NASA-STD-4003A.pdf

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METRIC/SI

NASA TECHNICAL STANDARD

NASA-STD-4003A

w/CHANGE 1:

REVALIDATED w/

ADMINISTRATIVE/

EDITORIAL CHANGES

2016-01-19

National Aeronautics and Space Administration

Approved: 2013-02-05

Superseding NASA-STD-4003

(Baseline)

ELECTRICAL BONDING FOR

NASA LAUNCH VEHICLES, SPACECRAFT,

PAYLOADS, AND FLIGHT EQUIPMENT

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NASA-STD-4003A w/CHANGE 1

DOCUMENT HISTORY LOG

Status Document

Revision

Change

Number

Approval Date Description

Baseline 2003-09-08 Initial Release

A

2013-02-05

Reformatted document to meet current

NASA Standard Template

Deleted the following document references:

MIL-C-5541, MIL-STD-889, NSTS 37330,

SAE-AMS-M-3171, SAE-ARP-1481

SAE-ARP-ILO1870, SSP 30245

Added the following Applicable

Documents:

NASA-STD-6012, NASA-STD-6016,

SAE-ARP-5414

Section 3.1: Added “CFRP carbon fiber reinforced plastic”

Section 3.1: Added “EMI

Electromagnetic Interference”

Section 3.1: Added “EUT Equipment under test”

Section 3.1: Changed GFRP acronym.

From: graphite filament reinforced plastic

To: glass or graphite fiber reinforced plastic

Section 3.2: In Electrical Bonding definition changed

From: “…mechanical interfaces…”

To: “…faying surface mechanical interfaces..”

Section 3.2: Deleted redundant word

“Provides” in third and forth bullet.

Section 3.2: Added “faying surface” definition

Table 1: Purpose of Class C Bond

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Revision

Change

Number

Approval Date Description

(Continued)

From: “Reduces power and voltage losses.”

To: “Reduces power and voltage losses at the bonding interfaces.”

Table 1:

Column: CLASS L, Row: BOND REQT.

From: “Bonding components shall withstand high current.”

To: “Bonding components are required to withstand high current without arcing.”

Section 4.1.2.2

From: “…ignition point…”

To: “…ignition temperature…”

Added section: 4.1.2.4 Pipe, Tubing, and

Hoses

Section 4.1.3.d:

From: “…ignition point…”

To: “…ignition temperature…”

Section 4.1.3.1

From: “…due to heating or arcing.”

To: “due to conditions including heating, sparking, or arcing.”

Figure 1: Changed curve title.

From: “Maximum Resistance”

To: “Maximum Allowable Resistance”

Section 4.1.4.1: Changed paragraph title.

From: “Electrical Connectors”

To: “Electrical Connectors and Shield

Termination”

Section 4.1.5.a: Rearranged sentence to add clarity.

Section 4.1.6: Converted inches to centimeters

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Revision

Change

Number

Section 4.1.6.b (1): Added requirement for conductive coatings.

Section 4.1.6.b (2): Added information for surface conductivity.

Section 4.1.6.2

From: “…20 decibels (dB) less than applicable minimum ignition energy (MIE) threshold level…”

To: “1/10 of applicable minimum ignition energy (MIE) (or 20 decibels (dB) below) threshold level…”

Section 5.1.2: Moved the information from the following sections to 5.1.2 Bond Straps:

4.3.3 Bond Straps

4.4.2 Conductivity of Bond Joint

4.4.3 Bond Straps

Added section “5.1.3 Fasteners”

Removed detailed information on surface cleaning and finishing and pointed to

NASA-STD-6012 and NASA-STD-6016 instead.

Deleted the following sections:

5.2.1 Aluminum

5.2.2 Magnesium

5.2.3 Steel

Deleted Table II, Galvanic Series.

Deleted Section 5.4, Special

Considerations, and changed to: 5.4

Graphite Filament Reinforced Plastic

(GFRP).

Section 5.4: Replaced “Graphite Filament

Reinforced Plastic (GFRP)” with “Carbon

Fiber Reinforced Plastic (CFRP).”

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Revision

Change

Number

Deleted Section 5.4.3 Multilayer

Insulation

Section 5.5.b: Added verbiage for end-to-end measurement option.

Section 5.5.f: Added verification for conductive coatings.

Section 5.5.g: Added verification for surface conductivity.

Deleted Section 6.7 Surface Cleaning and

Finishing

Moved Section 6.9 Special Considerations to the appendix and divided into the following sections:

A.3.8 Pipe, Tubing and Hoses (Class S)

A.3.9 Composite Materials

A.3.10 Multilayer Insulation

Section A.2: Added the following reference documents:

NASA-HDBK-4002

NASA-HDBK-4006

NASA-STD-4005

NASA-STD-464C

Section A.3.3

From: “…GFPR…”

To: “…glass or graphite fiber reinforced plastic (GFRP)…”

Section A.3.6: Added information on triboelectrification.

Section A.3.11: Added information on verification processes.

Section A.3.11: Added information on clamping pressure.

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Revision

Change

Number

2013-02-05 Section A.3.11: Added Figure 2, Electrical

Bonding Path Diagram Example

2016-01-19 Revalidated w/Administrative/Editorial

Changes—This NASA Technical Standard was reviewed and no technical changes resulted. However, requirements EBR 33, 34, 43, 92, and 93 were clarified based on information contained in related notes; and requirement 5.2.f was re-lettered to 5.2.e.

Administrative changes to number requirements, add a Requirements

Compliance Matrix as Appendix A, and conform to the current template were made, along with editorial corrections.

