A Consensus on Powering and Grounding 

Sensitive Electronic Equipment

Thomas S. Key

Sandia National Laboratories

Albuquerque NM

François D. Martzloff

National Bureau of Standards

Gaithersburg MD

Reprinted, with permission, from Conference Record, IEEE IAS Annual Meeting, October 1986

Significance:

Part 6 – Textbooks, tutorials, and reviews

A paper presented to the IEEE Industry Applications Society Annual Meeting to support a proposal for

developing a new standard in the Color Book series, “Powering and Grounding Sensitive Electronic

Equipment,” Standards Project P1100. 

The effort was successful and an active Working was launched. The initial goal was to complete the

project in four years. Unfortunately, the issues were sufficiently complex and opinions diverse to the poin

that the final “Emerald Book” IEEE StdTM 1100 was not completed until 1992, still a reasonable gestation

period by comparison to some other IEEE projects.

One of the lingering issues was to clearly define “sensitive electronics.” That ambiguity was resolved in

the 1999 update by dropping out the qualifier “sensitive.” It is also interesting to note that the 1999 updat

of the existing 1992 book took seven years, compared to the six years it took to start from the vision (a

glimmer) described in this paper.
A CONSENSUS ON POWERING AND GROUNDING SENSITIVE ELECTRONIC EQUIPMENT 

Thomas S. Key, Member IEEE 

Sandia National Laboratories 

Albuquerque, NM 87185 

Abstract-Aseensitiveileebariepmoessing systems 

proliferate in our facilities so do power-related 

pr&bms. Efforts to alleviate these problems have 

ranged fixm installing expensive power conditioning 

~-~app1rinsspedalgrauding~n~ 

faund in mwtirral safe grwndhg practtoe Understanding & what is actudlly going on has been lack- 

%. We find eMmate power systems, modified from 

basic practice to the extent of being unsafe, that 

amtinue to be plagued with parering- and groundingrelated prcblems. Out af this chaos we are persuaded 

to study Md understand the complexities of the pmblem and to beain devela,inS mod practices. This is 

the drjective d;r the IEE~ w&.&hg -~roup on Powering 

and Grcunding Sensitive FJ.dmnic Equipment, Standards Project PUOO. we will intmduci project p1100, 

preview its scope and technical content and, most 

hportantly, idte participation in this seriously 

needed consensus standard activity. 

INTRODUCTION 

Powering and gmmdhg sensitive electronic equipment 

is a growing concern for commercial and industrial 

power system designers. ThYs concern frequently 

matenalhes after start-up when electronic system 

 begin^-* ""pinsf=~ow=- cadittning~mentormagicgmundYlgmethcdsisa 

OlmmanrPspanse. fnrwma~tbiscarrsehasledto 

unsafe pr- and vhlatk~ns of the Nationdl Electrical Code withAlt solving operating problems. hlthmgh gmd teddcd information is available, there 

is presently no consensus on recommended practice. 

~leawsraspcnsibkPnglneerstoproceedfrormvhat 

the~~~ovcrrcanreadil~ obtain intheliteratuie. ~lfozbnatdy, them 5s &nnicting information 

in the Uterature and, for most of us, the technical 

paxtkuka are w-at fdgn to our power system 

design experience. 

The amcept of load and source compatibility is not 

new. The need to prwide power with a steady voltage and fqpency has been recognized sin- the inception of the electric utility industry. However, the 

defiriition of 'steady1 has changed over the years, 

refZecting the greater susceptibility of increasingly 

saphisticated electronic equipment to the departure ktaady' anditionn Some of the early concerns were nicker of Wht bulbs due to voltage variations 

and werheathg of elecbPmagnetic loads or hterfer- ence of? cmmmmhtion loads due to voltage waveform 

dhkdm. of these problems led to the 

devekpment of valuntary standards which contributed 

significantly to reducing occurrences. 

Francois D. Wartzloff, Fellow IEEE 

National Bureau of Standards 

Gaithersburg, MD 20899 

More reoently, txmsht vdtage disturbances associated with &at drarits, lightning, and power system 

mdt&hg hare emerged as a major anumrn to manufacturers and users of electronic equipment. Today's 

comp~ sbcut the quality of power are not easily resolved because they involve both a multitude of 

different causes and a variety of specific sensitivities in the affected equipment. Power system 

dedqners, utility companies, lwd as well as source equipment manufacturers, must cooperate with each 

other to find effective solutions. As in the past, 

voluntary consensus standards are needed. 

The issue of gmunling, in partioJlar how to deal with 

noise and safety simultaneously, is complicated by 

cmflkhgphilosophies advocated by people of different backgrounds. Power-oriented engineers and 

signal-oriented engineers often differ in their per- ce@m of cxrmmcn pxblem and solutions. One of the 

goals of the proposed standard is to promote better 

und- of the real issues and to dispel some mkmqhms cn how to avoid or correct electronic 

system grounding problems. 

