FAA-STD-020 Transient Protection GBS Reqmts for Electronic Eqpt.pdf

FAA-STD-020 R E V B 9003327 0009377 381

-, F y a’, May €1, 1992

SUPERSEDING

FAA-STD-O20a, 09/26/85 m?SPP-o20b

TRANSIENT PROTECTION, GROUNDING, BONDING AND SHIELDXNG

REQUIREMENTS FOR ELECTRONIC EQUIPMENT

Provided by IHS Licensee=FAA NAS/6110654001 Not for Resale, 07/13/2006 12:10:36 MDTNo reproduction or networking permitted without license from IHS

FAA-STD-O2Ob Hay Il, 1992

F A A - S T D - O Z O R E V B 9003329 0009378 2L8

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T h i s FAA s t a n d a r d sets f o r t h r equ i r emen t s f o r t h e a p p l i c a t i o n of t r a n s i e n t p r o t e c t i o n , grounding, bonding, s h i e l d i n g and p e r s o n n e l p r o t e c t i o n practices t o t h e dea ign , f a b r i c a t i o n and assembly o f e l e c t r o n i c equipment. The e l e c t r o m a g n e t i c i n t e r f e r e n c e ( E M ) r equ i r emen t s related t o t h e s e d i s c i p l i n e s are also provided. T h i s s t anda rd s h a l l be a p p l i e d t o new e l e c t r o n i c equipnent or as m o d i f i c a t i o n s are made t o e x i s t i n g e l e c t r o n i c equ ipnen t .

T h i s standard c o n t a i n s 6 sections. S e c t i o n 1 states t h e scope o f t h e s t a n d a r d and g i v e s i t s purpose. S e c t i o n 2 l ists t h e r e f e r e n c e documents. S e c t i o n 3 g i v e s r equ i r emen t s f o r t r a n s i e n t p r o t e c t i o n , grounding , bonding, s h i e l d i n g and pe r sonne l p r o t e c t i o n .

S e c t i o n 5 prov ides P r e p a r a t i o n f o r d e l i v e r y in fo rma t ion . S e c t i o n 6 c o n t a i n s n o t e s and d e f i n i t i o n s .

Section 4 p r o v i d e s Q u a l i t y Assurance r equ i r emen t s .

The u s e of " s h a l l " i n t h i s document i n d i c a t e s a r equ i r emen t . I t is unders tood t h a t i n c e r t a i n cases it may n o t be t e c h n i c a l l y f e a s i b l e t o implement c e r t a i n r equ i r emen t s .

c o n t r a c t documents or i n t h e equipment drawings.

