IEEE Transaction on Power Apparatus and Systems, Vol. PAS-103, No. 10, October 1984

THE INFLUENCE OF WOOD POLE PRESERVATIVtSON WOOD FIRE AND ELECTRICAL SAFETY

R. FilterOntario Hydro

Abstract

The electrical perf ormance of two water-borne woodpole preservatives (ACA and CCA) has been compared tothat, of pentachlorophenol preservatives. Laboratorytests have indicated that for water-borne preservativetreated poles, fire inception currents are two tothree times greater than for comparable penta-chlorophenol treated poles. This is likely due todifferent pole fire evolution mechanisms. Wood poleand hazard models are developed and augmented withfleld tests to demonstrate that, from the point ofview of pole contact near ground level, a comparabledegree of safety exists with both water-borne andoil-borne preservative t.reatments .under normaloperating conditions. With. fire inception currentsflowing, poles treated with water-borne preservativescould result in painful shocks.

INTRODUCTIONQ

Methods currently in use to treat wood poles toextend their service life usually revolve around theimpregnation of the wood with either oil-borne orwater-borne preservatives. Although many types ofpreservatives have previously been stud-ied [1,,23], the list of candidate preservativechemicals is constantly growing so that the more re-cently developed substances have not been extensivelystudied, especially from the viewpoint of their elec-trical effects. Further, as the availability of thehistorically preferred wood species of cedar and pinehas decreased, alternative wood types have come underincreasing scrutinv [1,2]. Thus, the combination ofnew candidate wood pole species with equally new can-didate preservative treatments, or the combination oftraditional wood pole treatments with new wood specieshas resulted in uncertainties relating to wood poleperformance and safety.

This paper presents results of electrical tests onseven different wood pole species in combination withthree preservative treatments. Of primary interest inthe tests was the susceptability to fires of eachcombination of preservative treatment and wood type;and, the electrical safety of each combination shouldit be contacted near ground level.

Principal conclusions of this work can be-summar-ized as follows:

- Water-borne preservative treated woods exhibitbetter immunity to fires than oil-borne preserva-tive treated woods.

- From the point of view of safety, the performanceof water-borne and oil-borne preservative-treated

84 T&D 316-6 A paDer recommended and anorcvedby the IEEE Transzissicn and Distribution Co=it:teeof the IEEE Power Enaineerinz Society for oresenta-tion at the IEEE/PES 1984 Transmission andDistribution Conference, Kansas City, Missouri,April 29 - MXay 4, 1984'. Manuscript submittedNovember 2, 1983; made available for printingFebruary 29, 1984.

poles is comparable in that no hazard to linemencontacting -the poles near ground level exists.Even if pole fire inception currents are flowing inthe poles, no perceptible currents will reCult inlinemen from penta-treated poles, and body currentsof the order of 4 to 6 mA, a perceptible but non-hazardous level, may result from contact-with polestreated with water-borne preservatives.

Wood Species and Preservative TreatmentsIncluded in This Study

The seven different species of wood pole, alongwith the three preservative treatments used duringt;hese tests are listed in Table 1 below.

Table 1

* Ammoniacal Copper Arsenatet Chromated Copper Arsenate

Of the preservative treatments used in the tests,pentachlorophenoli usually called simply penta, is thecommon oil-borne treatment specified by many utilitiesfor full length pressure treatment of pine poles.Ammoniacal Copper Arsenate (ACA) is a water-borne pre-servative treatment originallx, marketed under thetrade name "Chemonite". It consists of compounds ofcopper and arsenic rendered water soluble by thepresence of ammonia in the treating solution. Tvpe CChromated Copper Arsenate (CCA), is also a water-bornepreservative and is composed of chromium (as CrO-)copper (as CuO) and arsenic (as As2O3).

Evaluation Methods: Fires and Safety

The susceptability of the combinations of. woodspecies and preservative treatments to fire was evalu-ated by subjecting prepared pole stubs treated withthe candidate preservatives to increasing levels ofcurrents until a fire occurred. Current levels, timeto fire inception and infra-red photographs wererecorded to provide quantitative performance compari-sons.