Since the earliest days of electric power, users have 

aunt& an utilities to pmide electricity that is as free as passible from outages, voltage surges, and 

harmrnlc waveshape dbtmths. Reducing such power 

line has always been a critical concern for utilities. Recently, however, new sources of 

have begun to praliferate, just as many 

pieces of equipment are becoming more sensitive to 

these same power dktutmces. Sclne of these disturbanoea are generated by adjacent equipment, so that 

the utility supply ehnrld not be blamed far the occur- renoa These devalopments have presented utilities 

and users with a new set of complex power quality issues that will require wide-reaching cooperative 

efforts to be resolved. 

A aammcnly applied solutIcn to power incompatibilities 

b to install interface equipment between the raw utility power and sensitive loads. Difficulties in 

assessing this need are: (1) the quantification of 

just hw mu& downtCme is powerrelated, (2) the subjective nature of estimating the cost of sensitive 

bad misoperation attributable to power. The cost/ 

benefit aspgts at the pelem can be addressed from 

the tdmhl point at view in a standard, but detailed economic analysis and specifir: dedsiars remain the 

prerogative of the user allocating the resources. Fozushg on the technical issues, dispelling misconepths, and xemmmmm #xud practices can assist 

the user in making an informed economic decision. 
With that god My defined, the new IEEE Working 

crrmp, Project Pll00, was fonwd to develg, a amsen- sus standard that recommends practices for powering 

md smurdins sensitive eleetrcnic loads in commercial 

Md hdustdl power systems. The document is cur rently at the first draft stage. 

POWERING ELECTRONIC SYSTEMS 

Powering an electronic system is fundamentally the oame as powering any dectrical sy6tem. Estimating the load, makMq aurrent and voltage requirements, or planning far l'izbm~ grPwth Lnrolvc9 the same basic 

inf-~ll~~n. simil.arly, designing an appropriate alectrloal di6tribut.h system, selecting and coordinating overcurrent protection, and assuring good 

valtage zequhth makes use of the same engineering 

practioes. Even the prindplea of availability and 

reliability can be applied to electronic loads in the same way as to any other load. 

An excallent reference Ubraxy ava3lable for designing 

azmmercial and Mustrial power systems of all types 

is the mr Book series. There are currently 

nine Color Beaks in the Series providing recommended 

practioes. The objective is to assist in the design af &el reliab4 and economical electric power systems by providing the consensus of knowledge and 

of the centributing IEEE members. Project 

WOO is intended to yield a new Color Book in the 

series, directed -y at powedng and ground- ing sensitive electronic equipment. 

Computers are just like motors or lights: when the 

power goes away, the elecMQl device quits, and when 

power is restored, it restarts. Of course, it is 

fresuent3y integrity of the process rather than the 

actual device that we must ourselves with. If we lose power to me high speed mveym being fed by 

another high speed conveyor, we can expect a mess samewhere m the factory floor. Likewise, a central 

proeesnn aartrdlling a check printer with a stack of 

~en~acanmandsinvaLatiLe~willmc6t~ely 

be upset by the loss of power continuity. 

Ihe duration of loss of parer continuity is the key 

factor in pI.edicting if a process disruption will ocarr. A large freezer may be able to ae through an axtage of severdl hwrs before caallng lass. We are 

aUowed seands to restore light in a hospital operating roam. Oata pmcedng upset may occur in tens 

of mllllseconds, or in cycles of 60 Hz ac ppwer. 

An artage Is therefore defined differently by different users and prpducera of electric power, sometimes 

creating an obstacle to communication between these 

parties. UtiUty COrmpMies and their paver supply ccntracts will normally only address cutages 

measwad in mhtes. They do nut consider perturba- tions lasting a few seconds or less as the utilities 

resparsib-. When customer equipment is more critical or mare sensitive than the nom. thev consider 

.it the cusbm?s prublem. The speciai POW& quality 

am3 ccntfnuity requirements af a number of commercial 

and industrial loads are described in the mE Oranse 

m Ill. 

Data processing equipment susceptibility to short 

auraUan (cydle to cycle) breaks in power continuity 

shaild nat be wezgenerdlized. First, a computer can ride thmugh a shart aRage. It happens every cycle 

of the ac power sinewave. Secatd, ampubs &a.U be M more sensitive to steady-state voltage variations 

than any ather load. American NationdL Standard C84.l 

establishes steady-state voltage ranges that apply to 

&ll equipment. Furthermore, harmonic dktorcion in 

the utLUty voltage has not been &own to have any more impact on electronic loads than on motors or relays. We conclude that if electronic loads have 

arscegtibilkk to power-lIna disturbances, they also 

have tplerancrs that may reduce the cost and effort 

required to protect them. 

A pndile of data prooessing equipment susceptibility 

(and tnleranca) to variations in the source voltage, 

Pigure l, has been prblLshed in an IEEE 'Recommended 

Practice1 [I], and a NBS IGuidme' [Z]. Presented as a "Typical dedgn objective of power-conscious 

computer hardware designersn, it is not a computer 

industry standad However, ae a typical susceptibil- ity profile, it does denmskah the useful feature of 

increahing ~~ trrlerance with decreasing duratim of voltage pertubation. As a practical matter, 

there are mom d short than long duration. So, by comparing actual disturbance data to 

this profile we bagin to quantify our exposure to 

power-related problems. 