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FOREWORD

This NASA Technical Standard is published by the National Aeronautics and Space

Administration (NASA) to provide uniform engineering and technical requirements for processes, procedures, practices, and methods that have been endorsed as standard for NASA programs and projects, including requirements for selection, application, and design criteria of an item.

This NASA Technical Standard is approved for use by NASA Headquarters and NASA Centers and

Facilities and may be cited in contract, program, and other Agency documents as a technical requirement. It may also apply to the Jet Propulsion Laboratory and other contractors only to the extent specified or referenced in applicable contracts.

This NASA Technical Standard establishes a common framework for consistent electrical bonding practices across NASA programs. The intent is to provide stand-alone requirements and to provide enough data to help modify requirements or to allow waivers if needed.

Requests for information should be submitted via “Feedback” at https://standards.nasa.gov. Requests for changes to this NASA Technical Standard should be submitted via MSFC Form 4657, Change

Request for a NASA Engineering Standard.

Original Signed By _ ___________02/05/2013_____________

Ralph R. Roe, Jr. Approval Date

NASA Chief Engineer

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SECTION

TABLE OF CONTENTS

PAGE

DOCUMENT HISTORY LOG

FOREWORD

TABLE OF CONTENTS

LIST OF APPENDICES

LIST OF FIGURES

LIST OF TABLES

1. SCOPE

1.1 Purpose

1.2 Applicability

1.3 Tailoring

2. APPLICABLE DOCUMENTS

2.1 General

2.2 Government Documents

2.3 Non-Government Documents

2.4 Order of Precedence

3. ACRONYMS AND DEFINITIONS

3.1 Acronyms and Abbreviations

3.2 Definitions

4. GENERAL REQUIREMENTS

4.1 Electrical Bonding

4.1.1 Assembly Drawings

4.1.2 Power Current Return Path (Class C)

4.1.2.1 Bond Joints

4.1.2.2 Magnesium Alloy

4.1.2.3 Hazardous Area Bonding

4.1.2.4 Piping, Tubing, and Hoses

4.1.3 Shock and Fault Protection (Class H)

4.1.3.1 Hazardous Area Bonding

4.1.4 Electromagnetic Interference or Radio Frequency (Class R)

4.1.4.1 Electrical Connectors and Shield Termination

4.1.4.2 Antennas

4.1.5 Lightning Protection (Class L)

4.1.5.1 Hazardous Area Bonding

4.1.6 Electrostatic Discharge (Class S)

4.1.6.1 Multilayer Insulation

4.1.6.2 Hazardous Area Bonding

4.1.6.3 Pipe, Tubing, and Hoses

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SECTION

TABLE OF CONTENTS (Continued)

5. DETAILED REQUIREMENTS

5.1 Bonding Methods

5.1.1 Metal-to-Metal (faying surface to faying surface)

5.1.2 Bond Straps

5.1.3 Fasteners

5.2 Surface Cleaning and Finishing

5.3 Galvanic Corrosion of Dissimilar Materials

5.4 Carbon Fiber Reinforced Plastic

5.5 Verification

LIST OF APPENDICES

APPENDIX PAGE

A Requirements Compliance Matrix

B Guidance

B.1 Purpose

B.2 Reference Documents

B.3 Guidelines

B.3.1 Design Parameters

B.3.2 Power Current Return Path (Class C)

B.3.3 Shock and Fault Protection (Class H)

B.3.4 Electromagnetic Interference or Radio Frequency (Class R)

B.3.5 Lightning Protection (Class L)

B.3.6 Electrostatic Discharge (Class S)

B.3.7 Galvanic Corrosion of Dissimilar Materials

B.3.8 Pipe, Tubing and Hoses (Class S)

B.3.9 Composite Materials

B.3.10 Multilayer Insulation

B.3.11 Verification

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FIGURE

LIST OF FIGURES

1 Fault Current vs. Maximum Bonding Resistance in the Presence of

Flammable Vapors or Liquids

2 Electrical Bonding Diagram-Example

TABLE

LIST OF TABLES

1 Summary of Electrical Bonding Classes

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ELECTRICAL BONDING FOR NASA LAUNCH VEHICLES,

SPACECRAFT, PAYLOADS, AND FLIGHT EQUIPMENT

1. SCOPE

1.1 Purpose

The purpose of this NASA Technical Standard is to define the basic electrical bonding requirements for NASA launch vehicles, spacecraft, payloads, and equipment. Its intent is to provide fundamental aerospace electrical bonding requirements, as well as to classify electrical bonds according to their purpose. This NASA Technical Standard also states the requirements for the various classes. The rationale for specific requirements is stated where possible.

Additional data is provided to support tailoring for new applications, if necessary.

1.2 Applicability

This NASA Technical Standard is applicable to engineering practices for NASA programs and projects.

This NASA Technical Standard is approved for use by NASA Headquarters and NASA Centers and

Facilities and may be cited in contract, program, and other Agency documents as a technical requirement. It may also apply to the Jet Propulsion Laboratory and other contractors only to the extent specified or referenced in applicable contracts.

Verifiable requirement statements are numbered and indicated by the word “shall”; this NASA

Technical Standard contains 97 requirements. Explanatory or guidance text is indicated in italics beginning in section 4. To facilitate requirements selection and verification by NASA programs and projects, a Requirements Compliance Matrix is provided in Appendix A.

1.3 Tailoring

[EBR 1] Tailoring of this NASA Technical Standard for application to a specific program or project shall be formally documented as part of program or project requirements and approved by the responsible Technical Authority in accordance with NPR 7120.5, NASA Space Flight Program and

Project Management Requirements.

