A NEW WAYTO LOOK AT SYSTEM GROUNDING

EDWARD 0. MINOR

FUNCTIONAL LINE DIAGRAM GROUPAero-Space Division

The Boeing CompanySeattle, Washington

SUMMARY

The reports of destructive grounding system faultcurrents and abortive interference are costlypages in the annals of electro-technology.

The complexity of their resolution is compoundedbecause the design intelligence is not readilyapparent in the tangle of architectural, struc-tural, and electrical schematic diagrams withwhich the grounding system is described.

Through the development of a unified set of func-tional diagrams which present a precise graphicimage of the total grounding system entity a meanshas been provided to efficiently establish theexact equipment configuration employed and to dis-play the grounding as an integral aspect of thepower and signal functions.

The drawings depict in detail the electrical con-tinuity between earth grounds, conductive struc-tures, and electrical returns.

The drawing format features an arrangement of dataon the drawings to illustrate the logical sequencein the establishment and distribution of theground reference potential.

The objective of the method of presentation is toillustrate grounding as a sequence of subsystems,defined in distinct levels of indenture. Eachlevel of indenture consists of a similar group ofdrawings in which each major subdivislon is indi-vidually brought into focus and enlarged to revealgreater detail.

The improved capability for analysis and monitoringof the entire grounding system increases theassurance of determining the optimum low impedancedesign, implementation consistent with design ob-jectives, and resolution of faults related to thegrounding.

PROLOGUE

The grounding is the simplest aspect of a complexel-ectrical-electronic system from the design view-point.

The quantitative analysis is straight forward, andthe hardware decisions necessary to achieve therequired impedance objectives are clearly evident.

And still, more faults in power and signal systemsarise from grounding problems than from any otherindividual cause.

The fundamental reason for this paradox is thatsystem design is not adequately expressed by themaze of drawings and documents currently utilizedto describe grounding.

As a result, communication of the design intelli-gence is retarded, leaving gross parameters def in-ing implementation, and providing only cumbersomemethods for monitor and control.

Since every item of equipment contains a portionof the grounding system, the extens'ive scope ofthe comnon impedance involved makes evaluation ofthe completed system a major task. The commonimpedance provides an optimum medium for the pro-pagation of electrical interference; and a ground-ing fault in any item directly affects virtuallyevery other aspect of the system.

When a problem occurs, literally hundreds of draw-ings must be examined to determine the most rudi-mentary details of Earth Grounds, StructuralGrounds, Electrical Grounds, Power Commons,Shielding termination and bonding of mating sur-faces.

In addition, the grounding information which iscontained in conventional diagrams is cumbersometo use for analysis. Data must be abstracted fromnumerous drawings and documents, and translatedinto a format which expresses the electricalsignificance of the design.

The manpower expended on reference researchassumes staggering dimensions because the samebasic steps must be repeated with each individualeffort to look into the grounding system. A lowyield of reusable information occurs simply be-cause there ordinarily is no means to record thedata in a systematic manner that expedites anefficient recovery to meet a subsequent require-ment.

An efficient means of representing the groundingsystem from preliminary design configurationthrough assembly and test completion can obviatecostly duplication of effort and redesign by pro-viding assurance of adequate developmental monitorand control.

SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC: SYSTEMS VOL. AES-2, NO. 4 JULY, 1966754

A DATA RECOVERY TECHNIQUEFOR THE GROUNDING SYSTEM

Data RECOVERY is the key element required to pro-vide a means for efficient communication of thesystem concept. The essential objectives are torecord, organize, and effectively relay all per-tinent details of how the system is fabricatedand how it works.

A suitable Data Recovery Technique for the ground-ing system defines every component utilized with afocus of emphasis on the fundamental distributionof electrical continuity between components andthe system function of each segment or aspect.

A Data Recovery Technique consisting of analyti-cal diagrams which display the distribution ofgrounding as a sequence can provide a means toassure efficient communication of the systemintelligence during all phases of development andutilization.

The content and format for a comprehensive folioof grounding reference system diagrams are out-lined in the following criteria and sample draw-ings.

The drawings described are arranged to accelerateinitial comprehension through a physical, spatialrepresentation of the grounding of the geograph-ical site, the Facility enclosures, the equipmentinstallation, and subassemblies within equipment.