To evaluate the electrical safety of poles treatedwith each of the preservatives., the resistivity oftreated stakes was determined, then along with inf or-mation relating to pole preservative penetrationdepths, a two-layer model was adopted to describetreated pole behaviour. This model was augmented withdata collected during field tests of in-service penta

-0018-9510/84/1000-3089S01 .00 1984 IEEE

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Wood Pole Treatment Used

Southern Yellow Pine PentachlorophenolRed Pine PentachlorophenolScots Pine Pentachilorophenol

Yellow Cedar (ACA)*Western Cedar (ACA)*Spruce (ACA)*

Red Pine Type C (CCA)Southern Yellow Pine .Type C (CCA)tJack Pine Type C (CCA)T

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treated and untreated poles. The, final product ofthese procedures took the form of graphical compari-sons of the safety of each candidate treatment type.

Treated Wood Fire Susceptibility

Substantial work has been carried out by other re-searchers to investigate the evolution of utility polefires [5,6,7,81. In that body of work, both the testcircuits and the methods of sample preparation havebeen developed. In this study, fire tests carried outwith each combination of wood type and wood preserva-tive treatment were set up consistent with the work ofprevious researchers. It was recognized that pole andcross-arm geometries as well as grounding facilitiesaffect pole fire evolution [7,8]; however, the objec-tives of this test were to compare the relative per-formance of treated woods under one set of controlledconditions, rather than to study actual in-serviceconfigurations accurately. For this reason each can-didate pole, in the forni of a stub about 1.5 m long,was fitted with a pair of band electrodes spaced about45 cm apart. A section of wood about 5 cm wide half-way between the bands was taped, and the pole wasthoroughly wetted. The tape was subsequently removedto provide a dry band. Sufficient potential wasapplied between the two electrodes to produce severallevels of current flow through the wood. The effectsof this current were then assessed to determine valuesof fire inception currents.

Table 2 presents the results of these tests.

In this table, results have been grsDed and aver-aged according to treatment type. Thib is consistentwith studies indicating the dominant role of treatmenttype [1,2] and allows performance comparisons.

Several additional observations relating to theevolution of a pole fire with each type of preserva-tive treatment can be made since it became apparentduring these tests that two distinct mechanisms ini-tiated pole fires.

First, for the water-borne treatments, poles caughtfire only after a prolonged drying-out period. Initi-ation of current flow heated and dried the pole sur-face until only the moisture still remaining in thecracks of the stub provided the current path. Sincethere were usually several cracks, current flow wasshared and no further temperature increases wereobserved. Gradually these cracks dried out and moreof the current became concentrated into fewer cracks.At this point significant temperature increases were

observed and the first evidence of wood charring wasdetected. As the last remaining cracks dried, char-ring continued until a carbon path formed in the woodbetween the two band electrodes. Eventually thecurrent flowing in this carbon path generated suffi-cient heat to start the wood glowing. This in turngrew into an open fire. The entire process usuallytook 20 or more minutes. This sequence of events isillustrated in the infrared photographs of Figure 1.

1.START. NOTE ELEVATED 2. NOTE THE UNIFORMTEMPERATURE BAND IN HEATING OF POLECENTRE. SURFACE.

3. POLE DRY. BEGINNING 4. CONSOLIDATION OFOF TRACK. TRACK.

FIGURE 1THE EVOLUTION OF A POLE FIRE WITH WATER

BORNE PRESERVATIVE TREATED WOOD

In contrast, poles treated with the oil-borne pre-servative tended to develop a hot single track insidea crack almost immediately. Very little surfaceheating was observed. Furthermore, charring of thesingle track usually began in less than 5 min and asit progressed, substantial volumes of smoke and gaswere generated. As well, the glow condition usuallydid not persist and gradually evolve to open fire, butrather, open flame tended to result from the ignitionof the by-product gases attendant to charring thepenta treated wood. Penta treated pole stubs tendedto burst into flame rather than evolve to it. This isillustrated in Figure 2.

