General

JERG-2-212

DESIGN STANDARD
WIRE DERATING

Sept 3, 2008

Japan Aerospace Exploration Agency

JERG-2-212

This is an English translation of JREG-2-212. Whenever there is anything ambiguous in thisdocument, the original document (the Japanese version) shall be used to clarify the intent of therequirement.

Disclaimer
The information contained herein is for general informational purposes only. JAXA makes nowarranty, express or implied, including as to the accuracy, usefulness or timeliness of any information
herein.
JAXA will not be liable for any losses relating to the use of the information.

Published by
Japan Aerospace Exploration Agency
Safety and Mission Assurance Department
2-1-1 Sengen Tsukuba-shi,Ibaraki 305-8505, Japan

JERG-2-212

Contents
1. Scope of Application ........................................................................................................................... 1
2. Related Documents ............................................................................................................................. 1
2.1 Applicable documents .................................................................................................................. 1
2.2 Reference Documents ................................................................................................................. 1
3. Definition of Terms and Abbreviations ............................................................................................... 2
3.1 Definition of Terms........................................................................................................................ 2
3.2 Abbreviations ................................................................................................................................ 2
4. General Requirements ........................................................................................................................ 2
5. Requirements ...................................................................................................................................... 3
5.1 Applicable Temperature ............................................................................................................... 3
5.2 Recommended Current ................................................................................................................ 3
5.2.1 Maximum Current for Single Line ........................................................................................ 3
5.2.2 Recommended Current for Bundled Lines ......................................................................... 3
5.2.3 Types of Power Lines ........................................................................................................... 4
5.2.4 Wire Numbers of Power Lines ............................................................................................. 4
5.2.5 Consideration of Case in which Different Wire Numbers are Mixed ................................ 4
5.3 Maximum Current giving Consideration to Duty ........................................................................ 7
5.4 Measures in the Event of Nonconformity to the Recommended Values ................................. 7
5.5 When Use at Even Lower Temperatures is Desired ................................................................. 7
6. Appendix

8

Appendix I Material Property Tests ......................................................................................................... 9
1. Applicable Temperatures ............................................................................................................. 9
2. Effects of Space Environment Factors ....................................................................................... 9
Appendix II Derating Acquisition Test ................................................................................................... 12
References ........................................................................................................................................ 19ⅰ

JERG-2-212

1.

Scope of Application
This standard provides the recommended current values for Raychem®55 wire, which is
widely used in spacecraft, including for the wiring within components.
Wires exposed to the external environment outside the spacecraft must be designed withconsideration given to the effects exerted by the space environment, such astemperature, radiation, atomic oxygen, and ultraviolet rays, and the recommended
allowable current values defined in this standard may not be appropriate. Therefore,
please note that, for wires exposed to the external space environment, detailed
consideration of operating conditions - such as the mission profile of the spacecraft – arerequired. Appendix I in Section 6 describes the effects of space environment factors thatshould be considered.

2.

Related Documents

2.1 Applicable documents
Within the scope defined herein, the following documents constitute part of thisstandard. If a conflict occurs between this standard and the applicable documents, thespecifications in this standard take precedence.
(1) MIL-STD-975
NASA Standard Electrical, Electronic, and Electromechanical (EEE) Parts List
(2) NASA/TP 2003 212242
EEE-INST-002: Instructions for EEE Parts Selection, Screening, Qualification,
and Derating
2.2 Reference Documents
The following are reference documents relating to this design standard:(1) ECSS-Q-60-11A
Space product assurance Derating and end-of-life parameter drifts - EEE
components(2) ASTM E595
Standard Test Method for Total Mass Loss and Collected Volatile Condensable
Materials from Outgassing in a Vacuum Environment

1

JERG-2-212

3.

Definition of Terms and Abbreviations

3.1 Definition of Terms(1) Single jacket wire
A wire insulated with one layer of insulation sheath.
(2) Twisted double jacket wire
A wire consisting of one layer of insulation sheath covering insulated twisted-pairwires that are further covered with one layer of insulation.

3.2 Abbreviations

4.