I n these cases exemptions s h a l l be documented as part of

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CONTENTS

Paragraph T i t l e Page

1. S C O P E

1.1 SCODe

1.2 PurDose

2. APPLICABLE DOCUMENTS

2.1 Government documents

2.2 Non-Government documents

3. WQUIREMENTS

3.1 Surae and t r a n s i e n t p r o t e c t i o n r eau i r emen t s

3.2 E x i s t i n a e l e c t r o n i c eauimnent d e s i a n s

3.3 I n s t a l l a t i o n bv others

3.4 E l e c t r o n i c e a u i m e n t t r a n s i e n t S u s c e D t i b i l i t v levels

3.5 Conducted = w e r i n p u t l i n e t r a n s i e n t s

3.5.1 S u r a e l e v e l s

3.5.2 P r o t e c t i o n d e s i s n

3.5.3 F u n c t i o n a l r eau i r emen t s

3.5.4 Packaa inq

3.6 Power S U D D ~ V t r a n s i e n t su rmress ion

3.7 Conducted l a n d l i n e t r a n s i e n t s

3.7.1 T r a n s i e n t levels

3.7.2 Loca t ion of t r a n s i e n t p r o t e c t i o n

3.7.3 P r o t e c t i o n d e s i s n

3.7.4 F u n c t i o n a l r eau i r emen t s

3.7.5 I n s t a l l a t i o n a t f a c i l i t v e n t r a n c e

3.7.6 I n s t a l l a t i o n a t t h e e l e c t r o n i c eauiDment

3.7.7 E x t e r n a l l y mounted e a u i m e n t

3.7.8 A x i a l l a n d l i n e s

3.7.8.1 P r o t e c t i o n d e s i a n

3.7.8.2 Metal bulkhead connec to r d a t e s

3.7.0.3 i n s t a l l a t i o n a t f a c i l i t v e n t r a n c e s

3.7.8.4 I n s t a l l a t i o n a t e l e c t r o n i c e a u i m e n t e n t r a n c e s

3.7.9 F i b e r opt ics cable

3.8 Groundina r e w i r e r t e n t s

3.8.1 Genera l

3.8.2 EqUiDment r e a u i r i n a e l e c t r o n i c s i n a l e a rounds

3.8.2.1 E l e c t r o n i c s ina l e -Do in t a round system

3.8.2.2 Inpu t and outDut s i a n a l s

3.8.2.3 E l e c t r o n i c s i n a l e - w i n t a round t e n n i n a l l s l . . 10

3.8.2.4 I s o l a t i o n

3.8.2.5 E l e c t r o n i c s i a n a l l i n e s and cables

3.8.2.6 Terminat ion o f i n d i v i d u a l s h i e l d s

3.0.2.7 Terminat ion of overal l s h i e l d s

3.8.2.8 S i n a l e - w i n t a round ina of e l e c t r o n i c e a u i m e n t

3.8.3 M u l t i w i n t a round inu of e l e c t r o n i c e t n i m e n t

3.8.3.1 E l e c t r o n i c s i a n a l r e t u r n Dath

3.8.3.2 S h i e l d t e r m i n a t i o n s of coaxial and o t h e r cables f r eauencv c i r c u i t s

3.0.4.1 Inuu t and o u t m t electronic s i a n a l s

3.8.5 E l e c t r o n i c c a b i n e t , r ack . and case a r o u n d i n q

3.8.5.1 Mountina s u r f a c e s . . . . . . . . . . . . . . 1 5

3.0.6 Euuiunent a round ina conduc to r

3.8.4 E l e c t r o n i c ecniimnent con ta in ina b o t h l o w and h i a h

I

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3.8.7 PeceDtacles

3.8.8 &C powerline isolation

3.8.9 portable eauiwnent

3.8.10 pa ult protection

3.8.10.1 petal control shafts

3.8.10.2 Shielded comDartments

3.8.11 Powerline filters

3.8.12 Gr oundina of RF transmission lines and antennas . . .

3.9 Bondina reuuirements

3.9.1 Genera4

3.9.2 Methods

3.9.2.1 Welding

3.9.2.2 Solderinq

3.9.2.3 Boltinq

3.9.2.4 Rivetinq

3.9.2.5 Sheet metal screws

3.9.2.6 Bondina straps

3.9.3 Surface preParation

3.9.3.1 Machined surfaces

3.9.3.2 Surface Platinas or treatments

3.9.4 pissimilar metals

3.9.5 pond protection

3.9.5.1 corrosion Protection

3.9.5.2 Vibration

3.9.6 Bondina across shock mounts

3.9.7 Enclosure bondins

3.9.7.1 Subassemblies

3.9.7.2 Euuioment

3.9.0 Connector mountinq

3.9.9 Shield terminations

3.9.10 RF aaskets

3.9.11 Bond resistance

3.10.1 General

3.10.2 Electromaanetic environment control

3.10.2.1 Materials

3.10.2.2 Gaskets

3.10.2.3 Filter intearation

3.10.2.4 Control of anertures

3.10.2.5 Bondina and aroundina of compartment

shields

3.10.2.6 Wire and cable routing

3.10.2.7 Circuit layout

3.11 personnel Drotection remirements

3.11.1 General

3.12.1 General

3.12.2 Controlled areas

3.12.3 Circuit and eauiwnent desian

3.12.4 packauina and storaae

3.12.6 Tools and accessories

3.12.7 p r niture and UDholsterv

3.12.10 Jon aeneration

4.1 plectromaanetic comoatibiïitv and cnialitv assurance

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.10 Shieldina reauirements

. . . . . . . . . . . . . . . . 3.12 Control of static electricity

. . . . . . . . . . . . . . . . . . . . 3.12.5 Work surfaces

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.12.0 Shoes and clothinq

3.12.9 printers

4 . QUALITY ASSURANCE PROVISIONS . *

. . . . . . . . . . . . . . . . . . . . . . 4.1.1 General %

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-V- FAA-STD-O2Ob May 11. 1992

4.2 Reauirements

4.3 ADDrOVal

5 . PREPARATION FOR DELIVERY

5.1 General

6 . NOTES

6.1 Definitions

6.1.1 Bond

6.1.2 Bond . direct

6.1.3 Bond. indirect

6.1.4 Bondinq

6.1.5 Bondinu iumoer

6.1.6 Brazinq

6.1.7 Buildinq

6.1.8 Cabinet

6.1.9 Case

6.1.10 Chassis

6.1.11 ClamD voltaae

6.1.12 Conductor . bare

6.1.13 Conductor . insulated

6.1.14 Crowbar

6.1.15 Electromaunetic interference (EXIL

6.1.16 Eauiment aroundina conductor

6.1.17 EauiDment . unit or Diece of

6.1.18 Facility around svstem

6.1.19 Ground

6.1.20 Grounded

6.1.21 Grounded conductor

6.1.22 Grounded. effectivelv

6.1.23 Groundinu conductor

6.1.24 Hiqh freuuencv

6.1.25 Landline

6.1.26 Low freuuencv

6.1.27 Electronic multiwint around svstem

6.1.28 Overshoot voltaae

6.1.29 Rack

6.1.30 Reference Dlane or mint . electronic sianal

6.1.31 Reverse standoff voltacre

6.1.32 Shield

6.1.33 Electronic sinule-point around svstem

6.1.34 Structure

6.1.35 Transient sumressor

6.1.36 Turn-on voltaue

6.1.37 Surae

6.1.38 Transient

6.1.39 Susceptibilitv level

6.2 Acronvms and abbreviations

6.3 Guidelines

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2 .

3 .

4.

LIST OF ILLUSTRATIONS

Typical Protection Configurations for Electronic Equipment from

Single Point Grounding for Individual Unit or Piece of Electronic Equipment

Single Point Electronic Ground Bue Bar Installation in Rack or Cabinet

Conducted Powerline Surges and Transients

Bonding of Connectors to Mounting Surface

LIST OF TABLES

I. Line-to-Ground Surge Levels for 120 VAC Powetlines II. Conducted Landline Transient Levels t

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FAA-STD-020 REV B

1. SCOPE

W 9003329 0009383 685

-1- FAA-STD -02 Ob May Il, 1992

1.1 Scom. This document defines standard configurations and procedures, for transient protection, grounding, bonding, shielding and personnel protection, for new electronic equipment used to support air traffic control €unctions.

In addition, it may be used as reference information, without imposing minimum or mandatory requirements for existing electronic equipment.

1.2 Purwse. The requirements of this standard are intended to minimize electrical hazards to personnel and minimize damage to equipment due to lightning, transients, and power faults, and also to minimize electromagnetic interference.

2. APPLICABLE DOCUMENTS

2.1 Government documents. Issues of the following documents in effect on the date of an invitation-for-bid or request-for-proposals, form a part of this standard. They are applicable only to the extent specified herein. If conflicts occur between these referenced documents and this standard, the standard shall provide the superseding requirement.

FAA Specifications:

FAA-G-2 100 Electronic Equipment, General Requirements

FAA Standards:

FAA-STD-019 Lightning Protection, Grounding, Bonding and Shielding Requirements for Facilities

FAA-STD-012 . Paint Systems fo r Equipment

FAA Orders:

Order 6950.19 Practices and Procedures for Lightning Protection, Grounding, Bonding and Shielding Implementation.

Protection, Grounding, Bonding & Shielding.