The following general considerations are observedin all the drawings to facilitate efficientassimilation of the information presented:

1. System orientation of layout.2. Emphasis of more important design aspects.3. Elimination of congestion of detail.4. Grouping of related data into logical

concentrations.5. Arrangement to minimize crossing and bend-

ing of lines.

Indenture

A Method of indenture is developed to correspondwith the '.uildup of equipment from components.Distinct levels of drawing.scope are establishedto illustrate circuit cards, major subassembliessuch as drawers, and end item equipment such asracks or consoles. Specific levels of system dia-grams display the integration of eouipment intothe facility, the facility installation, and thecabling between related facility sites.

Abstract ion

Abstraction is employed as a means of presenta-tion. The essential information of grounding isabstracted from the numerous general sources andconsolidated into a single set of data. Thedrawings depict grounding as a sequence in whichdistrioution of a fundamental reference potentialis accomplished throughout a system of conductivestructures and an isolated electrical returnsystem.

Division of the total grounding entity intoStructures, Electrical Returns, and Earth Groundaffords optimum flexibility in the development ofanalytical techniques of presentation consistentwith the design objectives of each aspect of thesystem.

Description of the Facility Example

The facility shown is hypothetical; typical of ahardened and dispersed operational or test site.A "star" single-point configuration of groundingsystem is illustrated.

A radial counterpoise is utilized to establishEarth Ground as the reference potential. Distri-bution is provided through a Facility Ground TiePoint (FGTP) to the conductive structures (Struc-tural Ground) and the electrical return system(Electrical Ground) .

The Control Building is assumed to be a steel en-closure; equipment is installed on a shock mount-ed floor grounded to the FGTP by flexible straps.

Cabling between equipment is generally enclosed byan overall shielding braid, grounded through theconnector backshell to equipment chassis at eachend.

All shielding for RF interference is terminated toa ground source at both ends. Shielding for AFinterference is terminated to a ground at thesource and isolated at the load end.

Low impedance continuity is provided to an other-wise isolated electrical ground bus. The Electri-cal Grounding is a single line distributionbranching out into every item of equipment definedto the level of the individual components on cir-cuit cards.

FIGURE 1: FACILITY LAYOUT DIAGRAM

Figure 1 exemplifies the highest level of inden-ture. The drawing is pictorial in format andemphasizes details of the installation of EarthGround.

The geographical orientation of the Facility lay-out diagram provides a gross familiarization ofthe area, the counterpoise configuration, generalrelative position of buildings, and routing ofcable runs between major items within the Facility.Scaling of the drawing is useful for estimatinglengths of cabling out to length at the time ofinstallation, and relative proximity of majoritems.

Continuity of presentation is provided throughutilization of cutaway views of the externalstructure, providing an insight into the secondlevel of indenture.

SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-2, NO. 4 JULY, 1966 755

FIGURE 2: CONTROL BUILDING STRUCTURE

The second level of indenture depicts the physicalappearance of the Control Building, its contentsand the means employed to distribute the EarthGround from the Facility Ground Tie Point toequipment through structure ground and the elec-trical returns.

The pictorial format is utilized to maintain ahigh degree of continuity in the presentation asthe scope of the drawing is decreased, bringinginto focus the most important items enlarged toreveal increased detail.

Significant items illustrated:

Facility Ground Tie Point

Structural Ground components:

Steel enclosureShock mounted floorTypical equipment installation

Electrical Ground components:

Electrical ground busCable to equipment

FIGURE 3s EQUIPMENT STRUCTURE

Figure 3 illustrates typical implementation withinthe individual item of equipment. Distribution ofstructure ground is accomplished through bondedmembers of the rack structure. Direct physicalcontinuity to the drawer structural chassis isprovided through low impedance connectors.

Electrical ground enters the rack by cable, fromthe Electrical Ground Bus, and continuity is pro-vided to an internal rack bus by a low impedancestrap or wire comparable to that of the cable.Each drawer is equipped with a bus bar directlycoupled to the rack bus by low impedance connect-ors. Distribution to each subassemoly within thedrawer is provided by a separate wire from thedrawer bus.

Since the implementation indicated is typical forevery drawer, only one has been shown, and an add-itional level of indenture has not been used todisplay the particular details within each drawer.