2. APPLICABLE DOCUMENTS

2.1 General

The documents listed in this section contain provisions that constitute requirements of this NASA

Technical Standard as cited in the text.

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2.1.1 [EBR 2] The latest issuances of cited documents shall apply unless specific versions are designated.

2.1.2 [EBR 3] Non-use of specifically designated versions shall be approved by the responsible

Technical Authority.

The applicable documents are accessible at https://standards.nasa.gov, may be obtained directly from the Standards Developing Body or other document distributors, or information for obtaining the document is provided.

2.2 Government Documents

National Aeronautics and Space Administration

NPR 7120.5 NASA Space Flight Program and Project Management

Requirements

NASA-STD-6012 Corrosion Protection for Space Flight Hardware

NASA-STD-6016 Standard Materials and Processes Requirements for Spacecraft

2.3 Non-Government Documents

Society of Automotive Engineers (SAE) Aerospace

SAE-ARP-5412 Aircraft Lightning Environment and Related Test Waveforms

SAE-ARP-5414 Aircraft Lightning Zoning

2.4 Order of Precedence

2.4.1 The requirements and standard practices established in this NASA Technical Standard do not supersede or waive existing requirements and standard practices found in other Agency documentation.

2.4.2 [EBR 4] Conflicts between this NASA Technical Standard and other requirements documents shall be resolved by the responsible Technical Authority.

3. ACRONYMS AND DEFINITIONS

3.1 Acronyms and Abbreviations

mH Microhenries ac alternating current

AWG American Wire Gauge

CFRP carbon fiber reinforced plastic

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CLASS C class of bond for intentional current return

CLASS H class of bond for fault current return

CLASS L class of bond for lightning current

CLASS R class of bond for radio frequency current

CLASS S class of bond for dissipation of electrostatic charge cm Centimeter dB Decibels dc direct current

EBR Electrical Bonding Requirements

EED electro-explosive device

EMF electromotive force

EMI electromagnetic interference

ESD electrostatic discharge

ETR Eastern Test Range

EUT equipment under test ft foot/feet freq frequency

GFRP glass or graphite fiber reinforced plastic

MHz megahertz

MIE minimum ignition energy

NASA National Aeronautics and Space Administration

RF radio frequency rqmt requirement

SAE Society of Automotive Engineers sec second/seconds

STD standard (as in document)

3.2 Definitions

Electrical Bonding: The process of providing good electrical connection across faying surface mechanical interfaces to minimize electrical potential differences between equipment and individual parts of structure. Good electrical bonding provides the following:

• Fault current paths for protection against fire and personnel shock.

• A low impedance bond path for antenna installations to ensure no degradation of acceptable performance and to protect the antenna element from damage caused by P-static, radio frequency (RF) currents, or lightning events.

• A current path for RFs for proper operation of filters and shields.

• Protection against the effects of lightning.

• A means to prevent or safely discharge static charges.

Electrical bonds are classified according to the purpose for the bond. Table 1, Summary of

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Electrical Bonding Classes, gives a summary of the classes of bonds.

Faying Surface: The surface of metal materials in contact with each other and joined together.

Flight Vehicle: The launch vehicle and spacecraft or payload (if the payload outer surfaces are exposed to the triboelectrification process), and fairings or shrouds protecting payloads.

P-static: The precipitation static due to impact of charged particles on antennas.

Q: The ratio of reactance to resistance in a tuned circuit.

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Table 1—Summary of Electrical Bonding Classes

4. GENERAL REQUIREMENTS

This section describes the various classes of electrical bonding. Each section contains the general requirement, specific design requirements, and, in most cases, measurable resistance values for each class of bond. Guidelines in Appendix B discuss the reasons for some of the requirements and provide data for possible modifications or rationale for waivers to the requirements.

POWER RETURN SHOCK HAZARD

RADIO

FREQUENCY

LIGHTNING

ELECTROSTATIC

CHARGE

BOND CLASS CLASS C CLASS H CLASS R CLASS L CLASS S

PURPOSE OF

BOND

Reduces power and voltage losses at the bonding interfaces.

Applies to equipment and structure, which are required to return intentional current through structure.

Protects against fire or shock to personnel.

Applies to equipment and structure that may be required to carry fault current in case of a short to case or structure.

Protects equipment from RF emissions.

Applies to equipment that could generate, retransmit, or be susceptible to RF.

Includes antenna mounts and cable shield connections.

Covers wide frequency range.

Protects equipment from lightning effects.

Applies to equipment or structure that would carry current resulting from a lightning strike.

Protects against electrostatic discharge. Applies to any item subject to electrostatic charging.

BOND

REQMT.

Requires low impedance and low voltage across joints to assure adequate power to the user.

Jumpers and straps acceptable.

Requires low impedance and low voltage across joints to prevent shock hazard or fire due to short. Jumpers and straps acceptable.

Requires low RF impedance at high frequency. Direct contact preferred. No jumpers. Short, wide strap may be used as last resort.

Requires low impedance at moderate frequency.

Bonding components are required to withstand high current without arcing. Straps and jumpers are required to withstand high magnetic forces.

Allows moderate impedance. Jumpers and straps acceptable.

DC BOND

RESISTANCE

REQMT.

Bonding resistance requirement depends on current.

Bonding resistance requirement, 0.1 ohm or less. Special requirements when near flammable vapors.

Bonding resistance requirement, 2.5 milliohms or less.

Low inductance required.

Bonding resistance requirement depends on current. 500 volts or less across any joint. Low inductance required.