Order 6950.20 Fundamental Considerations of Lightning

(Copies of these specifications, standards, orders and other applicable FAA documents may be obtained from the Contracting Officer issuing the invitation-for-bids or request-for-proposals. Requests should fully identify material desired, i.e. specification, standard, amendment, drawing numbers and dates. Requests should cite the invitation-for-bids, request-for-proposals, the contract involved, or other use to be made of the requested material.)

Militarv Standards and Handbooks:

DOD-HDBK-263 Electrostatic Discharge Control Handbook

DOD-STD-1686 Electrostatic Discharge Control Program for Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices)

Program Requirements MIL-HDBK-237 Electromagnetic Compatibility/Interference

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9003329 0009384 511

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MIL-HDBK-253 Guidance for Design and Test of Systems Protected Against Effects of Electromagnetic Energy

MIL-STD-461 Electromagnetic Interference Characteristics, Requirements for Equipment8

MIL-STD-889 Dissimilar Metals

(Single copies of Military specifications, standards, and handbooks may be requested by mail or telephone from the Naval Forms and Publications Center, 5801 Tabor Ave, Philadelphia PA 19120. Not more than five items may be ordered on a single request; the Invitation for Bid or Contract Number should be cited where applicable. Only latest revisions (complete with latest amendments) are available; slash sheets must be individually requested.

Request all items by document number. For subscription service information, direct inquiries to the above address with additional marking (ATTN: CODE 56.)

2.2 Non-Government documents. Refer to para. 2.1, Government Documents.

National Fire Protection Association (NFPA).

NFPA 70 National Electrical Code (NEC)

NFPA 77 Static Electricity

(Requests €or copies of the National Electrical Code should be addressed to the National Fire Protection Association, Batterymarch Park, Quincy, MA 02269.)

3. REQUIREMENTS

3.1 Surae an¿ transient nrotection recniirements. Electrical and electronic equipment shall be protected against conducted and radiated surges and transients from all power, signal, control and/or status lines. Integrated circuits, transistors, diodes, solid state voltage regulators, capacitors, miniature relays, miniature switches, and miniature transformers, etc. are quite susceptible to damage and operational upset caused by transients.

3.2 Existina electronic euuiDment desians. For existing electronic equipment designs, transient suppression specified, may be at line entrances to electronic equipment enclosures, racks, or cabinets, or externally mounted to electronic equipment enclosures using proper grounding, bonding, and shielding procedures.

3 . 3 Znstallation bv others. Electronic equipment that is not being installed by the manufacturer or supplier shall be provided with all items of material required for installation of transient protection, including complete installation and checkout instructions.

3.4 Electronic eauiunent transient susceutibilitv levels. The manufacturer shall perform analyses or tests to determine the voltage, current, or energy levels that will cause immediate damage to components, shortened its operating life, or cause operational upset. These analyses or tests shall consider all electrical and electronic equipment components exposed to the effects of surges or transients. The combined facility and equipment entrance protection shall be coordinated so as to limit transients at the equipment entrance to below the equipment susceptibility level. Requirements of this paragraph z

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-3- FAA-STD-020b Hay 11, 1992 shall be included in the comprehensive control and test plans outlined in para. 4. In all cases the following characteristics shall be evaluated:

(a) Component damaae threshold. The damage threshold is the transient parameter level that renders the component nonfunctional or operationally deficient. For solid state components, voltage is usually the relevant parameter.

(b) Component dearadation level. The transient voltage or energy level that, with repeated application, shortens the useful life of the component.

(c) ODerational upset level. The transient voltage or energy level that causes an unacceptable change in operating characteristics for a duration in excess of 10 milliseconds for analog equipment or a change of logical itate for digital equipment.

3.5 Conducted Dower inout line transients. Transient suppression devices, components or circuits shall be provided at the entrance of AC power conductors to the equipment where needed as an integral part of electronic equipment design. Transient suppression shall be provided equally for both neutral and phase (hot) conductors and shall protect in both the differential and common modes. Electronic equipment that is to be installed outside of facilities shall also require protection to the level supplied for the facility. (See FAA-STD-019, para. 3.7, Conducted powerline surges.)

3.5.1 Surae levels. Surge levels and number of occurrences for life cycle design of transient suppression are given in Table I. In Table I, the 10-by-20 microsecond ( p s ) waveform defines a surge with a risetime of 10 ps from zero to peak value that exponentially decays to 50 percent of peak value 20 ps after start of the surge. These devices shall be able to tolerate surges of shorter duration without malfunction.

TABLE I. LINE-TO-GROUND SURGE LEVELS FOR 120 VAC POWERLINES

Surge Amplitude Number of Surges 10-by-20 ps Waveform ( Lifetime )

SOOV, SOA 1,000

750V, 100A

IkV, 200A

3 . 5 . 2 Protection desian. A typical configuration for protection of electronic equipment from conducted powerline surges and transients is illustrated in Figure 1, "Typical Configuration for Protection of Electronic Equipment from Conducted Powerline Surges and Transients."

components shall be as follows:

(a) conducted by the varistor, RV1.

(b) The varistor, RVl, shall be selected to limit surge voltages safely below the equipment circuit susceptibility level. The varistor (zinc or metal oxide nonlinear resistor) shall have adequate current and energy ratings to safely conduct the surge levels listed in Table I. A varistor is illustrated as the

Selection of

The inductor L1 shall be selected to safely limit the transient current

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FAA-STD-020 R E V B 9003329 0009386 394 H

May Il, 1992

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ELECTRON I C

EQU I PMENT

POWERL I NE

ELECTRON I C

EQU I PMENT

C I R C U I T

1, - ELECTRON I C EQU I PMENT

CASE GROUND

a . TYPICAL TRANSIENT SUPPRESSION FOR AC

L I N E INPUT TO ELECTRONIC EQUIPMENT

ELECTRON I C

EQU I PMENT

I NPUT

NEUTRAL

A - ELECTRON I C

CASE GROUND

EQU I PMENT

b . TYPICAL TRANSIENT SUPPRESSION FOR AC

NEUTRAL INPUT TO ELECTRONIC EQUIPMENT

Figure 1. Typical Protection Configurations for Electronic Equipment from Conducted Powerline Surges and Transients.

suppression circuit device in Figure 1 because the characteristics of avail-able devices are suitable for many applications. Other suppression devices, such as silicone avalanche diode suppressors (SAS) , shall be used when their characteristics are better suited to specific applications. Protection of highly susceptible electronic equipment circuits may also require the parallel connection of two or more suppression devices, matched within one percent, or the addition of a second device separated by a properly sized inductor.