S..l wr. r r h*., 

*w.h.*k.r. -r+..Plor.w* 1 aCK* 

Cahcmaml.*. 

Smmf-n ' 

Figure 1. Typiedl Design Goals of Power-Conscious 

Computer Manufacturers. 

sis Is Draanoslna Power Fmblems 

'we can interpret Figure 1 from an eneryy flow view- 

:point. On the right, we have limitations related to 

the vrcng energy level oasrrhg b the steady state. 

T%.~s lhhth equates to a My state voltage reg- ulatiar problem. For cycle to cycle time intervals, cur a~naern shifts to insufficient energy that occurs during an undervalbge ocnditicn resulting fmm oDrmmon 

overloads or short drrxlita In microsecond time domains, too mu& energy, fn the form of a Lightning or sik&hg event genefilted overvoltage, surfaces as a practical concern. 

This analysis can fadlitate defining power-related p~lems in a way that leads to effective selection of 

power cmdkhhg equipment ar ather appropriate cor- &ve action. The first step is powerline voltage 

'mcnLtoring to determine site power quality. Once a site-specific power quality profile has been established and enemy-related ~xblems identified. one can - prnoeed to out app;opriate power enhancement 

For example, if intermittent undervoltaqes or sqs are LPCorded, then interfaae equipmerrt such-as a motorgenerator might be effective in riding through 

these shorhges af energy. Further discussion of this 

method of aiagnds and prescription is found in [3]. 
The application of Ffgure 1 seans quite straightfccwamlt however, solving a real-llfe power-related 

pxcbbm may n& be. For one thing, the tolerance to 

overvoltage of severdl hundred volts, indicated in 

Pigurn 1, asllumes an Wault at tha input to the 

computer par supply. The electronic equipment tolerance to overvoltages experienced in other 

locations may be signifiantly less. Noise coupled 

into the electrrnic system via many possible alternate 

paths,ascomparedtosurgesanductedalcngthepower 

line, can disrupt data at a 5-volt logic level. 

Related to the noise-coupling problem, is the attemp 

to apply Pigum 1 in the presence of pax gmunding or incorrect surge protecting of equipment. These 

mistakes llay dllow irrternally generated power-related 

problems that totally evade any power interface 

equipment installed, per Figure 1, to protect the dte 

from the outside world. At the same time, such 

interface eqiprment will be adding cost and probably 

reducing overall power system reliability. 

A~~engineeringag~~~required~~~l~ 

address all aspects of the power- and noise-Mated: 

pmblms. In Pmje~A PllW, we axe attempting to present the best explanation possible of the myriad of 

power enhanoanent products and at the same dme maintain a systems perspective. This perspective must 

include &her critical elements of the power system, 

Le. gmunding and surge protection details, and instdllaticPl procedures. We have faund that grounding, 

afscussed next, is a key to noiserelated problems. 

GROUNDING ELECTRONIC SYSTEMS 

Iheatbjectof~isperhapsthemDstmisunderstood, with the result that a large portion of the 

pplems in power sumy applkatims origlnate from inappropriate grounding practices. An 

indication of the complexity of this subject is the 

fact that it occupies over five pages of the IEEE 

dictionary; no wonder misconceptions still abound. 

The existence of this ~r~blem in electsonic svstoms can be srplained by thi different meanings a&uted 

to the term 'qmnd' by the different specialists 

involved ~ta&q with -the 60 Hz or powerzfrequency 

engineer, 'ground1 is syncmymous with 'earth'; its 

functbn Ss to prwide a lcu-impeianca path far return 

& power system fault Currents to the generator. This 

low-impedance path serves a safety role by limiting valtage differenae& during kystem faults aod by allowing sufficient fault currents to assure prompt tripping of the source circuit breakers. 

In this context, ground co~lllections are generally 

large copper conductors, offering low impedance to 

pa~erfrequency current. Emphasis is given to the 

~QB of the connection to 'earth1--that is, the 

subjamat d-by apprc~riate dimensions and number 

of Mven rods in the earth, of buried counter-poise 

conductors, etc. The eafety grounding system is 

passive and shaild n& be called upon to carry rated 

aJrrPnt ex- during intermittent anomalies of power 

system operation such as short circuits. Occasionally, steady-state currents may be present due to 

device Leakage o r t o the nearby influence of strong 

magnetic fields, for instance adjacent wndudon of an arc f'urr~aoe Nevertheless, the steady-state current in grounding conductors should be relatively 

small when compared to phase onductor currents (NEC 

250-21). 

wE and %eferencinu" Must Be Consid~reQ. 

Shirring now to the electrrnic engineer, designing his 

data praassing equipment, 'ground' is synonymous to 

'chassis1. That is, the metal enclosure of the 

equipment, ea&3mes symbdLtcally concentrated into a aingle shiny metal pad at the bottom of the cabinet, 

to whim all anne&cm to 'ground* are routed--and 

n& always by the most direct route. His data pro- cessing circuitry Involves analog or pulse voltage 

signals of generally less than 15 volts, or it involves current loops of a few milliamperes. 