Typical bonding resistance requirement, 1.0 ohm or less.

FREQ.

REQMT.

Low Low High High Low

CURRENT

REQMT.

High High Low High Low

Low frequency bonds allow use of straps and jumpers.

High frequency bonds require low inductance paths. Short straps are sometimes acceptable.

High current bonds require large cross-sectional areas.

Low current bonds allow use of small contact areas.

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4.1 Electrical Bonding

[EBR 5] There may be more than one purpose for bonding a specific interface, and the bond shall meet the requirements of each applicable class.

4.1.1 Assembly Drawings

[EBR 6] Notes shall be provided on assembly drawings indicating the applicable class or classes.

4.1.2 Power Current Return Path (Class C)

[EBR 7] All circuits and systems that use vehicle structure for a power return path shall satisfy

Class C bonding requirements.

4.1.2.1 Bond Joints

a. [EBR 8] The total voltage drop across all electrical bond joints between the power supply and the load shall be controlled to keep the voltage within the tolerance of the applicable power quality standard.

b. [EBR 9] If no power quality standard is applicable, a default voltage drop value of 3.5 percent of the operating bus voltage shall be used.

Refer to Appendix B.3.2 for more information and joint resistance calculation.

4.1.2.2 Magnesium Alloy

[EBR 10] Magnesium alloy structure shall not be used as an intentional current return path.

The temperature of a poor joint could rise to the ignition temperature of magnesium.

4.1.2.3 Hazardous Area Bonding

a. [EBR 11] Electrical bonding of equipment or vehicle structure in areas where flammable materials, gases, or vapors may be present shall be adequate to prevent ignition due to heating, sparking, or arcing.

b. [EBR 12] The resistance of bond joints in hazardous areas shall not exceed the

Maximum Allowable Resistance curve shown in figure 1, Fault Current vs. Maximum Allowed

Bonding Resistance in the Presence of Flammable Vapors or Liquids.

If at all possible, the current return path should be routed around the hazardous area.

4.1.2.4 Pipe, Tubing, and Hoses

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[EBR 13] Pipes, tubing, and hoses shall not be used as an intentional return path for electrical current.

4.1.3 Shock and Fault Protection (Class H)

Fault current, due to short circuits to equipment case or structure, may cause shock or fire hazards. Refer to Appendix B.3.3 for more information.

a. [EBR 14] Exposed cases or chassis of electrical or electronic equipment shall be bonded to structure with a resistance of 0.1 ohm or less using the methods described in section

5.1.

b. [EBR 15] Metallic conduit, cable trays, and other conductive objects susceptible to short circuits shall have a resistance to structure of 0.1 ohm or less.

c. [EBR 16] For personnel and fire safety, the fault current return path shall be capable of conducting a minimum of 500 percent overload current for a time period of 0.5 second.

Typical personnel protection breakers will trip within 0.2 second after a hard short to case.

Resultant voltage on the enclosure of the affected component should not exceed 4.5 volts, and no fire or damage to the bond is allowed.

d. [EBR 17] Magnesium alloy structure shall not be used as a primary fault current return path.

The temperature of a poor joint could rise to the ignition temperature of magnesium.

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Figure 1—Fault Current vs. Maximum Allowed Bonding Resistance in the Presence of

Flammable Vapors or Liquids

FAULT

CURRENT

(AMPS)

MAXIMUM

ALLOWABLE

RESISTANCE

(MILLIOHMS)

HAZARD

RESISTANCE

(MILLIOHMS)

30 3.6 18

49 1.86 9.3

58 1.54 7.7

100 0.74 3.7

200 0.37 1.85

1000 0.074 0.37

5000 0.0148 0.074

-+-HAZARD RESISTANCE

(MILLIOHMS)

◄~ ---MAXIMUM ALLOWABLE

"- RESISTANCE (MILLIOHMS) -V')

:c:

...J

11. ~

...J

I ., w u z I-

IL. "'--

V')

V') w er:::

0.1

' t,,.., ' ~ ~ i,,,., --- i,,,., r"-1 I O.Ql

10 100 1000 10000

FAULT CURRENT (AMPS)

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4.1.3.1 Hazardous Area Bonding

[EBR 18] Electrical bonding of equipment or vehicle structure in areas where flammable materials, gases, or vapors may be present shall be adequate to prevent ignition due to conditions including heating, sparking, or arcing.

a. [EBR 19] The resistance of bond joints in such areas shall not exceed the Maximum

Allowable Resistance curve shown in figure 1.

4.1.4 Electromagnetic Interference or Radio Frequency (Class R)

The intent of Class R bonding is to provide a uniform low impedance path for all electrical equipment at radio frequencies. Refer to Appendix B.3.4 for more information.

a. [EBR 20] All electrical and electronic equipment shall be bonded using the methods described in section 5.1 to provide a low impedance path from the equipment enclosure to structure.

b. [EBR 21] All Class R bond paths to structure, and the joints in that path, shall be designed such that the inductance and overall impedance, including resonances, are low enough to prevent interference at the frequencies of interest.

(1) [EBR 22] The direct current (dc) resistance across each joint in the path shall not exceed 2.5 milliohms.

c. [EBR 23] The design and construction of the outer mold line of the vehicle shall implement Class R electrical bonding between all outer mold line components so as to inherently provide a uniform low impedance enclosure surrounding the vehicle.

d. [EBR 24] Hatches, access panels, doors, and other apertures in outer mold line components shall have at minimum a Class R electrical bond to the outer mold line material.

e. [EBR 25] Vehicle structural elements shall have a Class R electrical bond between elements, as well as between structural elements and outer mold line components, so that the entire structure of the vehicle is interconnected with uniform low impedance.