AWG

American Wire Gauge

ETFE

Ethylene TetraFluoroEthylene

MLI
SLI

Multi Layer Insulator
Single Layer Insulator

Standard for wires in the USA
Copolymerized ethylene tetrafluoride andethylene
Insulator consisting of multiple layers
Insulator consisting of a single layer

General Requirements
In general, the rated current of a wire is required in order that the wire be used at or
below its rated temperature, this temperature being determined by the insulation used.
The rated temperature for the Raychem®55 wire considered in this standard(silver-plated wire with electron beam crosslinked ETFE - i.e. copolymerized ethylene
tetrafluoride and ethylene - sheath material) is 200°C (the rated temperature for tinned
wire is 150°C). However, this represents only the guaranteed temperature for the unit
and, since there is a failure mode in which the sheath adheres at 200°C or lower, the wire
should be used at or below 150°C.
This standard defines the wire derating of the Raychem®55 wire under standard usage
conditions. When using other wire materials, and for usage beyond the conditions of thisstandard, the following must be considered individually for each project:(1) Performance of detailed thermal analysis on a wire harness (including bundledwires) using large currents and a study of the resulting effects.
(2) In the case of wires being bundled, specification of an appropriate current value fora single wire and for the relevant number of bundled wires, giving consideration toheat generation.

2

JERG-2-212

5.

Requirements

5.1 Applicable Temperature
The maximum temperature of the wire must not exceed 150°C.
However, the above need not be applied if, even though the maximum temperature
exceeds 150°C, it is proved that the wire sheath will not crack during the mission
period.
In addition, the effect of temperature on the connectors and components in the vicinityof the wire must be considered.

5.2 Recommended Current
5.2.1 Maximum Current for Single Line
This standard adopts the requirements of MIL-STD-975 APPENDIX A 3.16, which is
widely used to date, and the requirements of NASA Instruction EEE-INST-002
SECTION W1, use of which has begun recently (for single wire, the current values inboth standards are the same). Table 5.2-1 shows the recommended maximum
currents for a single wire. These values are for a thermal vacuum environment with anambient temperature of 70°C.

Table 5.2-1 Recommended maximum current for single line
Wire
diameter
AWG
Current
(A)

30

28

26

24

22

20

18

16

14

12

10

8

6

4

1.3

1.8

2.5

3.3

4.5

6.5

9.2

13

19

25

33

44

60

81

5.2.2 Recommended Current for Bundled Lines
Figures 5.2-1 and 5.2-2 show derating against maximum currents in a single line, with
the number of bundled power line wires (i.e. the number of power lines only in the caseof mixed power and signal lines) as the parameter. (For reference, the requirements ofthe conventionally adopted MIL-STD-975 are shown in the figure.) These diagramsmust be used to verified that the current in the power lines is appropriate with regard to
the configuration of the designed parts (ratio between power lines and signal lines,
insulation material), and operating temperatures. (The upper and lower graphs shownin Figures 5.2-1 and 5.2-2 show the same data using different scales. Either figure may
be used, according to convenience.) The points in the diagrams indicate the derating
found in the test. Although it is possible to read interpolation values on the basis of the3

JERG-2-212

graph, derating cannot be determined simply by linear extrapolation. Appropriate
assessment is necessary in the case of bundled lines requiring extrapolation.
With respect to electromagnetic interference, it is desirable to separate power lines
from signal lines. However, if this is not possible, the heating power lines should beconsidered as being at the center of the bundled lines for purposes of thermal design(practical implementation design) since this represents the worst situation. Figures
5.2-1 and 5.2-2 show derating under such conditions.

In the figures, power line +SLI and power line +MLI were tested in a configuration inwhich the power line was coated with insulation material. It must be noted that
although this configuration suppresses external heat radiation, it also requires thatlarge derating be considered.
The figures are based on assessment test data from the Japan Aerospace Exploration
Agency. Excerpts of the supporting data are shown in Appendix II in Section 6.

5.2.3 Types of Power Lines
Single jacket wire and twisted double jacket wire were used for assessment, thesebeing the types usually used in power lines, and it was verified that there were no
significant differences between them. Accordingly, single jacket or twisted double
jacket wire must be used when applying this standard. Additional assessment isrequired if other types of wire are used.

5.2.4 Wire Numbers of Power Lines
AWG20 wire was employed in testing, this being the most frequently used. However,the data presented here is also applicable to wires thinner than AWG14, in accordancewith MIL-STD-975 specifying no difference in derating depending on wire thickness,and ECSS-Q-60-11A specifying no difference between AWG14 and thinner wires(although it gives a different specification for AWG12 and thicker).