(ci Selection of these components may also consider the interference and susceptibility requirements of other specifications or standards.

The inductor L2 and capacitor C1 limit high frequency transient energy.

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3.5.3 Functional reauirements. The basic characteristics of aurge suppres-sion components or circuits for equipment powerlines shall be as follows:

(a) 0.D eratina (reverse standoffi voltaae. Reverse standoff voltage of the arrester shall be 125 f 5 percent of the normal line voltage.

(b) Turnon voltaae. Turnon voltage, discharge (clamp) voltage, and the amplitude and time duration of any overshoot voltage shall be sufficiently low to preclude electronic equipent damage or operational upset.

(c) Leakaae current. Leakage current for each suppression component at reverse standoff voltage shall not exceed 100 microamperes.

(d) Self-restorina capability. The surge suppressors shall automatically restore to an of€ state when surge voltage falls below the turnon voltage for the suppressor.

(e) Operatina lifetime. Electronic equipment surge suppression shall be capable of safely dissipating the number and amplitude of surges specified in Table I. Clamp voltage shall not change more than 10 percent over the operating lifetime.

(f) In-line devices. Only inductors designed to have low DC resistance shall be used as in-line devices for suppression of conducted powerline surges.

In-line inductors shall safely pass equipment operating voltages and line current with 130 percent over-voltage conditions for a period of 50 milliseconds. Inductors shall safely handle the number of events at the voltages and currents as listed in Table I.

3.5.4 Packaainq. Suppression components shall be housed in a separate, shielded, compartmentalized enclosure as an integral part of the electronic equipment design. Bulkhead-mounted feedthrough capacitors shall be used as necessary to prevent high frequency transient energy from coupling to electronic equipment circuits. Suppression components shall be grounded to the electronic equipment case as directly as feasible.

3.6 Power S U D D ~ V transient sumression. Power supplies that use 60 hertz (Hz) power and furnish operating voltages (5 to 48 VDC) to solid state equipment shall have transient suppression components installed line-to-ground at the power supply rectifier output. During conduction of transients, the suppressor shall not decrease rectifier output voltage below normal. The ground side of suppressors shall be connected as directly as possible to rectifier output ground. Operating characteristics of suppression components provided for power supply rectifier output lines shall be as follows:

(a) Operatina (reverse standoff) voltaae. Reverse standoff voltage shall be 5 percent above maximum rectifier output voltage.

(b) Leakaae current. Leakage current to ground shall not exceed 100 microamperes at reverse standoff voltage.

(c) Turnon voltaae.

as possible using state-of-the-art suppressors, and shall not exceed 125 percent of standoff voltage.

(d) Discharue tclamDi voltaae. Clamp voltage shall be the lowest possible value that can be obtained using state-of-the-art suppressors not exceeding 160 percent of standoff voltage.

Turnon voltage shall be as near reverse standoff voltage

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FAA-STD-020 R E V B 9003329 0009388 167

l O O V , SOA 1,000

SOOV, 100A 100

750V, 375A 50 lOOOV, 1000A 5 I

FAA-STD-O2Ob May 11, 1992

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(e) Overshoot voltaoe. Overshoot voltage shall be sufficiently low to preclude electronic equipment damage or operational upset.

overshoot voltage shall be limited to the shortest possible time not exceeding 2 nanoseconds.

(f) S e l f - r e s t o r i n a y . Transient suppressors installed in power supplies shall automatically restore to an off rtate when line transient voltage falls below rated turnon voltage for the ouppreeeor.

(9) - ratino lifetime. The transient suppressors shall safely dissipate 1000 surges with an amplitude of 200 volts above rectifier output voltage and a waveform of 10-by-20 pa. Ten (10) ps defines the time from the start of the transient to peak voltage, and 20 ps is the time from the start of the transient until the transient decays to 50 percent of peak value.

Time duration of

3.7 Conducted landline transients. Transient protection shall limit tran-sients at the equipment entrance to below the equipment susceptibility level.

Landlines include all signal, control, status and interfacility powerlines installed above and below grade between facility structures and to externally mounted electronic equipment. Additional protection requirements applicable to audio, radio frequency (RF) and other signals transmitted by coaxial, twin-axial and tri-axial cables are given in the following subparagraphs.

3.7.1 Transient levels. Electronic equipment using landlines shall be protected against the transient levels defined in Table II. The 10-by-1000 ps wave shape in Table II defines transients with a 10 ps risetime with decay to 50 percent of peak voltage in 1000 ps.

TABLE II. CONDUCTED LANDLINE TRANSIENT LEVELS

I Transient Amplitude Number of Surges 10-by-1000 ps waveform ( Lifetime )

3.7.2 Location of transient Drotcction. The location of transient protection for landlines is specified both at entrances to facilities and at entrances to electronic equipment within facilities. Depending on the type of electronic equipment and planned facility installation, combining the transient suppression specified at facility and electronic equipment entrances may be acceptable. Transient protection designs for landlines which combine the protection specified herein for installation at one location shall (1) provide high-energy suppression component(s) or device(s) connected from line to the facility earth grounding system to remove a major percentage of transient energy from each line, (2) provide low-energy suppression components connected from line to electronic equipment case ground to reduce transient energy and voltages to safe levels below the electronic equipment susceptibility level for each line, (3) be located at the entrance to the facility, and (4) have FAA approval prior to implementation.