These signdls can be transferred in a balanced, un- gruutded dm& or a single-ended drcuit wW a com- mcn reference. Balanced circuits are isolated from 

graud but their vdltage wfth rssped to ground (com- mon mode) is still significant to the operation and 

potential susceptibility of the circuits. Single-' 

ended circuits carry signals referred to a common patential, most often that of the equipment internal 

chassis, generally called 'reference'. Thus, in either 

case it appears that the electrcllic engineer's concern is that his referencing system carries signal currents 

that can beaDme pdUuted by spurious ground currents 

either through common connection points with the 

earthed system or by common-mode noise coupling. 

Nau entem the systems engineer responsible for the 

hsWbth cd the dorta processing system within one room cd a lmildhg at best, or distributed among sev- eral buildings at worst: to him, 'ground' takes a dale meaning. Tha first is the cacept of the power 

system engineer, the second is the concept of the 

dtdxd~= engineer and, alas, they are not the same. If 

d 

only the first had been called 'earth', and the 

call& tref~l, &s the designers would 

have cocodinated their two distinctive requirements 

ahead af time and much cm-site misery waild have been 

avoided. 

Instead, in the electronics engineer's case, the impedance of his 'reference' system includes a substantial inductive compcnent because of the high frequency 

a€ the signal and noise axrents. The large existing 

oqper cables, dtable for earthing, are not suitable 

far referwdng. A new gmund referwoe grid pmviding a large number of different path Links for the various 

noise frequencies will now have to be incorporated into the system. 

So we see, for electronic loads, we have both safety 

and nab to cmcern oursalves with. Safe operation 

a5 an elazh-hl ar electronic system depends on the 

fntegrity and law impedance of its mrthinq. Undistmbd cprath of the same systems depends on the 

gmm law impedanoe of its eferen 

regardless 0fF-e between the refLence 9 

the earth 121. 

The significance of reference and insignificance of 

earth wmeckh can be illustrated by two examples: 

to prove its reality, consider that sophisticated 

equpent aboard an electronic countermeasures airphie are doing quite well, thank you, without an earth mecticn; back m the grcund we find an fflusfm held by th2? sya Cperaeor, confronted with interferenoe and a refmcinq pdlem, when he contemplates and scPnaimes implements 'better grounding1 by breaking up the ccncrete flax a€ the omputer room to 

install additional ground rods. 

The salutim to this cperatnPs problem is not 'better 

groundhg', but better referencing--such as in the 

uf the airborne electrcnic: system. On the ground 

level, the better referencing can be obtained by 

sstabllshfng a 'gmund grid'. Here the major criterh is lw imwdance at hhh frecruencie~ between any 

two paints of the gmamd grid. Recall that the safety 

gnxurd system shaild pmvide low impeaanCe at low frequencier In a computer room design, the 2lx2' grid 

3 
(d a usual raised floor structure lends iW quite natumlly to prrnriding such a good reference. There 

are of course a few electrical design features that 

aust be prqm3y fncmpcaatsd References [2] and [4] 

already pmvide guidMce for hplementing this sdutjm, and Pruject PllOO will extend the guidance to 

the status of a consensus standard. . .. 

4 at Noise or Sume C-ould Nut Create 

-. 

Ihe first dde affect is associated with the problem 

c& dnxlathg aurents in the ground and reference 

arductoas. WW1cut question, these currents can inject parasitic aFgnals into the data lines. This injecdm k --mode noise qling caused by una- Midable rhsred meetion points between the power 

system gmYd and the dlectronic equipment chassis. 

The problem is real, the side effect is associated 

with how not to solve it. 

lhere have been a number & apparenfly remedies a& as so&5mes by opening up these 

P.cund loops', by creating a 'single point ground', by estabLLshing a 'dedicated/isOlated graund', and 

finally, in the ultimate language contradiction, by hs!aUy a ~flcdng ground'. All of these mncepts, 

dvated by steady-state, low-level noise reduction 

thecny, can and fmpently do werlook the potential 

of power frequency faults. 

Attempts to decouple equipment chassis from earth 

ground for the purpose of isolating and insulating often defeat the basic safety function of earth 

gmmd. !lWq ignora safety and hardware damage issues 

associated with the relatively rare but potentially 

lethal &tuatIons bccurring during power system faults 

and Ughtnhg surges. They also violate the National 

Electric Code as described in 151; such practices 

should be eradicated! 

Continuity of the green wire or metallic raceway 

gm.mdhg system is not incompatible with achieving 

effecthe ~~~ Simply apply the principles 

of the gmurd reference grid discussed abwe and in 

m. Give careful attention to surge pratecllon for 

M data and per &es as presented below. Don't 

resoattotamPeringwithsafetyaspectscUthegmundhg system to cartml nakse. Finally, as a consulting 

engineer, called upon to correct power- or noiserdated problems, beware of both the desire for and 

the existence of dangerous grounding practices. 