4.1.4.1 Electrical Connectors and Shield Termination

a. [EBR 26] Electrical connectors and their backshells that may be used to terminate cable shields shall be installed to provide a low impedance path from the backshell to the equipment case.

b. [EBR 27] The dc resistance for each joint in the backshell-to-case path shall not exceed 2.5 milliohms.

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Examples of such joints include between shield and backshell, backshell and connector, harness connector and enclosure connector, and enclosure connector and equipment enclosure.

4.1.4.2 Antennas

[EBR 28] Antennas that require low impedance to the ground plane for proper operation shall meet Class R requirements.

4.1.5 Lightning Protection (Class L)

Protection against lightning strikes should be provided for launch vehicles and their payloads during transportation, storage, prelaunch, launch, and landing. Propellant, pyrotechnics, and electronic equipment are particularly susceptible to direct and indirect effects of lightning. Refer to Appendix B.3.5 for more information.

a. [EBR 29] To distribute the current around the vehicle and minimize the currents near possible entry points into the vehicle and near critical areas and systems (including pyrotechnic systems, rocket motors, fuel handling and storage areas, antennas, electronic equipment, and signal and power cables), multiple low impedance paths shall be incorporated across and through vehicle outer mold line and structural components.

(1) [EBR 30] The dc resistance of all such joints shall be no greater than 2.5 milliohms.

All joints in vehicle outer mold line components should be designed to present the minimal impedance achievable to the lightning currents that may pass across the joint.

b. [EBR 31] Each electrical bond shall be bonded using the methods described in section 5.1, have low resistance and adequate contact area to carry its share of lightning current without sustaining a burning, melting, distorting, or other heating effect due to the long duration, high-current portion of the lightning strike.

(1) [EBR 32] The bonds shall have low impedance to prevent arcing and coupling of voltage spikes into electronic circuits due to the fast rise time portion of the lightning strike.

c. [EBR 33] The dc resistance of all joints and connections from hatches, access panels, doors, and other apertures in outer mold line components (expected to carry high amplitude lightning currents) shall be no greater than 2.5 milliohms.

Hatches, access panels, doors, and other apertures in outer mold line components expected to carry high amplitude lightning currents should be bonded with multiple low impedance connections to minimize aperture size and slot length.

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d. [EBR 34] Shield terminations, connectors, or connector backshells of electrical cables that are in the lightning current path, shall be capable of carrying expected lightning currents without damage.

Electrical cables that are outside the vehicle mold line or that could carry the lightning current should be completely enclosed in gross overshields with a circumferential 360 degree termination into bulkhead penetrations, connectors, or connector backshells.

(1) [EBR 35] The dc resistance of each such shield termination shall not exceed 2.5

e. [EBR 36] All paths shall be designed using zoning information developed in accordance with SAE-ARP-5414, Aircraft Lightning Zoning, supplemented by analysis employing lightning current waveforms defined in SAE-ARP-5412, Aircraft Lightning Environment and Related Test

Waveforms.

All paths should exhibit the minimal impedance achievable in each path.

f. [EBR 37] The voltage developed across any joint in the lightning current path shall not exceed 500 volts.

g. [EBR 38] Each bond in the lightning current path shall be capable of carrying expected lightning current.

4.1.5.1 Hazardous Area Bonding

a. [EBR 39] Fuel and pyrotechnics shall be completely enclosed by a Faraday cage of conductive material bonded to structure.

b. [EBR 40] Pyrotechnics cables and device connector shields shall have 360-degree bonded termination to the metal enclosure/backshell.

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4.1.6 Electrostatic Discharge (Class S)

[EBR 41] All conducting items, except active antenna elements, having any linear dimension greater than 7.6 centimeters (cm), which are subject to precipitation static effects, triboelectric effects, fluid flow, air flow, space and launch vehicle charging, separation of elements, and other charge generating mechanisms, shall have a mechanically secure electrical bond path to vehicle structure using the methods described in section 5.1.

See Appendix B.3.6 for more information.

a. [EBR 42] The resistance across the connection shall be 1.0 ohm or less.

A mechanically secure electrical bond path is a continuous bond path that maintains the default dc resistance (or lower) after exposure to shock, vibration, launch loads, and other expected mechanical movement.

A limit of 1.0 ohm is used as a requirement because it is easily obtained with good contact between conductive surfaces. Static charges can usually be dissipated through less conductive connections.

b. [EBR 43] When performing an analysis to determine acceptable values for Class S electrical bonds, the stored energy determined by the analysis shall be less than applicable hazard threshold levels for personnel shock, equipment upset, flammable materials, gases, or vapors, or electro-explosive device (EED) ignition for approval of the proposed electrical bond resistance.

Higher dc resistance values acceptable for Class S electrical bonds may be determined through performance of a detailed analysis to determine the amount of stored energy on the item to be bonded as a function of the proposed electrical bond resistance.

(1) [EBR 44] All conductive coatings, including those used to treat dielectric surfaces, shall be electrically bonded to the vehicle structure with a dc resistance of less than

105 ohms.

Launch services providers may levy flight vehicle surface conductivity requirements. See

Appendix B.3.6 for more information.

4.1.6.1 Multilayer Insulation

a. [EBR 45] All conductive layers of multilayer insulation with an area greater than 100 square cm shall be electrically bonded together.

(1) [EBR 46] Provisions shall be made for attachment to the vehicle structure.