3.7.3 Protection desian. Detailed analysis of the characteristics of suppression components and electronic equipment circuits is required to select

.r

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FAA-STD-020 REV 8 = 7003329 0009389 O T 3

-7- FAA-STD-O2Ob May 11, 1992 component parameters and design suppression circuits that will function properly without adversely affecting signals and information transmitted by individual landlines. Typical configurations for protection of electronic equipment from conducted landline transients are illustrated in FAA-STD-019, Figure 1, "Typical Configurations for Protection for Electronic Equipment from Conducted Landline Transients." Design requirements for the selection of components fo r landline transient suppression are as follows:

(a) Unipolar or bipolar suppression components shall be selected and instal-led in the proper direction for signals and voltages that are always positive, always negative, or both positive and negative relative to reference ground.

(b) The maximum landline length f o r all signals shall be expressed with the transient suppression components requited by para. 3.7 installed at each end.

(c) Protection components at facility entrances (varistor in the illustrated configurations) shall be coordinated with the protection at electronic equipment entrances to clamp or limit transients below electronic equipment susceptibility levels.

(d) Resistor R1, shall only be used to limit the transient current conducted by the suppression component at electronic equipment entrances when the conductor does not do so. The resistance of R1, shall be of sufficient value to ensure that the transient voltage at the facility entrance will turn on the facility entrance suppressor before the rated current level of the electronic equipment entrance suppressor is exceeded.

(e) The electronic equipment entrance suppressor, varistor or SAS, shall be selected to clamp and limit the transient voltage and energy safely below the equipment circuit susceptibility levels.

(f) adequately limit the transient voltage to electronic equipment circuits, a properly sized resistor, R2, is required to further reduce transient voltages.

(9 ) Capacitor C1 shall be selected in conjunction with the necessary or desired value of R2 to attenuate high frequency transient energy.

3.7.4 Functional reuuirements. The combined operating characteristics for landline transient suppression at facility and electronic equipment entrances, and requirements for individual devices shall be as follows:

(a) Reverse standoff voltaae. The operating or reverse standoff voltage rating of the suppression component shall be 20 * 5 percent above normal line voltage or the next higher voltage device available.

(b) Turnon voltacre.

electronic equipment shall be as close to reverse standoff voltage as possible using state-of-the-art devices, and shall not exceed 125 percent of reverse standoff voltage.

(c) Overshoot voltaue. Overshoot voltage shall be low enough to preclude electronic equipment damage or operational upset. The requirement shall apply for transients with rise times as fast as 5,OOOV/ps.

When the lowest voltage device available (such as an SAS) will not

Turnon voltage of the suppression component at the

(d) Clamr, (discharue) voltaae. Clamp voltage shall be below the electronic equipment susceptibility levels while dissipating the transients listed in Table 11.

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FAA-STD-020 R E V B

Hay 11, 1992

W 9003329 0009390 815

-0-

(e) Operatina lif e. The transient suppression shall be capable of safely dissipating the transients defined in Table II.

change more than 10 percent over the operating life.

(f) self-restorina capabilitv. The transient suppression shall automatically restore to the off state when the transient voltage level drops below turnon voltage for the suppressors.

3.7.5 Installation at facilitv entrance. High energy transient suppression components shall be provided in an enclosed metal junction box immediately after building or shelter entrance.

box provided by others, a separate junction box shall be provide for installation of suppression components. A ground bus bar, electrically isolated from the enclosure, shall be provided in the junction box to serve as an earth ground for the high energy transient suppressor. The ground bus bar shall be directly connected to the earth electrode system with an insulated No. 4 AWG stranded copper wire of minimum length and no loops, sharp bends or kinks. The wire insulation shall be 600 volts minimum color coded green with a red tracer. An approved connector shall be used to bond the wire to the ground bus bar. The bonding connection to the earth electrode system shall be an exothermic weld or an FAA approved pressure connection. The ground bus bar location shall permit a short, direct connection to transient suppressors.

The installation shall provide easy access to component terminals for visual inspection, test, and replacement. Each suppression device shall be replaceable, or as a minimum, the suppressor and resistor for each line shall be replaceable as a unit.

3.7.6 Installation at the electronic eauiment. Low-energy suppression components installed at the electronic equipment shall be an integral part of the electronic equipment design, or mounted in an adjacent separate metal enclosure. Bulkhead mounted, feedthrough capacitors shall be used as necessary to prevent high frequency transient energy from coupling to electronic equipment circuits. Component leads shall be of minimum length with no loops, sharp bends or kinks. Suppression component grounds shall be connected directly to the metal enclosure. The enclosure shall be directly bonded to the electronic equipment case (electronic multipoint ground.)

Access shall be provided for visual inspection and replacement of components.

3.7.7 Externallv mounted esuiment. When landlines are directly connected to electronic equipment mounted on the exterior of a facility (or which constitutes the facility), landline suppression specified in this document for facility and electronic equipment entrances shall be provided at the equipment entrance. This combined protection shall provide separate high and low energy components and grounding paths. The high energy suppression component shall be grounded directly to the earth electrode system. This connection shall be accomplished with a minimum #4 AWG insulated copper conductor. This conductor shall be color coded green with a red stripe. The low energy suppression component shall be grounded to the reference ground used by the circuit to which the landline is connected, or to the multipoint ground system. If the connection is made to the multipoint ground system, external to the equipent chassis, it shall use a 56 AWG insulated copper conductor color coded green with an orange stripe. The grounding conducting conductors for the high and low energy components shall be of minimum length and routed to avoid sharp bends, kinks or loops. Access shall be provided for visual inspection of these suppressors and for their replacement.

3.7.8 Axial landlines. Transient protection for electronic equipment using coaxial, tri-axial, and twin-axial landlines (axial-type lines) shall be provided both at facility entrances and at the electronic equipment.

Transient suppression shall be provided equally for each conductor and for

Clamp voltage shall not

When landlines terminate at a junction

Not for Resale, 07/13/2006 12:10:36 MDTNo reproduction or networking permitted without license from IHS

FAA-STD-020 REV B m 9003329 0009393 751, m

-9- FAA- STD -0 2 Ob nay 11, 1992 each s h i e l d t h a t i s n o t grounded d i r e c t l y t o t h e e l e c t r o n i c equipment case.