Another adverse side effect is assmhted with the 

anfiguratLrr and use cb qmmdhg conductors. It is 

the &aurmw and acnv& at hat is callad 'corn- non mroda* and 'differential modef in multi-conductor 

.ystems Inkidly defined in the context of commun- icationa draritry, these two modes have been applied 

to ac power systems that include phase, neutrirl, and 

graudinJ amdwkxs Here a grcunding CEnductor exists or its hpUm3 by the presence of earthed bodies. 

As with 'refmdng', the situation is confused by 

the blurring of lxundarles between signal processing 

kduxilogy and pawer dellvery/system safety requirements. 

D- on mfxr in eo~dmon mode but aures might 

be erzmeatnty pprqMsed that address cmly differential 

mode dkubame, or vice versa. Remedies to a differsdhl-mode surge can Q.eate a anman-mode dism%- an- For instanoe, a fresuenly applied and very effective memod for common-mode noise elimination is 

the lnstallaticn of an lsohtbn transformer. However, we should not expect this transformer to reliably 

attenuate differential-mode noise (63. Conversely, 

the installatlcn of a single protective device between 

the phase and neutral caductaw, at the end of a long bran*' circuit, wUk (1) clamp the voltage betwaa? 

thge two onductcas, and (2) create a large vdbge, 

ddntoanum~1made,betweenthaneutrdlMdgmunding 

conductors. 

The appmpriate solution, discussed in detail in Refer- m for the cam of a single-phase three-wire 

wstem, consists of providing an additional surge- &mpiG device betwe& the nejrbal and grcunding &- 

ductas. Project PllOO will address the polyphase as 

well as the- single-phase situation. 

With fonethmght, these side effects can be avoided. 

It 16 f&le to design a syetear whem noise problems 

are a~ey &ved withaut resorting to unsafe 

gmunding practkmd We have pointed cut that a reference grid system may k economically incorporated in a camprter room raised floor. Reference [4] descxibes how the reference grid app- uhm used with 

cumputer power centers (isolation transformers) and 

surge arppregLll nawca)rs can oy harmonize 

power and signal gzuu&ng requirements In Reference 

M detaLled guidelines are pmvided for computer room gmmdhg. Hawever, sinsince these dauments do nat am- stiM;e a mnsensus standard, one major goal of ProjeaPllOo~beto~acrnsensusopinion by 

descxibing gocd praaices as wedl as by citing erron- eous practices that should be avoided. 

SURGE PROTECTION 

POW= SySkDS aZ8 exposed influ~ce~ Which can 0oclpl.e en- into the drcuits, .causing a momen- tary ovenrdhge or wercurrent, generally described 

by the term 'surge'. Internal switching of loads in 

these systems can also cmab these momentary events. 

Another phenomenon, the discharge of electrostatic 

charges that have built-up on the human body or objects, can also inject unwanted voltages or currents 

ekchcmic circuits. Finally, another threat is 

related to nuclear explosions effects, under the 

aczonym of NEHP (Nuclear -etic Pulse). The 

prcpmed standard will address the first two of these 

surges, lightning- and switching-related surges. 

Suges can have many effects on equipment, ranging 

hprm no detectable &ect to ampplete destruction. In 

gend devices witlistand increasing valtage suqes amtil dieladric breakdown occurs, 

while electrcnFc devices on have their operation upset befcue hard failure - With increasing surge 

levels, p-.vvely mom inbmse upset oocurs, until 

breakdawn takes place. I£ sensitive electronic data 

prPcesdng equipment shculd be pmtected from even the 

upsetting levels, it is &made that damaging surges 

need to be dealt with before they prcpagate beycnd the 

service entry .for the computer room 171 and [El. 

Definittcas of the level beyad which transient aver- voltages bwnne a Uuaat depend an the type of victim 

esuSpment or praPsn Where electrosPechanicdl devices can generally tolerate short duration voltages of 

twim rating plus 1000 volts, few solid-state devices can tolerate more than twice their normal rating. 

Furthermare, data pmxssing can be affected by fast 

changes with relatively small voltage amplitudes 

compared to the hardware-damaging overvoltages. 

tninq Sumes Can Strike in More Wavs Than One. 

Lightning surge cn-power systms a;r;ur in two modes: 

direct attachmsnt of the lightning path to the power 

systems anductors, and electromagnetic coupling of 

energy krto the pwer system conductors by the radiation of a nearby lighting discharge. 
~hct clttacfiment Lrjd the total lightning current 

Lrto the sy- The ammt mdea range from a few thousand amperes to more than 200,000 amperes. 

Howevartthexap3dctrarrgeofcurrenttA?xqhtheimpedance of the aarducbm prcduom a high voltwet most 

oftenthishiqhvdltage~useseawndary flashoverto 

gmund, divarting ecwe currtmt even 5n the absence of 

an fntentlcndl divezter. As a a, equlpments con- nected at the end of overhead conductors are rarely 

exposed to the full lightning discharge current. 

Muaionofsurgesbyneazby~Mningdischargeisa 

less dramat& but mom frqmk event ' The resulting 

surge dma&d&h are influenced not only by the 

driving fareP-.the eJlpetic field--but also by theresparseafthepwersy~ftsnab.ualoscillat. Thh dual origin makes a general description 

cP the @meti&& but neveztheless a con- sensus & an what representathe threats can be 

expected in various physical environments (91. 