FIGURE 4: SHIELDING AND EQUIPMENT GROUNDING

Configuration and termination of shielding is com-bined with structural grounding on drawings simi-lar in format to wiring diagrams.

The Facility level diagram identifies all cablingbetween equipment and specif'ies the structureground provided for each individual rack, tabinet,or console.

A general physical orientation is indicated bydelineation of major areas on the drawings.

Equipment is shown in outline form, with a struc-ture ground symbol affixed to denote the specifiedmeans of providing continuity from the equipmentchassis to facility structures.

At this level of indenture, the cable is represen-ted by a single line symbol, with suitable anno-tation to indicate termination of the overallouter shielding which encloses all wires of thecable.

The drawing is arranged to display the parallel-ism of continuity between overall shieldinggrounded to chassis at both ends.

Illustration of all related equipment and cablingon a single diagram also provides visibility forevaluation of multiple-point grounding of elec-trical returns and fault current distributionthrough structures.

FIGURE 5: INTER-EQUIPMENT CABLING DETAIL

Details of shielding of individual wires of theinter-equipment cables are given on a subsequentlevel of indenture, with the equipment designatedshown as a distinct subsystem. The equipment unitis represented by an outline near the center cfthe drawing and all connectors for inter-equipmentcabling are shown around the periphery of the unitoutline.

References identify terminations which providecontinuity for grounding of shields within theequipment. Suitable notation is used to distin-guish between electrical or structural groundingtermination of shields.

Identification of signal nomenclature may be in-cluded on this drawing, to provide a convenientreference for system analysis.

FIGURE 6: EQUIPMENT INTRA CONNECTION

Shielding configuration and the termination of allgrounding wires within equipment is illustrated indrawings identical in format to the FacilityShielding and Equipment Grounding diagram, Figure4.

In the first level of indenture within equipment(Figure 6A), the equipment unit is represented asan outline, with major subassemblies such asdrawers identified. All connectors for inter-equipment cabling are shown and all internal wir-ing from each connector is given. All connectionsto drawers are drawn with a minimum of crossedlines by illustrating the drawer connectors inseparated segments where required.

The second level of indenture (Figure 6B) consistsof drawings in which the drawer is the outer peri-phery of scope and minor subassemblies such ascircuit cards are shown in block outline form.

References are included to denote points of con-tinuity to Electrical Ground and Structural Groundat each level.

SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-2, NO. 4 JULY, 1966756

FIGURE 7: FACILITY GROUNDING SYSTEM

Figure 7 is a functional block diagram of theelectrical continuity between the major componentsof the grounding system of the Facility. Theelectrical significance of each item is stressedand the physical orientation is less evident.

The counterpoise is represented by the EarthGround symbol, conductive metal enclosures areoutlined, and principal distribution paths areemphasized by use of heavy lines.

Typical equipment installation is indicated, andreferences i-dentify cables from the electricalground bus to equipment. The means by which Str-ucture Ground and Electrical Ground is supplied tothe remote locations in the Test Building is shxwn.

FIGURE 8: FACILITY ELECTRICAL GROUNDING

The power and return system described is represen-tative of an installation using commercial 60cycle AC, with a standby diesel generator, and abattery set for emergency use.

The primary source, the standby source, the emer-gency source, and their respective loads in theControl Building and the Test Building are indi-cated.

A Power Distribution Block Diagram (Figure 8A)precedes the Return Distribution, and identifiesthe power sources, distribution functions, and therespective equipment loads. Power distribution isdisplayed as a sequence originating at the powersource located at the left in the drawing; andproceding from left to right through the distribu-tion functions t,o the equipment loads.

The Return Distribution Diagram (Figure 8B) isarranged to reflect identically the Power Distri-bution Block Diagram, with power sources incorresponding locations to the left and relatedloads to the right.

The system orientation achieved by the FunctionalFlow format of the drawing is an aid in evaluationof multiple point grounding of returns, power dis-tribution faults, and common impedances betweenequipment.

Implementation of the Single Point Grounding con-cept is revealed, and instances in which Electri-cal Ground reference is supplied to equipmentthrough power return circuits are readily discer-nible.

FIGURE 9: EQUIPMENT ELECTRICAL GROUNDING

In the example given, (Figure 9A) the diagram de-picts the cable from the Electrical Ground Busentering the equipment at the left end of thedrawing.