The p r o t e c t i o n p rov ided for e l e c t r o n i c equipment u s i n g c o a x i a l , t r i - a x i a l and tw in -ax ia l l a n d l i n e s s h a l l comply w i t h t h e requi rements g iven i n paragraphs 3.7 th rough 3.7.7 and t h e fo l lowing a d d i t i o n a l requi rements .

3.7.8.1 p r o t e c t i o n des iun . S p e c i a l a t t e n t i o n shall be g iven t o t h e d e s i g n of t r a n s i e n t p r o t e c t i o n for axial-type l i n e s . Design may b e p a r t i c u l a r l y c r i t i c a l a t RF f r e q u e n c i e s . The fo l lowing des ign requi rements apply :

( a ) Suppress ion c i r c u i t s e h a l l be des igned u s i n g s t a t e - o f - t h e - a r t components which have minimum e f f e c t upon t h e s i g n a l s be ing t r a n s m i t t e d . The u s e of v a r i s t o r s i n series w i t h RF chokes, and low c a p a c i t a n c e SAS'S paralleled wi th selected RF chokes w i l l reduce t h e e f f e c t of suppres s ion c i r c u i t s on h i g h e r f requency s i g n a l s . Other compensating t echn iques and components s h a l l be used as necessa ry .

( b ) Packaging of suppres s ion components and c i r c u i t s s h a l l be des igned t o minimize t h e e f f e c t on t r a n s m i t t e d s i g n a l s . Feedthrough components, l e a d less components, or s h o r t d i rect l ead connec t ions wi thou t bends w i l l improve performance of t h e suppres s ion c i r c u i t and reduce s i g n a l deg rada t ion .

(c ) Analyses and tests s h a l l be performed t o assure t h a t suppres s ion components do n o t degrade s i g n a l s t o an unacceptab le deg ree or c a u s e margina l o p e r a t i o n of e l e c t r o n i c equipment.

impedance, i n s e r t i o n loss, phase d i s t o r t i o n , and v o l t a g e s t a n d i n g wave r a t i o f o r RF s i g n a l s .

( d ) When t r a n s i e n t p r o t e c t i o n as s p e c i f i e d h e r e i n cannot be provided without unacceptab le deg rada t ion of performance, a l t e r n a t i v e s s h a l l be submi t t ed i n w r i t i n g and implemented wi th approval of t h e Con t rac t ing O f f i c e r .

3.7.8.2 Metal bulkhead connector plates. A metal bulkhead connec to r p l a t e s h a l l be provided where a x i a l - t y p e c a b l e s f i r s t e n t e r a f a c i l i t y . The con-n e c t o r p l a t e s h a l l b e a minimum of 1 / 4 inch t h i c k , and s h a l l be c o n s t r u c t e d of t i n - p l a t e d copper or o t h e r m a t e r i a l compat ib le wi th t h e connec to r s . The p l a t e or p l a t e s s h a l l have t h e r e q u i r e d number and types of feed-through connec to r s t o t e r m i n a t e a l l t h e e x t e r n a l l i n e s . The connec to r s s h a l l p r o v i d e a p a t h t o ground f o r cable s h i e l d s , except when t h e s h i e l d must be i s o l a t e d fo r proper equipment o p e r a t i o n . If e x t e r n a l and i n t e r n a l c a b l e s are of d i f f e r e n t s i z e s , t h e changeover i n c a b l e sire s h a l l be accomplished by t h e feed-through connec tors a t t h e p l a t e . The connec tor p la te s h a l l be bonded t o t h e e a r t h electrode system w i t h a N o . 2 / 0 AWG copper cable color coded g reen w i t h a red tracer. A d d i t i o n a l l y , when b u i l d i n g steel is p r o p e r l y bonded t o t h e e a r t h e l e c t r o d e system, t h e bulkhead connec tor p l a t e s h a l l be connected t o b u i l d i n g steel. Exothermic welds or e q u i v a l e n t s h a l l be used f o r t h e s e connec t ions .

3.7.8.3 I n s t a l l a t i o n a t f a c i l i t y e n t r a n c e s . T r a n s i e n t s u p p r e s s i o n components for a x i a l - t y p e c a b l e s s h a l l be packaged i n a sealed metal e n c l o s u r e w i t h a p p r o p r i a t e connectors a t each end t o permit i n - l i n e i n s t a l l a t i o n a t t h e connec tor plate. The ground connec t ion f o r v a r i s t o r s or o t h e r s u p p r e s s i o n d e v i c e s used a t f a c i l i t y e n t r a n c e s , b u t n o t mounted a t t h e bulkhead p l a t e , s h a l l be i s o l a t e d from t h e suppres s ion c i r c u i t enc losu re .

l e a d s h a l l be brought o u t of each suppres s ion c i r c u i t e n c l o s u r e and connected t o an a d j a c e n t bus or t i e po in t . The ground bus s h a l l be i s o l a t e d from t h e connec tor p la te and i t s enc losu re , and connected d i r e c t l y t o t h e f a c i l i t y e a r t h electrode system wi th a n i n s u l a t e d (g reen w i t h a red tracer) No. 4 AWG s t r anded copper w i r e . T h i s grounding conductor s h a l l be s e p a r a t e from t h e grounding conductor mentioned i n pa ra . 3.7.8.2. All ground l e a d s and w i r e sha l l be as s h o r t as possible wi th no loops , s h a r p bends or k inks . Bonding t o

P a r t i c u l a r a t t e n t i o n s h a l l be g i v e n t o t h e

A n i n s u l a t e d ground

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FAA-STD-020 REV B = 9003329 0009392 698

May 11, 1992

-10-the ground bus shall be by FAA approved connectors and to the facility earth electrode system by exothermic welds or equivalent.

3.7.8.4 Installation at electronic e m i m ent entrances. Off-the-shelf suppression components shall be provided as an integral part of electronic equipment design as specified herein for other types of landlines. When electronic equipment without transient suppression is required for the facility, electronic equipment suppression components shall be packaged in a separate enclosure with connectors on each end for in-line connection directly to the equipment. When isolation of the cable shield and connector body is required for electronic equipment operation, suppression component grounds shall be isolated from the component housing and connected directly to the electronic equipment case which is connected to the earth ground structure.