ABLE 2

POLE FIRE INCEPTION THRESHOLDS

REATMGENTCURRENT AVERAGE INCEPTION AVERAGE COMMENTSTREATMENT CURREN (mA) CURRENT (mA)(mA)~~~~(mA) ____

SCOTS PINE PENTA 2 2 BOTH SAMPLES IGNITED IN~3 MIN. HEAVY SINGLE

RED PINE PENTA 2 2.5 2 3. 3 TRACK. ABUNDANT SMOKEJACK PINE PENTA 2 4 AND GLOWING PRECEDESS.Y. PINE PENTA 4 5 FLAME. SPARKING.W. CEDAR ACA 13 15 SINGLE TRACK AT HIGHY. CEDAR ACA 12 12.7 is is CURRENTS. VERY LITTLEY. CEDARACA12 12.7 15 15

~~~SMOKE AND SPARKS.SPRUCE ACA 13 15 GRADUAL IGNITION.JACK PINE CCA 5 8 SINGLE TRACK AT GLOW CURRENT.S.Y. PINE CCA 6 4.3 10 7.3 SOME SMOKING AND SPARKING.

RED PINE CCA 2 4 SPARKING AT LOW CURRENT.SURFACE TRACKING. HEAVYSINGLE TRACK 6 MODERATE SMOKE.

* THE GLOW CURRENT IS THE CURRENT AT WHICH PERSISTENT INCANDESCENT GLOW WAS OBSERVED** THE FIRE INCEPTION CURRENT IS THE CURRENT AT WHICH FLAMING WAS OBSERVED.

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FIGURE 2EVOLUTION OF A POLEFIRE WITH OIL BORNEPRESERVATIVE TREATEDWOODNOTE:IMMEDIATE SINGLETRACK FORMATION

Figures 3 and 4 illustrate the difference in thenature of the flame and in the nature of the trackingbetween stubs treated with two types of preservativetreatment. In particular, Figure 3 contrasts therelatively violent flaming of penta treated wood withthe more sedate flaming typical of water-borne preser-vative treated wood. Figure 4 illustrates the muchdeeper tracking of the water-borne preservativetreated wood as compared to the penta treated wood.

Wood Pole Safety

Three stages were involved in the assessment of thesafety of poles. First, previously published datadescribing the electrical performance of treatedstakes was augumented, where necessary, with tests to

WATER BORNEPRESERVATIVETREATED POLE

OIL BORNEPRESERVATIVETREATED POLE

FIGURE 3POLE FIRE EVOLUTION

DEEPTRACKSHALLOWTRACK

WATER BORNEPRESERVATIVETREATED POLE

OIL BORNEPRESERVATIVETREATED POLE

FIGURE 4COMPARISON OF TRACKING:

WATER BORNE TREATMENT VS OIL BORNE TREATMENT

describe the behaviour of stakes for which publisheddata was unavailable. The methods and techniquesdescribed in the literature were closely fol-lowed [1,2].

Secondly, because there are substantial differencesbetween small stakes and full sized poles in the dis-tribution of moisture and preservative, and since ithas been demonstrated that moisture content and pre-servative treatment are the dominant factors influenc-ing electrical performance [1,2,5], a simple wood polemodel to account for these factors was adopted utiliz-ing the stake performance data and preservative pene-tration depths as specified in treatment standards[11].

Finally, a simple electrical equivalent circuitwas developed utilizing the pole model, to determinethe body current resulting from contact with candidatepoles treated with each of the three preservativetreatments. The results obtained from this model werethen augumented by a series of field tests of in-service penta treated poles to place the calculationsinto a practical perspective.

100CJACK PINE-JACK PINE (FROM TESTS)

10 SCOTS PINE

\ \\\ WEST. CEDAR(UNTREATED)

,-1

u7 RED PINE-

SOUTH..Z YELLOW PINE

0.1

'FROM PUBLISHED DATA /1,2/

0.0 I I I0 2 4 6 8 10 12 14 16 18 20 22 24 26 20MOISTURE CONTENT I%)

FIGURE 5RESISTIVITY VS MOISTURE CONTENT FORPENTA TREATED AND UNTREATED WOOD(FROM TESTS AND PUBLISHED DATA)

The Wood Pole Model