Wheneve a drolft contafning Qpadtanea and inductance b being switrhed on or &, a transient disturbance - because the aurents and vdltages do not 

ma& hhntangusly their final value. This type of 

dbtwimm Js ininescapable and b severity depends on the dative pover level of the load being switched 

compared to the power system in which the switching 

takes plaoe. Most of these disturbances involve the 

respense of the paver system, just as in the case of 

induced lightning surges, so that in practice the 

suqes &senred within a building are similar in their 

diversity, regardless of their origin--lightning or switching. 

More aanplex drcutt phenomena, such as current chopping and restrikes, can praduce Eange voltages reaching ten times the normal drcuit voltages, involving 

en- levels determined by the power rating of the 

elements being switched. These complex surges can have very destructive effects, wen on rugged equipment, and must generally be controlled at the source rather than simply mitigated at the load [93. 

Effective h.oteetixr Teduhues Have Been Dwelmecj. 

Swivalor~~aEtheeqUiPmwt can be adakd in thtee manners: eliminating the cause ab surges (for instance, eliminate lightning, switching, d), producing eqdpmerrt immune to any level of 

avges, no matter how high, or, the obvious choice, 

finding the best economic trade-off where moderate 

avge withatand capability t built into equipment, 

and the worst suxges ocFurring in the environment are duced, by application of suitable pmtective devices, to a level which the equipment can tolerate. 

Because the sau~e ofthe suge is an energy transfer 

phenamencn, involving a any attempt at blocking or - this current by a high impedance 

series path will only produce higher surge voltages 

untjl breakdown ocx;unr Breakdown allows current in an unoartrdlled manner, generally through an unwanted 

path. In contrast, a surge protective device, by 

diverting the offer6 a ]arm, predictable and 

therefore harmless path. 

'Ibis divedm d majar we currents is best accom- plished in two stages The first diversion should be 

pafarmed at the entrance to the building, typically by a mnrentCDndL fauye arrebte, such as a sparkover 

type device, rated for this duty [lo]. Then, any residual wervdltase. hPm the action of the 

Forthisseor~my~' ' , we mxmmend a type adid .tb. da-stalled at the power panel 

af the armplter rwm, at the terminals of a connected 

load, etc. Figure 2 illustrates this coordination 

between two surge diverters and a series impedance. 

A Need for Sdme -ion Is Re-. 

An aspect of m.uge pxtedm that might be overlooked 

is the need to pmde an integrated approach to the 

p- oP the power and data ports o£ an electronksystem. Afakeenseofsecwkymightbec~ted 

when surge pnbzth is installed in the paver supply 

and at the data entry and exit ports. However, unless 

the hsWbth and ground conndcm of these protective devices have been oxrectly implemented, dif - -ties might stiU develop as a result of differ- ences in gmund - rise during operation of the 

protective devices. 

As an exaqL+ Figure 3 shows the case of a computer powerrd by the krilding supply cn one side and interfacing with data lines from cutside sensors on the 

other aide. The power lines are protected at the 

service entrance and the data lines are protected at 

their entry point into the bullding. A surye impinghg on the data Unes and corredly diverted to ground 

at the entry paint will unsvddably produce a rise in 

the potential at the 'ground' point where the data 

line p-ve device is connected, as compared to 

the *groundt point where the power Line pratective 

$2 $5 :x<>, 

COMPUTER rr POWE@ 7' .+- : ry & - 0 n 

I- DATG 

- - 

- PD - Protective Device Zm - Ground flat Impedance 

Vr - PD Voltage Reference Zg - Grounding Impedance 

mice entrance akedxs, can-be dealt with by again FiPure - 3. Differential Graud pchnthl Rise bv Uncodiverting current with a seccndary protective device. oniinated ~pp- af protective bevices 

5 
dwb is &md. The same difference of poten- tials wmld adse it the surge impinged on the parer 

supply port. Thus, the 8ground1 patentiah on the 

power and data kRerfaoe inputs at the computer cabinet viU not be the same, leading to upsets or 

damaga %his phenwiendn is frequently to the dismay af the user who thar.ght that adequate prutection bad 

been implemented with the two devices iwtalled at the 

entry points. 

In such an instance where the entry points are far 

apart, the sduth cDnsists in providing a secondary prct6ztive device far e.a& port af entzy into the wmputer -in& (or entry bthe ampter roaap where the 

computer is installed on an equipotential plane or 

gmund refereme grid), and assuring the same point of 

(graud' arm& 16 used for these protective devices. Hhile the qualitative aspect of this solution 

is gaining recognition, the quantitative parameters 

still need to be investigated. By the time Project 

PllOO nerrrs ~rpppletinq we expect that measurements, 

now in PIUJ- at the National Bureau of Standards, 

will contribute to the quantitative answer. 