A. [EBR 47] The conductive attach points shall be bonded directly to the

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B. [EBR 48] Two attach points to the structure per blanket shall be used for redundancy.

C. [EBR 49] Resistance from attach points to the structure shall be 1.0 ohm or less.

b. [EBR 50] Multilayer insulation with an area greater than 100 square cm shall have a minimum of one bond connection to the vehicle structure.

c. [EBR 51] Multilayer insulation with an area greater than 1,000 square cm shall have a minimum of two bond connections to the vehicle structure.

d. [EBR 52] A minimum of one additional bond connection to the vehicle structure shall be made for each increase of 40,000 square cm.

e. [EBR 53] Multilayer insulation consisting of two or more sections shall have all sections electrically bonded to each other.

(1) [EBR 54] The contiguous insulation thus formed shall be considered as one section of insulation for determination of the number of bond tabs.

4.1.6.2 Hazardous Area Bonding

a. [EBR 55] All conductive items in areas where flammable materials, gases, or vapors may be present shall have a Class S electrical bond not to exceed 1.0 ohm.

(1) [EBR 56] In no case shall any such electrical bond be inadequate to prevent ignition due to heating or arcing.

b. [EBR 57] Specific Class S electrical bond values in hazardous areas shall be determined through performance of a detailed analysis to determine the amount of stored energy on the item to be bonded as a function of the proposed electrical bond resistance.

(1) [EBR 58] The stored energy determined by the analysis shall be 1/10 of applicable minimum ignition energy (MIE) (or 20 decibels (dB) below) threshold level for the flammable materials, gases, or vapors that may be present.

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4.1.6.3 Pipe, Tubing, and Hoses

a. [EBR 59] All metallic pipes, tubes, and hoses that carry fluids shall have a mechanically secure connection to the structure that will measure 1.0 ohm or less.

b. [EBR 60] Nonmetallic plumbing installations shall be designed so that the static voltage, generated by fluid flow, will not exceed 350 volts at any point outside the pipes, tubes, or hoses.

c. [EBR 61] The resistance of nonmetallic hoses shall not exceed 1.0 megohm per meter of length to dissipate charges developing within the fluid or between fluid and the hose.

5. DETAILED REQUIREMENTS

5.1 Bonding Methods

The following paragraphs describe the bonding methods, with the metal-to-metal method being the preferred method. The metal-to-metal method may not be feasible, and the bonding strap or fastener method may be the best bonding alternative for the application.

5.1.1 Metal-to-Metal (faying surface to faying surface)

Equipment and structure with metal-to-metal joints that are joined by processes that transform the mated surfaces into one piece of metal, such as by welding or brazing, are considered permanent and inherently bonded.

a. [EBR 62] Semi-permanent joints held together by screws, rivets, clamps, etc., shall have their faying surfaces prepared prior to assembly in accordance with paragraph 5.2 to ensure a good electrical bond.

(1) [EBR 63] Clamping pressure across semi-permanent joints shall be in accordance with applicable mechanical engineering assembly and installation requirements.

5.1.2 Bond Straps

Where the direct joining of structural elements, assemblies, and electrical paths is impossible or impractical, bonding straps or jumpers may be used.

Bond straps or jumpers may be used to meet Class C, H, or S bonding requirements, and are useful for some cases in Class L.

The usefulness of bond straps for Class R bonds is very limited, and should be used only as a last resort and with approval by the procuring agency.

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a. [EBR 64] Bonding straps installed across shock mounts or other suspension or support devices shall not impede the performance of the mounting device.

(1) [EBR 65] The bond straps shall be capable of withstanding the anticipated motion and vibration requirements without suffering metal fatigue or other failure.

Extra care should be utilized in the attachment of the ends of bonding straps to prevent arcing or other means of electrical noise generation with movements of the strap.

b. [EBR 66] For Class R bonds, the bonding straps shall be as short as possible.

(1) [EBR 67] The bond straps shall be flat in cross-section.

(2) [EBR 68] The bond straps shall have a length-to-width ratio of less than 5 to 1 to minimize the inductance of the strap.

c. [EBR 69] For Class L application of bond straps, the bond straps or jumpers shall be as short as possible.

(1) [EBR 70] The bond straps shall have adequate lug contact area and adequate wire/lug cross-sectional area to carry the lightning current.

(2) [EBR 71] The cross-sectional area of any individual jumper shall not be less than number 12 American Wire Gauge (AWG) wire (6530 circular mils) for stranded copper, and not less than number 10 AWG wire (10,380 circular mils) for stranded aluminum.

These wire sizes are only valid when two or more jumpers are installed to carry lightning current and when the jumpers are not subject to a direct arc.

(3) [EBR 72] Where the jumper is subject to arcing, a minimum of number 7 AWG

(20,820 circular mils) for copper or number 5 AWG (33,100 circular mils) for aluminum for each jumper shall apply.

(4) [EBR 73] The jumper shall be robust enough to withstand magnetic forces caused by the high current through the strap.

(5) [EBR 74] The jumper shall not rely on soldered connections to carry lightning

For multistroke protection or if arcing at the jumper is expected, the total cross-sectional area of the straps should be 40,000 circular mils or greater.

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5.1.3 Fasteners

If the bond application is approved by the procuring agency, fasteners (e.g., bolts, nuts, or studs) may be used to meet bonding requirements. Fasteners should be primarily used to maintain pressure on faying surfaces. However, in some cases fasteners may perform better than straps for Class L and R applications. The inductance of multiple bolts between otherwise isolated materials may be less than the inductance of a strap between surfaces.

a. [EBR 75] When bolts are used as part of the bond path, an analysis shall be performed showing that the number of bolts used in the path is sufficient to provide a low impedance path.

b. [EBR 76] Fasteners shall be sealed against moisture and air to prevent corrosion of the threads.