All electronic equipment entrances aha11 be located in a common area, close to the case ground to minimize circulating ground currents on the case.

3.7.9 fiber oDtics cable. This standard does not preclude the use of fiber optics cable as a substitute for metallic signal, control and data cables.

Where fiber optics cable uses conductive armor, it shall be terminated to the multipoint ground system at the facility entrance. If the cable is internal to the facility, conductive a m o r shall be terminated to the multipoint ground system at the equipment entrance. The use of fiber optics cable without a conductive shield or armor is permitted.

3.0 Groundinu reuuirements.

3.0.1 General. The grounding of electronic circuits and equipment shall be accomplished to minimize interference levels and hazards to personnel. The facility ground system will be provided in accordance with FAA-STD-019.

3.0.2 Etminment remirinu -electronic sinale arounds. Where electronic equipment performance dictates an isolated electronic single-point ground system for proper operation, all the equipment and its installation shall comply with the following:

3.8.2.1 Electronic sinale-mint around svstem . The single-point ground system or plane shall be isolated from the electronic equipment case. If a metal chassis is used as the electronic single-point ground, the chassis shall be floated relative to the case. Design practices shall be such that the single-point ground of the electronic equipment can be properly interfaced with other electronic equipment without compromising the system. If neces-sary, this single-point ground system may be filtered for high frequencies.

3.8.2.2 Input and output sianals. The "high" and "low" sides of input and output signals shall be isolated from the electronic equipment case and balanced with respect to the signal reference. Operating and adjusting controls, readouts or indicating devices, protective devices, monitoring jacks and signal connectors shall be designed to isolate both the high and low side of the signal from the case.

3.8.2.3 Electronic sinale-mint around tenninalfs). insulated single-point ground system terminal(s) shall be provided on each electronic equipment case where an isolated signal reference is required. The single-point ground reference for the internal circuits shall be connected to this terminal. This terminal(s) shall be used to terminate cable shields, and to connect the isolated signal ground of the electronic equipment to the aingle-point ground system in the facility. A connector pin, a screw or pin on a terminal strip, an insulated stud, jack or feedthrough, or an insulated wire shall be an acceptable terminal when it conforms to the following:

L.

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FAA-STD-020 R E V B 9003329 0009393 524

-11- FAA-STD-020b May 11, 1992

(a) Each terminal shall be clearly marked, labeled, or coded in a manner that does not interfere with its intended function. These marks, codes, or labels shall be permanently affixed and shall utilize green with yellow stripes.

Wire insulation shall be green with a yellow tracer.

(b) Insulated stranded wires shall not be less than No. 12 AWG copper with a length, outside the case, of not less than 1 foot nor greater than 3 feet.

3.8.2.4 Isolation. With all external power, signal and control lines disconnected from the electronic equipment, isolation between the single-point ground system terminals and the case shall not be less than 10 megohms.

3.8.2.5 Electronic sianal lines and cables. Electronic signal lines shall be twisted shielded pairs with the shield insulated. Cables consisting of multiple twisted pairs shall have the individual shields isolated from each other. Cables with an overall shield shall have the shield insulated.

3.8.2.6 Termination of individual shields. Shields of pairs of conductors and the shield of cables containing pairs without individual shields shall be terminated in accordance with the following:

(a) The length of unshielded conductors shall not exceed 1 inch. To meet this requirement, the length of shield pigtail may be longer than 1 inch if necessary to reach ground, but shall be kept to a minimum.

(b) Shields terminated outside the electronic equipment shall employ minimum length pigtails between the breakout of the shield and the connection to the bonding halo or ferrule ring, and between the halo or ferrule ring and the shield pin on the connector. The unshielded length of a signal line, outside the electronic equipment case shall not exceed 1 inch with not more than 112 inch exposed length as the desired goal.

(c) Shields, individually and collectively, shall be isolated from overall shields of cables bundles and from electronic equipment cases, racks, cabinets, junction boxes, conduit, cable trays, and elements of the electronic multipoint ground system. Except for one interconnection, individual shields shall be isolated from each other. Care shall be exercised to assure this isolation is maintained in junction boxes, patch panels, and distribution boxes throughout the cable run.

interrupted, such as in a junction box, the shield shall be carried through.

The length of unshielded conductors shall not exceed 1 inch.

requirement the length of shield pigtail may be longer than 1 inch if necessary where grounded, but shall be kept to a minimum.

(d) Circuits and chassis shall be designed to minimize the distance from the connector or terminal strip to the point of attachment of the shield grounding conductor to the electronic signal reference. The size of the wire used to extend the shield to the circuit reference shall be as large as practical but shall not be less than No.16 AWG or the maximum wire size that will fit the connector pin. The use of a common shield ground wire for input and output signals, for both high level and low level signals, for signal lines and powerlines, or for electronic signal lines and control lines shall be avoided.

(e) through the connector or past the terminal strip to individual circuits or chassis if required to minimize unwanted coupling inside the electronic equipment.

bundle shields grounded in accordance with para. 3.8.2.7 shall be provided.

