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IS0
INTER NAT1 O NAL O RGANl ZATl O N FOR STAN DARD IZATl O N
I SO RECOM M EN DATI ON
R 474
PERFORMANCE REQUIREMENTS
FOR GENERAL PURPOSE ELECTRICAL CABLES
WITH COPPER CONDUCTORS FOR AIRCRAFT
1st EDITION
February 1966
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and ISO- 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 474, Performance Requirements for General Purpose Electrical
Cables Mtitfi Copper Conductors for Aircraft, was drawn up by Technical Committee ISO/TC 20,
Aircraft, the Secretariat of which is held by the British Standards Institution (BSI).
Work on this question by the Technical Committee began in 1958 and led, in 1960, to
the adoption of a Draft IS0 Recommendation.
In March 1961, this Draft IS0 Recommendation (No. 421) was circulated to all the IS0
Member Bodies for enquiry. It was approved by the following Member Bodies:
Australia France Portugal
Belgium Germany Spain
Canada Iran Sweden
Chile Israel United Kingdom
Colombia Italy U.S.S.R.
Czechoslovakia Netherlands Yugoslavia
Finland New Zealand
No Member Body opposed the approval of the Draft.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in February 1966, to accept it as an IS0 RECOMMENDATION.
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IÇOIR 414 - 1966 (E)
IS0 Recommendation R 474 February 1966
PERFORMANCE REQUIREMENTS
FOR GENERAL PURPOSE ELECTRICAL CABLES
WITH COPPER CONDUCTORS FOR AIRCRAFT
1. SCOPE
1.1 This IS0 Recommendation states the requirements for cables for general purpose wiring
of aircraft circuits in which the voltage between conductors, or between a conductor and
metal braid or the aircraft structure, does not exceed 600 volts (r.m.s.) and in which the
frequency does not exceed 1600 Hz. The cables are suitable for use where, in continuous
service, no combination of ambient temperature and conductor current produces a stabilized
conductor temperature in excess of 105 OC. These cables are suitable for fixed wiring in
aircraft at a temperature down to - 75 OC, but are not suitable for severe flexing at temper-
atures below - 30 OC. These cables do not support combustion, but they should not be
regarded as complying with the requirements of IS0 Recommendation R . . . * in regard
to fire resistance.
1.2 This IS0 Recommendation includes the requirements for cables with copper conductors
or composite conductors, including those with an outer covering in the form of a metal braid.
2. TERMINOLOGY
2.1 Conductor. Conducting portion of a cable.
2.2 Wire. Cylindrical metallic wire of uniform cross-sectional area, used to form the conductor.
2.3 Stranded conductor. Conductor composed of a number of wires twisted together. When the
conductor consists of more than one layer, alternate layers are twisted in opposite directions.
2.4 Bunched conductor. Conductor composed of a number of wires in which all wires are twisted
together in the same direction.
2.5 Rope lay conductor. Conductor in which a number of groups of wires are assembled in
concentric layers. Each group may consist of wires assembled in stranded or bunched
formation.
2.6 Composite conductor. Conductor composed of copper wires and/or wires of a metal of greater
strength.
2.7 Insulation. Part of a cable which serves to insulate the conductor.
2.8 Core. Conductor and insulation of a cable, excluding all additional coverings.
Part 5: Fire
* IS0 Recommendation R . . ., Environmental and operational conditions of' aircraft electrical equipment.
resistance, at present Draft IS0 Recommendation No. 766.
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ISOIR 474 - 1966 (E)
2.9 Protective covering. Outside covering of a cable, protecting the insulation against deterioia-
tion caused by abrasion or injurious fluids.
2.10 Meral braid. A number of wires applied spirally over the insulation or protective covering
and interwoven to form a uniform and substantially continuous covering.
2.11 Cable. Complete assembly of conductor, insulation and protective covering.
2.12 Sarnple. Amount of cable of one and the same dimension and type, taken from a batch.
2.13 Test piece. Continuous length of cable taken from a sample.
3. MATERIALS
3.1 Copper wires should be of annealed high conductivity copper ,,aving a resistivity not greater
than the value fixed by the International Electrotechnical Commission (I E C) for " Standard
annealed copper".* Each wire should be uniformly coated with pure tin.
3.2 The tensile strength and elongation of wiles taken from conductors should conform to the
appropriate values shown in Table 1, which are based on a gauge length of 10 in (254 mm)
held in clamps separated at a rate not exceeding 12 in (300 mm) per minute, the tensile
strength being calculated on the original cross-sectional area of the wire.
TABLE 1. - Tensile tests on wires
Minimum
Diameter Tensile strength
Material
elongation
I I
i 0.508 to 0.305 43 O00 max. ' 3023 max. 13.5
0.020 to 0.012
i
Copper
0.01 1 to 0.003 1 0.279 to 0.076 44 O00 max. ~ 3094 max. 9.0
3.3 The conductors of Size 20 and Size 22 cables may be composed of copper wires and of wires
of a stronger metal with an equivalent conductivity and a tensile strength as given in Table 2,
below.
Minimum equivalent conductivity Minimum tensile
Cable size
in reference to copper strength
22 50 per cent 31 lbf (14 kgf)
44 lbf (20 kgf)
20 66 per cent
* I E C Publication No. 28, International Standard of Resistance .for Copper.
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IÇO/R 474 - 1966 (E)
3.4 Primary insulation and protective covering. The materials uscd for the primary insulation and
protective covering of the cables should be such that the finished cable will comply with all the
requirements of this IS0 Recommendation. The materials should be free from ingredients
likely to cause staining or diçcolouration of the cable.
4. CONSTRUCTION
4.1 Conductor
Conductors should consist of a number of wires, bunched, stranded, or in rope lay formation.
The wires should be tinned annealed copper complying with the relevant requirements of
section 3. Alternatively, and subject to the agreement of the airworthiness authority, the
conductor may consist of a mixture of tinned annealed copper wires and wires of a stronger
metal.
The complete conductor should not be joined. Individual wires may be joined, preferably by
brazing or soldering. Alternatively, in the case of wires of a diameter less than 0.012 in
(0.3 mm) the joint may be made by twisting the ends together. Not more than one joint
should occur in each 50 m of wire.
4.2 Complete cable
4.2.1 The insulation should be of uniform circular cross section throughout the length of the
cable and the conductor should be evenly centred in the insulation.
4.2.2 The insulation should not be loose, but it should be possible to strip th
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