5.2.5 Consideration of Case in which Different Wire Numbers are Mixed
If different wire numbers are used together, derating should be determined with thetotal number of lines to be bundled into power lines regarded as the number of bundles,
and the allowable currents for each wire number should be found on the basis of the
maximum current in a single line (Table 5.2-1).

4

JERG-2-212

Derating

Ambient temperature 40°C

Number of power lines only (signal lines not included)
Power lines
Power lines and signal lines (ratio of numbers: 3:7)
Power lines and MLI

Power lines and signal lines (ratio of
numbers: 1:9)
Power lines and SLI
MIL-975

Derating

Ambient temperature 40°C

Power lines
Power lines and signal lines (ratio of numbers: 3:7)

Power lines and signal lines (ratio of
numbers: 1:9)
Power lines and SLIPower lines and MLI

Figure 5.2-1 Derating of maximum current in single line with number of wire bundles asparameter (ambient temperature: 40°C)
Note: To find the maximum current value for a bundled line, use the value of maximum
current for a single line shown in Section 5.2.1.

5

JERG-2-212

Derating

Ambient temperature @ 60°C

Number of power lines only (signal lines not included)
Power lines
Power lines and signal lines (ratio of
numbers: 3:7)

Power lines and signal lines (ratio of
numbers: 1:9)
MIL-975

Derating

Ambient temperature 60°C

Number of power lines only (signal lines not included)
Power lines

Power lines and signal lines (ratio of
numbers: 1:9)

Power lines and signal lines (ratio of
numbers: 3:7)

Figure 5.2-2 Derating of maximum current in single line with number of wire bundles asparameter (ambient temperature: 60°C)
Note: To find the maximum current value for a bundled line, use the value of maximum
current for a single line shown in Section 5.2.1.

6

JERG-2-212

5.3 Maximum Current giving Consideration to Duty
In consideration of duty, if the peak current to be employed exceeds the maximum
current given in Section 5.2, it must be proved by test or analysis that the requirements
given in Section 5.1 are satisfied at the peak current wire temperature.
The maximum current in Section 5.2 is specified for constant current flow. For a pulse
operated device, it is possible to control temperatures to below the specified level eventhough the maximum connected current is higher than the value shown in the previous
section. However, it must be noted that, depending on the thermal capacity of the wire
acting as heating element and on the duty factor, the temperature indicated in theprevious section may be exceeded even at a low current levels. (For example, if thethermal capacity is low and there is a long continuous energizing period, a peak current
flow twice the level shown in the previous section would not be acceptable at a duty of25%.)

5.4 Measures in the Event of Nonconformity to the Recommended Values
The recommended values indicated in this standard are not necessarily applicable toall types of implementation. They have, with a view to generalization, been determinedon the basis of assessment test results conducted under conditions in which the endsof the line material were thermally insulated. Hence, the validity of designing inaccordance with the current values in this standard should be checked and, in cases of
non-conformity, it must be proved that the relevant harness designs present no thermal
problems by setting up thermal models of the corresponding parts.

5.5 When Use at Even Lower Temperatures is Desired
The recommended values indicated in this standard specify derating which satisfies theapplicable temperatures given in Section 5.1. For use at even lower temperatures, refer
to Section 6 Appendix II.

7

JERG-2-212

6.

Appendix
In order to prepare this design standard, various tests were conducted on Raychem®55
wire. The main information obtained from these tests is given in this Appendix.

8

JERG-2-212

Appendix I
1.

Material Property Tests

Applicable Temperatures
The recommended values specified in this standard are based on the results ofassessment tests conducted on Raychem®55 wire for use in space (this product has along record of proven performance in space). Raychem®55 is an electron beamcrosslinked ETFE wire. Although it has rated temperature of 200°C (the temperature atwhich it maintains an elongation of 50% under a temperature load of 10,000 hours),
this is not a guaranteed value when implementation conditions and thermal cycles are
considered. The following gives information obtained from the results of assessment
tests which assume standard use in spacecraft. If lines of the same material arebundled and reach a temperature exceeding 160°C due to heat generation, thesheaths adhere to each other and the lines form a cluster even after unbundling.
•

If lines of the same material are bundled and left in conditions under which line

temperature reaches 150°C due to heat generation, unbundling causes the lines toseparate from each other, although slight adherence exists between sheathes.
•

