fuse-link of the rating specified in Table 1, page 6, is bolted to a cable complying with IS0 Recommen-
dation R 469, Dimensions and conductor resistance of general purpose electrical cables with copper conductors
for aircraft, using an appropriate termination and carrying rated current continuously, the temperature of the
attached cable due to the combined effects of ambient and temperature rise should not exceed the safe value of
the insulation as specified in IS0 Recommendation R 474, Perfomnce requirements for general purpose
electrical cables with copper conductors for aircraft.
At present under consideration.
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TABLE 1 - Ratings of fuse-links
(5 )
(4)
Copper core cable to be
used during tests in
accordance with
Continuous current
IS0 Recommendations
Rated breaking Duration of test
rating
R 469 and R 414
Time constant for minimum
(- 65 to + 25 OC capacity
Jrospective current) fusing current
ambient
Nominal
temperature*)
cross-sec tionaI
Cable size
area of
number
conductor
mm2
amperes seconds hours
amperes
10 5.29
35 2500
8 8.55
50 2500
6 13.6
80 3000
4 21.6
1 O0 30G0
2 33.9
130**
3000
41.5
150 3000 0.005 1
c 68
200** 3000 9 to 1.5 O0
225 0.006 O00 85
3000
O000 107
275** 3000
O000 107
325 3000
2x0 106
350** 3000
?X O0 136
400** 3000
2 x O00 170
500 3000
I
* See section 5.
* * Non-preferred ratings.
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9. TIME/CURRENT CHARACTERISTICS
The pre-arcing time/current characteristics of the fuse-links should be within the appropriate envelope curves
shown in the Annex.
10. ENDURANCE
of their normal rated current continuously at an
The fuse-links should be capable of carrying at least 80
ambient temperature of 70 OC for a minimum period of 1000 hours without deterioration.
11. IDENTIFICATION AND MARKING
Every fuse-link should be clearly and indelibly marked with its continuous current rating, the manufacturer’s
name or identification, and the number of the relevant National Standard.
4.
12. TESTS
12.1 Except where specific details are listed below, tests should be in accordance with the practice and
requirements of relevant national specifications for aircraft fuses. Evidence should be available to the
purchaser that fuse-links identical to those supplied as covered by this IS0 Recommendation have
satisfactorily passed type tests conducted in accordance with section 13.
In order that a consistent standard of quality be maintained, the manufacturer should conduct production
routine tests in accordance with section 14 and production quality tests in accordance with section 15.
12.2
The source of energy should be of sufficient power to enable the specified characteristics to be proved.
of the rated voltage, with a tolerance of + 10 The recovery voltage
The applied voltage should be 110
should be between 28 and 32 V.
12.3 Except where inappropriate, the tests should be conducted on fuse-links shielded from external draughts and
fitted with minimum lengths of 0.6 m (2 ft) of cable of rating specified in Table 1, page 6, with appropriate
terminations.
13. TYPE TESTS
13.1 F’reiiminary tests
All fuse-links subjected to type tests should first have passed the production routine tests in section 14.
The fuse-links should also be subjected to a voltage drop test.
13.2 Group tests
13.2.1 After fulfilling the requirements of the tests referred to in clause 13.1, the fuse-links should be divided
into groups for type testing as shown in Table 2, page 8. The voltage drop across the fuse-link contacts
should be measured at the end of each of the tests defined in clauses 13.3, 13.4 and 13.6 and the value
should not exceed 1 1 O of the initial value.
13.2.2 If any fuse-@ fails to pass the type tests a further group of fuse-links should be tested. If any of these
fail, the fuse-links should be deemed not to comply with the requirements of this IS0 Recommendation.
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13.2.3 Items used in tests in any one group should not
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