Heavy lines indicate the continuity from the cableconnector to the rack Electrical Ground Bus andthe direct connecti6n to the drawer bus bars.

The equipment implementation pictured in Figure 9Ais approaching an optimum low impedance design,adequate to fulfill most grounding requirements.Example 9B is typical of undesirable practicecommonly employed.

PACKAGING

Utility of the drawings is enhanced by packagingin document form. The completed drawings areeleven inches in width and whatever length requir-ed. Pages are printed on pre-folded sheets andbound in two catagories according to indenturelevel.

The Facility diagrams comprise a system packagein which the individual end item of equipment isthe unit component. The inter-equipment cablingdetail drawings are included in the system pack-age to provide detail visibility to the equipmentlevel.

The unit is then treated as an individual sub-system. The intraconnection diagram of the rackis followed by that of each drawer. Return dis-tribution for the rack and each drawer are pack-aged together in sequence.

In this manner, the drawings of each discrete itemof equipment are postured for integration into thetotal system picture.

APPLICAT ION

Maximum continuity of information from the inter-equipment interface to the most detailed connec-tion within a circuit card is achieved by the con-tinuation of the systematic sequence of indenture.

The grounding can be traced out from the counter-poise to any component on any circuit card in anydrawer in a matter of seconds. The reverse pro-cess can be accomplished with equal ease, and thereturn circuitry from a component to one inanother unit is clearly evident.

The grounding system is defined, and the data isarranged in a manner so that it can be RECOVEREDfor immediate application in planning, systemdevelopment, assembly and test operations.

Grounding of the electrical return distributionwithin each equipment item is illustrated in asimilar manner, with the equipment treated as asubsystem. Where simplicity of equipment permits,the distribution within each drawer to circuitcards is illustrated on the rack drawing.

SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-2, NO. 4 JULY, 1966 757

CONCLUS IONS:

The unique format and comprehensive content of thegrounding diagrams provide an effective aid inWeapon System development and evaluation. Theinformation presented on the drawings is requiredduring system design, equipment manufacturingdevelopment, assembly and checkout, training, andpost-completion analysis efforts.

Each individual effort to determine groundinginformation must include essentially the samesteps of abstracting the required data from exist-ing architectural, structural and electricalwiring diagrams.

The grounding drawings are a convenient, efficientmeans to perform the document research once andrecord the information so that it can be recoveredeasily to support all subsequent analysis efforts.An additional benefit is accrued in that the sys-tem is subjected to detailed scrutiny by theengineering authority preparing the drawings.Grounding discrepancies detected can be resolvedat the earliest possible time with minimum ofhardware change.

The value of .the diagrams as an aid in systemanalysis is predicated upon their accurate repre-sentation of the actual circuitry of the system.

Low frequency characteristics of the groundingsystem can be derived from the drawings if theconductor composition, size, length and termina-tion are shown in sufficient detail.

Evaluation of high frequency characteristics re-quires the consideration of inductive and capaci-tative parameters of the equipment wiring. Tosupport a complete quantitative analysis, exhaus-tive data such as relative proximity of adjacentwiring, cable routing, and impedance of terminat-ing circuitry must be made available.

To this end the drawings provide a convenient out-line to which the required details can be affixed,establishing a direct correlation between thequalitative and quantitative analyses.

The information required is not available throughany other media with the systematic organizationfeatured in this set of data. The draw.ings caneliminate duplication of data research and exped-ite accomplishment of the following engineeringactivities:

PRELIMINARY DESIGN EVALUAT IONSystem implementation of grounding requirementsParallelism of continuity through structuralgrounds.Termination point of inter-equipment cablesConformance to standardsCost-effectiveness of design

ASSEMBLY AND CHECKOUTDefinition of test requirementsIsolation of system discreoanciesDevelopment of corrective change proposals

SYSTEM FAULT ANALYSISPower Distribution

Short circuits to structureShort circuits to return distribution

Signal PropagationSignal Common noiseTransient interferenceCross talk interference

Safety Analys'isHazardous current effects

Equipment overheatingInadvertant programming

Personnel hazardsElectrical shock protectionSecondary effects

ELECTRO- INTERFERENCE EVALUATIONImpedance analysisInductive and capacitive coupling analysisPreparation of E-I Test requirements

Definition of test proceduresIdentification of test pointsEvaluation of test data

RF1 FilteringSeries cascade connectionBonding to equipment chassis

Shielding discrepanciesTermination requirementsConf igurat ion

Electrical GroundingMultiple point DC groundsConductor impedance

Analysis of system design with the aid of recover-able grounding data will facilitate accomplishmentof the following objectivest

(1) Identification of optimum cost-effectivenessof grounding system design.