According to the results of TG/DTA analysis on the sheath, a minute change inphysical properties is detected at around 100°C.
•

The crystalline melting point is approximately 236°C. Hence, the rated temperatureof 200°C is assumed to have been specified in consideration of the crystalline melting
point.
•

Testing of the sheath material conducted using DMA (Dynamic MechanicalAnalysis) showed slight expansion in the circumferential direction when temperature
exceeded a point around 160°C, and sudden shrinkage (with rising temperature) was
observed at around the crystalline melting point. In contrast, in the longitudinal direction
the sheath material suddenly expanded at around the crystalline melting point. In theheating cycle up to 150°C, slight expansion caused by heating was observed,
representing deformation within the scope of elasticity of the sheath material andleading to only a low mechanical load. The rated temperature of general ETFE
(non-crosslinked) is 150°C. This value was therefore specified as the recommended
temperature. 1)

2.

Effects of Space Environment Factors
Raychem®55 wire sheath material for use in space is subject to the effects exerted by
space environments, such as degradation of thermo-optic properties due to ultraviolet

9

JERG-2-212

rays (increasing absorptance of sunlight), decrease in elongation due to electron
beams, and corrosion by atomic oxygen - as shown below. In addition, themultiplicative effects that occur in these complex environments are not well understood.
Shielding with thermal control materials is recommended to avoid direct exposure to
the space environment.

(1) Ultraviolet rays
Ultraviolet rays have an effect on the material that reaches as far as the rays penetrate.
(This depends on absorption of the ultraviolet rays by the material.) In addition to direct
reaction to irradiation with ultraviolet rays, active substances created by the rays canaffect the surroundings.
Raychem®55 wire sheath material for use in space shows a clear increase in sunlightabsorptance resulting from irradiation with ultraviolet rays. The effect becomespronounced as the temperature of the specimen rises. No change in infrared ray
emissivity is observed.
In order to make an assessment of their effect on mechanical properties, ultraviolet
rays were introduced up to 100ESD at room temperature. No decrease in theelongation of the sample was seen after irradiation with ultraviolet rays only ascompared with a test sample before irradiation. When an environmental load ofelectron beams, heating, and ultraviolet rays - in that order - was applied, greater
elongation occurred than when only electron beams then heating were applied.
Degradation due to ultraviolet rays is concentrated on surfaces. Other parts, where thedegradation is less significant, are dominant in the determination of mechanicalproperties, and this is believed to be the reason that no changes appeared.

(2) Electron beam
Raychem®55 wire sheath material for use in space has improved mechanicalproperties as a result of cross-linking by an electron beam. However, as the absorbed
dose increases, not only cross-linking but also the ratio of cut chains increases, andthis leads to degradation in mechanical strength.
NASA’s cable selection guide describes it as “More resistant to radiation effects” (to 5 x
107 RADS  500 kGy).
JAXA conducted tests using irradiation with an electron beam of 25 to 200kGy followedby exposure to a 190°C thermal vacuum for 7 days, and observed changes in
elongation. The 150% elongation of a test sample before irradiation changed toapproximately 60% after irradiation at 200kGy. This value does not necessarily indicate

10

JERG-2-212

that elongation will cause an immediate break. However, it is desirable to use sheathmaterials within their scope of elasticity in consideration of expansion and shrinkage
during thermal cycles.
The surface of the sheath material showed clear browning after irradiation by anelectron beam of 1430kGy at a specimen temperature of 230°C. However, lower
irradiation at room temperature showed only slight discoloration.

(3) Atomic oxygen
Irradiation testing with atomic oxygen showed a reaction efficiency of 1.710-24(cm3/atom, the volume lost per oxygen atom). This value is closer to those forpolyimide (1.5~3.0 10-24) and polyethylene (3.3~3.7 10-24) than those for many
fluororesins, which are 0.110-24 or lower. Hence, the kind of resistance against
atomic oxygen that is exhibited by fluororesins cannot be expected.
If the material is to be exposed to a low-orbit environment with a high volume of atomic
oxygen, the decrease in material thickness (which affects both electric and mechanicalproperties) resulting from atomic oxygen must be taken into consideration.