Rivets are acceptable if a minimum of three rivets is used per junction and they are match-drilled.

c. [EBR 77] The following are problematic and shall not be used for electrical bonding purposes:

(1) Self-tapping screws.

(2) Zinc-plated bolts, nuts, or screws.

(3) Star, anodized, or zinc-plated washers.

(4) Cadmium-plated hardware.

d. [EBR 78] For Class L applications, multiple rivets, bolts, or other fasteners shall be used at joints in vehicle skin and structure to ensure multiple metallic contact areas capable of sharing lightning current.

5.2 Surface Cleaning and Finishing

a. [EBR 79] The faying surfaces of all electrically bonded metal-to-metal joints shall be cleaned of all nonconductive materials and protected against corrosion.

b. [EBR 80] The finishes and protection methods for faying surfaces shall be per

NASA-STD-6012, Corrosion Protection for Space Flight Hardware, and NASA-STD-6016, Standard Materials and Processes Requirements for Spacecraft.

(1) [EBR 81] The protection method or finish selected shall not negate the electrical bond between the two surfaces.

c. [EBR 82] Treated mating surfaces shall be protected by packaging materials or protective films until just prior to mating.

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d. [EBR 83] After protective material is removed, the surfaces shall be cleaned by blowing, vacuuming, or wiping with appropriate solvent as necessary to remove dust or other foreign particles before mating.

Non-hardening sealant or thermal grease may be applied to the faying surfaces of semi-permanent joints if tests indicate bonding requirements can be met after assembly.

If the bond is permanent, a hardening sealant, such as chromated epoxy primer, may be used if tests indicate bonding requirements can be met after assembly.

e. [EBR 84] Surfaces that are expected to remain mated indefinitely shall be inspected periodically to ensure a good electrical bond is maintained.

5.3 Galvanic Corrosion of Dissimilar Materials

Direct contact of dissimilar materials in the presence of moisture may result in corrosion, which impairs the effectiveness of any electrical bond and weakens the structure in which it occurs.

When choosing materials for a given electrical bonding application, major factors that contribute to corrosion are the degree of separation of metals in the galvanic series and the amount of moisture present.

a. [EBR 85] Corrosion control of galvanic couples shall be in accordance with NASA-

STD-6012 and NASA-STD-6016.

Refer to Appendix B.3.7 for more information.

5.4 Carbon Fiber Reinforced Plastic

Carbon fiber reinforced plastic (CFRP) provides some conductivity through the graphite filaments. However, the graphite is usually covered with nonconductive epoxy or phenolic material.

a. [EBR 86] CFRP shall be bonded to control electrostatic discharge (ESD) and may be useful as an RF bond.

b. [EBR 87] CFRP shall not be used in a Class C or Class H bond path.

The procedure for bonding CFRP requires removing enough nonconductive material from the mating surfaces to expose the graphite layer. Electrical bonds between CFRP sheets can be made by overlapping exposed graphite on both sheets. Conductive epoxy may also be placed on the exposed graphite, and bonding connections may be made to metallic surfaces through the conductive epoxy.

NOTE: A fire hazard exists with current flow through graphite epoxy materials.

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5.5 Verification

a. [EBR 88] Verification of electrical bonding requirements shall be accomplished by a combination of tests, similarity, analysis, and inspection.

b. [EBR 89] The extent of verification and the methods used shall be defined for each program.

Some requirements should be verified at the equipment level, such as bonding of equipment assembly interfaces and connector backshell contacts.

The resistance of bonds may be measured on flight vehicles, but it is usually impractical to measure inductance or current carrying capability.

Verifying each joint in a bond path is not always feasible and therefore an end-to-end measurement may be an option. Controls need to be implemented in shield termination paths through connector assemblies. A realistic value would be on the order of 10 milliohms from the shield to the electronics enclosure for a cadmium-plated aluminum assembly, with 2.5 milliohms maximum for any particular joint.

c. [EBR 90] The resistance requirement of all classes of bonds shall be verified by testing sample bonds.

Other bonds of the same type, using the same procedures, may be verified by similarity.

d. [EBR 91] Spot checks shall be made to verify the process is still good and is being followed.

e. [EBR 92] The current carrying capability of Class C, H, and L bonds shall be verified by analysis and inspection.

Class C, H, and L bonds require current carrying capability, as well as low resistance contacts.

f. [EBR 93] Low inductance paths of Class R and Class L bonds shall be verified by analysis and inspection.

Class R and Class L bonds require low inductance paths as well as low resistance.

g. [EBR 94] For flight vehicle surfaces that have been treated with conductive coatings

(4.1.6.b.1), test or analysis shall show that the bonding requirements are met.

(1) [EBR 95] Relaxation of this requirement shall only be granted if it has been clearly verified by test or analysis that electrostatic charges deposited on the surface of the vehicle will not be hazardous to the flight vehicle or the launch mission.

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h. [EBR 96] If flight vehicle surface conductivity requirements are imposed (4.1.6.b.2), the flight vehicle surface material resistivity requirements shall be verified through test or analysis.

(1) [EBR 97] Relaxation of this requirement shall only be granted if it has been clearly verified by test or analysis that electrostatic charges deposited on the surface of the vehicle, caused by triboelectrification from precipitation particle impact, will not be hazardous to the flight vehicle or the launch mission.

Flight vehicle includes the launch vehicle itself, the payload (if the payload outer surfaces are exposed to the triboelectrification process), and fairings or shrouds protecting payloads.