We have thus far review& the need and some of the key 

issues that mc*i. us to recommended practices for 

pow& and grrunding dtive ela loads. In 

so doing we recogniK that there are -y many more details to address and many opinions and facts to 

remncile. The following section will layout how we are currently proceeding in this effort. It is 

intended that enaqh detail BE provided to encourage 

discussion and feedback to the Working Group. 

a DDr OV ed SC 0 D@ and PU~OS~ of PlloQ 

Project P1100 is titled nRecomraended Practice for 

Pawering and Gmundlrag Sensitive Electronic Equipment 

(A Color Beak)* The IEEE technical sponsor is the 

Power Systems Engbeehg committee of the Industrial 

Appllcatims Society. A scope has been approved as follows: 

*This project recommends design, installation and 

practioPs for elecfrrcal per and grounding (including - safety and noise control) of sen- sltive eledxmc lm3.s such as computers, industrial 

controllers, and other electronic data processing 

eqdpment used in oDmnaercial and industrial applications.' 

The stanQrds prq/ect request (PAR) was submitted in June 1985 and approved by the IEEE 

Standatds Board in September. A 'strawmanl atline 

for elevem cfiapters was developed and chapter objectives translated into a set of directives to chapter 

rnrthora Internal and extend rwiew procedures have 

been established. Preparation of a first draft is 

underway. 

Meanwhile interest continues ta grow. A number of 

trxtondls have been dfered bd31 inside and outside of 

IEEE. As an apparent offshoat of deregulation, the 

utility industry is beginning to look at markefing a higher quality electric service with power 

conditioning equipment incorporated at increased 

electric energy rates. Still, there is no consensus standard available as a reference for electrical 

engineers responsible for the power system design. 

Help is needed in developing, writing, and reviewing 

lMROlXJCTION - mers the pupcse and backgruuna 

in much the same way as in this paper. 

SCOPE - as quoted in this paper. 

DEFINITI.CHS - thk daapter provides definitions 

not atherwise available in IEEE Standards or as 

necessary to improve readability. The Chapter Qlairperscn is mPmvost Marshalu with regard to use of undefined terms or acronyms in other 

chapters. 

~NEED~DELINES-thiscfiapterisintended to identify the relevant codes and standards as well as the existing electrical environment 

that sensitive electronic equipment is typically 

subjedd b in the field. Topics include coor- dinatim with other guidelines, electrical safety, - quality, grounding, surge protection, 

Ufe-safety, and telscommunicatien systems consideraticns. These guidelines are established as a basis for the treatment of performance requireaPents and recommended practices in subsequent 

chapters. 

FWfWElWMS - this chapter trtroduces the reader 

to the fundamental technical information neces- mxy to understand and to apply ~~~~mmended prac tices for dedgn af a compatible and essentially 

hazan3-free interconnection. Fundamentals not 

unique to sensitive electronic and/or electrical 

equipment will be treated very lightly, or only 

by reference to other IEEE Standards and appropriate books on recommended engineering practtm. Fundamentdls to be covered include power 

system quality, !2hmnic data processing equipment power qualxty requirements, load and supply 

annpatibi?ity, grounding bonding and shielding, 

protection, and wiring practices. 

REa3KMWDED DESIGN/DISTWATION PRACTICES - k 

the main message of this publicatim and is expected to be most difficult to gain consensus. Vagueness at this point wculd be a disservice to 

the reader. We intend to .put down on paper our ddve enqineering e.ce and judgment to 

pinpoint recommended pra-ces. The proposed 

subjects are general discussion on performance 

and safety, 60 Hz ac systems, 400-480 Hz systems, 

and Ufe-safety system interfaces and controls. 

KXS-REam4mDED DEsIqSTWATxaN F'RACPICES - 

is the chapter in which we very daliberately 

a#ack "wives8 talesn and raise 'warning flags," 

but are careful nct to htrduce any new mncepts or materials Comnwolly abSezYBd mn-~mmended 

practices will be emphasized. The chapter is 

aRllned by specific design topic to facilitate 

quick retrieval from the reference. 

SPECIAC MEASVRENENTS AND INSTRUMENTATION - 

presents information on special measurement 

req[l-ts and on available equipment that are unique to investigating and diagnosing problems 

in power systems that serve sensitive electronic 

equipment. The proposed approach is to start 

with dc mehsurements of voltage, current, and 

power and to progress through the fundamental 

frequencies (60 and 415 Hz) to harmonic and 

higher frequencies, up to 300 kHz. RFI/EMI wiU 

be covered by reference only. 

- - 

this standard. the technical infomatim base established in the 

6 
Tale 1. Standards Coordination Plan 

INWSTRIAL APPLICATIONS SOCIETY --er system Design sc m, and lIhits Basics of Ccf power sptamr 

-wrgmcy & St~ndhy sc QmmLEWi General need, ilPiC/&ttuiu 

-Grounding SC EUsLBQk Safe grding practice 

-Reliability SC Pwer system reliability 

-Industrial Control Con Needs of electronic controls 

-Static Power Converter Cou IECE 519 %UIDE* Converter design/interface 

POWER ENGINEERING SOCIETY -Pov.r Generation Cou Grounding, noise control b UPS 

-Tranwission/Dist. cou -78, IEEE 519 .Z?.CD PRACn Suvice to critical loads 

-LV Surge Prot. Device SC ANSI C62,P-932 Surge envLro~~~t/testing 

EISLTR(IRUGLlET1C COMPATIBILITY SOCIETY 

-UC Standards Cam P-626 Signal grounding practice N.DIIIYI...MIU-II - UPIOI11. SPONSOR (OUTSIDE IEEE) ST- AffLVITY BASIS FOR COORDXUATION -I=----= ---- YUIIIPlUIUU 