(4) Outgassing
ASTM E595 outgassing property measurement results are as follows:
Total Mass Loss (TML): 0.098%
Collected Volatile Condensable Materials (CVCM): 0.002%
Water Vapor Regained (WVR): 0.025%
The data shows the properties of materials for use in space.

11

JERG-2-212

Appendix II Derating Acquisition Test
Appendix II shows excerpts of data from tests conducted in order to determine derating.
The derating shown in Section 5.2.2 is specified based on this test data, and on thecurrent value at which the central temperature reaches 120°C. 120°C was specified on
the grounds of test error (maximum 20°C) and unpredictable errors (maximum 10°C)
resulting from actual harness installation.
Figures II-1 to 4 show the results of the Derating Acquisition Test, and Table II-1
summarizes the test conditions.
In addition, Figure II-5 shows a comparison of the results obtained through the derating
acquisition tests by difference in ambient temperature, and Figure II-6 shows acomparison by difference in signal line ratio.

Table II-1 Derating Acquisition Test Conditions
Ambient
FigureSpecimentemperature
FigureBundle of power lines only
40°C
II-1
FigureBundle of power lines only
60°C
II-2
FigureMixed bundle of power lines
40°C
II-3
and signal lines
FigureMixed bundle of power lines
60°C
II-4
and signal lines

12

JERG-2-212

50 power lines(AWG20) @40°C
Temperature at center(°C)

Temperature at center(°C)

100 power lines(AWG20) @40°C

Current(A)Current(A)150 power lines(AWG20) @40°C
Temperature at center(°C)

Temperature at center(°C)

300 power lines(AWG20) @40°C

Current(A)Current(A)Figure II-1 Results of derating acquisition test conducted on bundled power lines only at an ambient temperature of 40°C

13

JERG-2-212

50 power lines(AWG20) @60°C
Temperature at center(°C)

Temperature at center(°C)

100 power lines(AWG20) @60°C

Current(A)Current(A)150 power lines(AWG20) @60°C
Temperature at center(°C)

Temperature at center(°C)

300 power lines(AWG20) @60°C

Current(A)Current(A)Figure II-2 Results of derating acquisition test conducted on bundled power lines only at an ambient temperature of 60°C

14

50 power lines (AWG20) and 450 signal lines (AWG30) @40°C

100 power lines (AWG20) and 900 signal lines (AWG30) @40°C

Temperature at center(°C)

Temperature at center(°C)

JERG-2-212

Current(A)150 power lines (AWG20) and 350 signal lines (AWG30) @40°C

300 power lines (AWG20) and 700 signal lines (AWG30) @40°C

Temperature at center(°C)

Temperature at center(°C)

Current(A)Current(A)Current(A)Figure II-3 Results of derating acquisition test conducted on mixed bundles of power and signal lines at an ambient temperature of 40°C

15

50 power lines (AWG20) and 450 signal lines (AWG30) @60°C

100 power lines (AWG20) and 900 signal lines (AWG30) @60°C

Temperature at center(°C)

Temperature at center(°C)

JERG-2-212

Current(A)150 power lines (AWG20) and 350 signal lines (AWG30) @60°C

300 power lines (AWG20) and 700 signal lines (AWG30) @60°C

Temperature at center(°C)

Temperature at center(°C)

Current(A)Current(A)Current(A)Figure II-4 Results of derating acquisition test on mixed bundles of power and signal lines at an ambient temperature of 60°C

16

Derating

JERG-2-212

Number of lines
Power line@60°C

MIL-975

Derating

Power line@40°C

Number of lines
Power line@40°C

Power line@60°C

Figure II-5 Comparison by difference in ambient temperature

17

JERG-2-212

Ambient
temperature40°C

Derating

Derating

Ambient
temperature40°C

Total number of lines

Ratio of power lines
Total number oflines 500

Total number oflines 1000

Ratio of power lines 0.1

Ratio of power lines 0.3

Ambient
temperature 60°C

Derating

Derating

Ambient
temperature 60°C

Total number of lines

Ratio of power lines
Total number oflines 500

Total number oflines 1000

Ratio of power lines 0.1

Figure II-6 Comparison by signal line ratio

18

Ratio of power lines 0.3

JERG-2-212

References
1) Jun-ichiro Ishizawa, et. al.: ADEOS-II Harness Thermal Cycle Verification,
Spacecraft Environment Symposium (2005)

19