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APPENDIX A

REQUIREMENTS COMPLIANCE MATRIX

A.1 Purpose

This appendix provides a listing of requirements contained in this NASA Technical Standard for selection and verification of requirements by programs and projects. (Note: Enter “Yes” to describe the requirement’s applicability to the program or project; or enter “No” if the intent is to tailor, and enter how tailoring is to be applied in the “Rationale” column.)

NASA-STD-4003A w/Change 1

Section Description Requirement in this Standard

Applicable

(Yes or

No)

If No, Enter

Rationale

1.3 Tailoring [EBR 1] Tailoring of this NASA Technical Standard for application to a specific program or project shall be formally documented as part of program or project requirements and approved by the responsible Technical Authority in accordance with NPR 7120.5, NASA Space Flight Program and

Project Management Requirements.

2.1.1 Applicable

Documents

[EBR 2] The latest issuances of cited documents shall apply unless specific versions are designated.

2.1.2 Applicable

Documents

[EBR 3] Non-use of specifically designated versions shall be approved by the responsible Technical

Authority.

2.4.2 Order of Precedence [EBR 4] Conflicts between this NASA Technical Standard and other requirements documents shall be resolved by the responsible Technical Authority.

4.1 Electrical Bonding [EBR 5] There may be more than one purpose for bonding a specific interface, and the bond shall meet the requirements of each applicable class.

4.1.1 Assembly Drawings [EBR 6] Notes shall be provided on assembly drawings indicating the applicable class or classes.

4.1.2 Power Current Return

Path (Class C)

[EBR 7] All circuits and systems that use vehicle structure for a power return path shall satisfy

Class C bonding requirements.

4.1.2.1a Bond Joints [EBR 8] The total voltage drop across all electrical bond joints between the power supply and the load shall be controlled to keep the voltage within the tolerance of the applicable power quality standard.

4.1.2.1b Bond Joints [EBR 9] If no power quality standard is applicable, a default voltage drop value of 3.5 percent of the operating bus voltage shall be used.

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Section Description Requirement in this Standard

Applicable

(Yes or

No)

If No, Enter

Rationale

4.1.2.2 Magnesium Alloy [EBR 10] Magnesium alloy structure shall not be used as an intentional current return path.

4.1.2.3a Hazardous Area

Bonding

[EBR 11] Electrical bonding of equipment or vehicle structure in areas where flammable materials, gases, or vapors may be present shall be adequate to prevent ignition due to heating, sparking, or arcing.

4.1.2.3b Hazardous Area

Bonding

[EBR 12] The resistance of bond joints in hazardous areas shall not exceed the Maximum

Allowable Resistance curve shown in figure 1, Fault Current vs. Maximum Allowed Bonding

Resistance in the Presence of Flammable Vapors or Liquids.

4.1.2.4 Pipe, Tubing, and

[EBR 13] Pipes, tubing, and hoses shall not be used as an intentional return path for electrical

4.1.3a Shock and Fault

Protection (Class H)

[EBR 14] Exposed cases or chassis of electrical or electronic equipment shall be bonded to structure with a resistance of 0.1 ohm or less using the methods described in section 5.1.

4.1.3b Shock and Fault

[EBR 15] Metallic conduit, cable trays, and other conductive objects susceptible to short circuits shall have a resistance to structure of 0.1 ohm or less.

4.1.3c Shock and Fault

[EBR 16] For personnel and fire safety, the fault current return path shall be capable of conducting a minimum of 500 percent overload current for a time period of 0.5 second.

4.1.3d Shock and Fault

[EBR 17] Magnesium alloy structure shall not be used as a primary fault current return path.

4.1.3.1 Hazardous Area

Bonding

[EBR 18] Electrical bonding of equipment or vehicle structure in areas where flammable materials, gases, or vapors may be present shall be adequate to prevent ignition due to conditions including heating, sparking, or arcing.

4.1.3.1a Hazardous Area

[EBR 19] The resistance of bond joints in such areas shall not exceed the Maximum Allowable

Resistance curve shown in figure 1.

4.1.4a Electromagnetic

Interference or Radio

Frequency (Class R)

[EBR 20] All electrical and electronic equipment shall be bonded using the methods described in section 5.1 to provide a low impedance path from the equipment enclosure to structure.

4.1.4b Electromagnetic

Frequency (Class R)

[EBR 21] All Class R bond paths to structure, and the joints in that path, shall be designed such that the inductance and overall impedance, including resonances, are low enough to prevent interference at the frequencies of interest.

4.1.4b(1) Electromagnetic

Frequency (Class R)

[EBR 22] The direct current (dc) resistance across each joint in the path shall not exceed 2.5

4.1.4c Electromagnetic

Frequency (Class R)

[EBR 23] The design and construction of the outer mold line of the vehicle shall implement Class R electrical bonding between all outer mold line components so as to inherently provide a uniform low impedance enclosure surrounding the vehicle.

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Section Description Requirement in this Standard

Applicable

(Yes or

No)

If No, Enter

Rationale

4.1.4d Electromagnetic

Interference or Radio

Frequency (Class R)

[EBR 24] Hatches, access panels, doors, and other apertures in outer mold line components shall have at minimum a Class R electrical bond to the outer mold line material.

4.1.4e Electromagnetic

Frequency (Class R)

[EBR 25] Vehicle structural elements shall have a Class R electrical bond between elements, as well as between structural elements and outer mold line components, so that the entire structure of the vehicle is interconnected with uniform low impedance.

4.1.4.1a…