NATIONAL BURUU OF Sl'AW0ARD.S 

-1nst. for Cow Sci. & Tech ?IPS pub I94 dlectriul power for ADP CfflFVTER BUSINESS WIF?fEXT MWUFACNRERS WSC 

-Power Interface SC (LSC-3) Not a stds making body Source of nanufacturerr data 

NATIONAL ELECTRICAL IUHUFAClURERS ASSC 

-Power Electronic6 Section NEnA STD Pub/No. PE 1-1983 Uninterntptble pawr sySta.s UNDERWRITERS LABORATORY UL 1 478. 943 b 1449 ADP safety, transient tests 

NATIONAL PLRE PROTECTION AGC NFPA 70 L 75 Installation safety, fire prot. INSTRUMEWI' SOCIETY OF MIRICA Naeds of hutrumants - pm- apters, and p- practical as- and di5m-e nQveOOmmended P- Ahead of us 

p-a wogis by a engineer k5 a tough and the-co~s~aeing job of sorting out or technician. A section on interpreting and various PO- of view bating various other 

applying pubushed power quay survey data related standards activities. It will be several 

included; however, the chapter emphasis is the Ym befm the task be ~rq~erly -. This 

appWtFon of survey data from the user% own intducb~ Paper k intended to be the first of 

site. several preceding publication of the consensus standard. The Project PllOO Working Group will 

10. SELECTION AND VERIFICATION OF EQUIPMENT AND t+elamW ~0lUmelIt.S on the COn~pts presented in this 

MATERIALS - presents the myriad of available paper and contributions to the final document. 

power enhancement equipment from a basic technology, performance, and functional point-ofview. A bbmd of mufaehrrer and user input is REFERENCES 

required. Manufacturers will be encouraged to 

prwide generic rather than marketing details of [l] IEEE Recommended Practice for Emergency and 

equipment HOW tn verify equipment performance Standby Power Systems for Industrial and Comby testing is also covered. mercial Applications, Dae Book, Std 

446-1980 

11. CASE HlSrOKIES - is intended to provide explicit [2] National Bureau of Standards, Guideline on examples cb redl-world per£ormance and/or safety Ekdrbl Power for ADP Installations, Federal 

problems that have been encountered in the Infornation Processing Standards Publication, 

field. l9camples are cfiosen that did not confonn, FIPS PUB 94, Sep 21, 1983. 

in one or more ways, to specific recomnended [3] T.S. Key, NDiagnosing Power Quality-Related 

practices presented in this publication. Special Computer ProblemsIw Transactions on care will be taken to ensure that the selected Illdust-, VOL IA-15, 110.4 , pp 

examples am KEP key-paints of Chapters 381-393, July/August 1979. 

6 and 7, rathersteresting, but obscure 141 W.H. Lewis, wRecommended power and signal ones. grauding for antsdl and computer rwrn~,~~ IE;EE 

Transactions on Industrial A~~lications, vol. 

12. APPENDIX (as required) IA-21, No 6, pp. 1503-1516, Nov/Dec 1985. 

[5] W.H. Lewis, nApplication of the NEC to the 

13. ANNOTATED BIBLIOGRAPHY hstaUkh of sensitive electronic equipment," ns on 1- Au~Lications, 

14. INDEX vol. IA-22, No 3, pp. 400-415, May/Jun 1986. 

[6] F.D MartzkCf, "The propagation and attenuation 

coordination With Other Codes and Standards of surge voltages and surge current? in 

lovyaltaqe ac power drahi, 7JEE-T --rrtlow 

hs with most standards activities, there is a whole Power Ao~aratus Svateme, vol PAS-102, pp. 

array of existing and proposed standards that are 1163-1170, May 1983. 

related to the tectmt3al scope. Careful coordination [7] F.D. Martzloff and H.A. Gauper, Jr., "Surge and 

fs critical to ensure proper treatment and avoid High-Requency propagation in Industrial Power 

unn~ogsil~y werlap. Thus far we have identified or Lines," 

have been requested to coordinate with the activities Wations, vol. IA-22, pp. 634-640, 

listed in Table 1. July/August 1986. 

[a] D MarUloff, "~oarrljnatirn of surge protectors in 

low-voltage ac power chdts;* DCONCLUSIONS ADDaratus Svstems, vd PAS-99, pp. 129-133, 

Jan/Feb 1980. 

A cons.asus standard is needed for powering and [g] IEEE Guide for Sqe Vdltag- in Low-Volbge AC ~ensitive @equipment This stand- Power circuits, ANSI/IEEE C62.41-1980. 

not *y and present [lo] IEEE Standard for Sume Arresters for AC Power practioes but also fd- and dispel lpisconceptions Circuits, ANSI/IEEE C62.1-1981. 

7