When an electronic signal line is

To meet this

Nothing in this requirement ahall preclude the extension of the shields

Where extensions of this type are necessary, overall cable or

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FAA-STD-020 REV B 9003327 0009394 460 =

May Il, 1992

-12-

3.8.2.7 Termina t ion of o v e r a l l s h i e l d s . C a b l e s t h a t have an o v e r a l l s h i e l d ove r i n d i v i d u a l l y s h i e l d e d p a i r s s h a l l have t h e o v e r a l l s h i e l d grounded t o t h e case a t each end and a t i n t e r m e d i a t e p o i n t s i n accordance w i t h t h e fo l lowing:

( a ) S h i e l d s of cables t e rmina ted i n connec to r s s h a l l be bonded t o t h e connec tor s h e l l as shown i n FAA-STD-019, F i g u r e 6 , "Grounding of Overall Cable S h i e l d s t o Connectors and Penetrated Walls," a ) "Box Connector" o r b ) "Grounding of Mult i -pin Connector." The s h i e l d s h a l l be c a r e f u l l y c leaned t o remove d i r t , m o i s t u r e , and c o r r o s i o n p roduc t s . The s e c u r i n g clamp of t h e connec tor s h a l l b e c a r e f u l l y t i g h t e n e d t o a s s u r e t h a t a l o w r e s i s t a n c e bond t o t h e connec to r s h e l l is achieved comple te ly around t h e c i r cumfe rence of t h e cable s h i e l d . The bond s h a l l be p r o t e c t e d a g a i n s t c o r r o s i o n i n accordance wi th pa rag raphs 3.9.5 and 3.9.5.1. The panel-mounted part of t h e connec tor s h a l l be bonded t o t h e mounting s u r f a c e i n accordance w i t h para. 3.9.8.

( b ) Cables which p e n e t r a t e w a l l s or panels o f cases or e n c l o s u r e s wi thou t t h e u s e of c o n n e c t o r s s h a l l have t h e i r s h i e l d s bonded t o t h e p e n e t r a t e d s u r f a c e as shown i n FAA-STD-019, F igu re 6, c ) " P a r t i t i o n P e n e t r a t i o n . "

( c ) Grounding of o v e r a l l s h i e l d s t o t e r m i n a l strips s h a l l be as shown i n FAA-STD-019, F i g u r e 7 , "Grounding O v e r a l l S h i e l d t o T e m i n a l S t r ip ."

( d ) Where t h e c a b l e c o n t i n u i t y is i n t e r r u p t e d such as i n a j u n c t i o n box, t h e s h i e l d s h a l l be carried through and grounded a t t h e equipment box. The l e n g t h of unsh ie lded conduc to r s s h a l l no t exceed 1 inch . To meet t h i s requi rement t h e l e n g t h of s h i e l d p i g t a i l may b e l o n g e r t h a n 1 i n c h i f necessa ry t o r each t h e equipment ground, b u t s h a l l be k e p t t o a minimum.

(e) The s h i e l d s of t h e i n d i v i d u a l p a i r s s h a l l be grounded as s p e c i f i e d i n para . 3.8.2.6.

3.8.2.8 S i n a l e - p o i n t aroundina of e l e c t r o n i c e a u i m e n t . Each s i n g l e - p o i n t ground t e r m i n a l s h a l l be connected t o t h e f a c i l i t y s i n g l e - p o i n t ground system i n accordance w i t h t h e fol lowing:

( a ) t h e i r l o c a t i o n or f u n c t i o n cannot or should n o t be mounted w i t h o t h e r e l e c t r o n i c equipment, s h a l l have an i n s u l a t e d copper cable i n s t a l l e d between t h e e l e c t r o n i c s i n g l e - p o i n t ground t e r m i n a l s p e c i f i e d i n 3.8.2.3 and t h e n e a r e s t e l e c t r o n i c s i n g l e - p o i n t ground system ground p l a t e as i l l u s t r a t e d i n F igu re 2, "S ing le P o i n t Grounding f o r a n I n d i v i d u a l Uni t o r P i e c e o f E l e c t r o n i c Equipment." Th i s cable s h a l l have a c r o s s - s e c t i o n a l area of 500 c i r c u l a r m i l s per l i n e a r f o o t .

( b ) t o g e t h e r i n a r a c k or c a b i n e t , a s ing le-ground bus b a r s h a l l be i n s t a l l e d as shown i n F i g u r e 3, " S i n g l e Po in t E l e c t r o n i c S i g n a l ground Bus B a r I n s t a l l a t i o n i n Rack or Cabine t . " The bus b a r s h a l l b e copper and s h a l l p r o v i d e a minimum c r o s s - s e c t i o n a l area of 125,000 s q u a r e m i l s . The bus bar s h a l l be d r i l l ed and tapped f o r No. 10 m c r e w s .

r e l a t i v e l o c a t i o n of t h e i s o l a t e d e l e c t r o n i c s i n g l e - p o i n t grounding te rmina ls on t h e e l e c t r o n i c equipment.

s u p p o r t s t h a t p r o v i d e a t least 10 megohms DC resistance between t h e bus b a r and t h e r a c k or c a b i n e t .

I n d i v i d u a l u n i t s or pieces of e l e c t r o n i c equipment which by n a t u r e of

Where t w o or more u n i t s or p i e c e s of e l e c t r o n i c equipment are mounted

The h o l e s s h a l l be located as r e q u i r e d by t h e

The bus bar s h a l l be mounted on i n s u l a t i n g

( c ) Each e l e c t r o n i c equipment isolated s i n g l e - p o i n t ground terminal s h a l l be i n t e r c o n n e c t e d t o t h e bus bar by means o f a s o l i d or f l e x i b l e t i n n e d copper jumper of s u f f i c i e n t c r o s s - s e c t i o n a l area so t h a t i ts resistance is 5 m i l l i o h m s or less (No.12 AWG minimum.) The jumper s h a l l b e i n s u l a t e d or mounted i n a manner t h a t main ta ins t h e r e q u i r e d degree of i s o l a t i o n between

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FAA-STD-020 REV B 9003329 0009395 3T7

-13- FAA-STD-O2Ob May 11, 1992

I N D I V I D U A L U N I T OR P I E C E

OF ELECTRONIC EQUIPMENT

C I R C U I T BOARD OR

FLOATING CHASSIS

BOND CENTER TAP TO

OR FLOATING CHASSIS

TO RECTIFI PC BOARD SIGNAL GROUND

TO F A C I L I T Y ELECTRONIC

FEEDER GROUND PLATE

TERMINAL ISOLATED FROM

CASE O R CABINET

EQUIPMENT GROUNDING CONDUCTOR CONNECTED

TO TRANSFORMER CASE AND CABINET

I L A C POWERLINE

I

L T O M U L T I P O I N T GROUND SYSTEM

Figure 2. S i n g l e P o i n t Grounding f o r I n d i v…