(2) Assurance that design objectives are accom-plished in the implementation employed.

(3) Evaluation of effects of faults and changesoccurring in power and signal systems.

(4) Definition of Electro-Interference tests,determination of test points and evaluationof results.

(5) Monitor of design evolution to avoid problemrepetition in subsequent similar developments,

SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-2, NO. 4 JULY, 1966758

FIGURE 1

FACILITY LAYOUT DIAGRAM

DEPICTS EARTH GROUND ANDGEOGRAPHICAL LAYOUT

(O) CONTROL BUILDING BUNKER.© CONTROL BUILDING.

(3 REMOTE TEST BUNKER & BLDG.® COUNTERPOISE.@( UNDERGROUND FUEL TANK.

FIGURE 2

CONTROL BUILDING STRUCTURE

ILLUSTRATES STRUCTURAL CONFIGURATIONOF PRINCIPAL GROUNDING COMPONENTS

o FACILITY GROUND TIE POINTS.

® SOLID COPPER STRAP

® CONTROL BUILDING ONELECTRICAL GROUND BUS.

®GROUND CABLE TO EQUIPMENT.

(5 TYPICAL EQUIPMENT INSTALLATION.

@© SHOCK MOUNTED FLOOR.

2 FLEXIBLE BRAIDED STRAP

® CABLES TO TEST BUILDING

I SOLID COPPER STRAPFROM COUNTERPOISE.

FIGURE 3

EQUIPMENT STRUCTURE

PORTRAYS THE IMPLEMENTATION OF ELECTRICAL ANDSTRUCTURAL (CHASSIS) GROUNDING WITHIN EQUIPMENT UNIT.

OGRoUND CABLE FROM CONTROL BUILDINGELECTRICAL GROUND BUS.

CZEQUIPMENT UNITELECTRICAL GROUND BUS.

(I DRAWERELECTRICAL GROUND BUS.

@IEQUIPMENT STRUCTURE.(CHASSIS)

©CHASSIS BONDING STRAP

(BRAIDED STRAP TOSHOCK MOUNTED FLOOR.

0DRAWER CHASSIS.5WIRE FROM DRAWERELECTRICAL GROUND BUSTO CIRCUIT CARDS.

759SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-2, NO. 4 JULY, 1966

CONTROL BUILDING OUTLINE

(2) EQUIPMENT UNIT OUTLINE

INTER- EQUIPMENT CABLE

(1) EQUIPMENT UNIT OUTLINE

SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-2, NO. 4 JULY, 1966760

FIGURE 7FACILITY GROUNDINGSYSTEM

1 CONTROL BUILDING ELECTRICAL GROUND BUS.

2 EQUIPMENT UNIT ELECTRICAL GROUND BUS.

3 EQUIPMENT UNtT CHASStS GRO-UND.

/ SHOCK MOUNTED FLOOR.

FIGURE 8FACILITY ELECTRICAL GROUNDING

CONTROL BUILDING

FIGURE 8APOWERFLOW

FIGURE 8BRETURNFLOWANDGROUNDING

PRIMARY A C POWER SOURCE.

(2) STANDBY A C POWER SOURCE.

(3 A C POWER DISTRIBUTION BOX.

CONTROL BUILDING AC POWER LOADS.

s BATTERY CHARGER.

( BATTERY SET.

O )DC POWER DISTRIBUTION BOX.

(a) CONTROL BUILDING DC POWER LOADS.

(9 FACILITY GROUND TIE POINT.

( TEST BUILDING ELECTRICAL GROUND.

(3 TEST BUILDING A C LOADS.

TEST BUILDING D C LOADS.

EQUIPMENT UNIT OUTLINE

DRAWER OUTLINE

a DRAWER SUBASSEMBLY

FIGURE9B

SUPPLEMENT TO IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-2, NO. 4 JULY, 1966

TEST

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