Figures 5, 6 and 7 present previously publishedresults and the results of tests to determine theelectrical performance of treated stakes. The domi-nating influence of treatment type and the secondaryeffects of wood species are evident. So much so thatcomparatively small errors will result if the varia-tions due to wood species are suppressed entirely andthe performance of the candidate wood stakes isdescribed by a single averaged curve with preservativetreatment as the parameter. This has been done inFigure 8.

When the properties of the treated wood (ie, in theform of stakes) have been determined, this informationcan be generalized to describe the behaviour of woodpoles. Several assumptions have been made in order toaccomplish this generalization. First, it was assumedthat the moisture distribution throughout the pole isuniform. Secondly, it was assumed that a well definedboundary exists between treated and untreated woodinside the pole. Thirdly, in what follows, it wasassumed that both the diameter and the moisture con-tent distribution along the length of the pole remainsconstant and fixed at values found at about 1.5 mabove earth. Under those assumptions, a preservative

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treated pole can be described as composed of twocircular regions. The outer region is composed ofuniformly treated wood to a depth specified byReference 11, and the inner core of the wood pole,occupying the remaining cross-sectional area, isuntreated wood.

This configuration is illustrated in Figure 9.

From Figure 9 the wood pole model can be developedas follows:

R = PTQTRT-AT R =u Au (1)

where

RT = resistance of treated wood (Q)Ru = resistance of untreated wood (Q)Au = cross-sectional area of untreated wood = 11r2 (cm2)AT = cross-sectional area of treated wood =T(R2-r2and pT,Pu are the resistivities (2-cm)oof treated

and untreated wood respectively (ie, stake data).

If Ra is defined as the apparent resistance of thepole and is composed of the parallel combination ofRT and Ru and ifIf RI = tT uthen

Raa r T + Pu - (R

where Ag = HIR2 = geometric cross-sectional area

FIGURE 6 FIGURE 7CCA TREATED WOOD ACA TREATED WOOD

(FROM TESTS) (FROM TESTS)From Figure 11

RI~~~~m R + R + R

c m p

where

I body current (A)Rm body resistance (Q)Ip= pole current below lineman contact (A)Rp = resistance of 1.5 m of pole (Q)Rc = hand contact resistance (0)

generally, Rc > Rm.cm

(2) ThereforeR

I Fs P Im R +R

c p

(from field tests)

(4)

This can be re-expressed in terms of an apparentwood pole resistivity, Pa, as

PT Pu

pu (R) ( p )+ R PT-u

Figure 12 shows the relationship, obtained duringfield tests, between contact resistance and woodmoisture content of penta treated and untreatedpoles. From the figure, typically.

(3)R = lo-0.14 M.C. + 8.9c

(5)

Using Equation (3), the resistivity versus moisturecontent relationship for a wood pole can be determinedfrom the properties of the treated and untreated areascomprising the pole, and from pole geometries.

Figure 10 summarizes the results of these proce-dures and expresses them as average values groupedaccording to treatment type.

One interesting observation can be made fromFigure 10 and the effect of the two layer pole model.Generally, the effect of the model has been to mini-mize dif ferences in perf ormance between the water-borne and oil-borne treated wood poles. The compara-tively large untreated central core of the pole hasresulted in wood pole performance adjustments whichtend to reduce the effects of the treatment type fromthose evidenced solely by stake data.

THE HAZARD MODEL

Using the resistivity versus moisture content rela-tionship of a pole, an assessment of the hazards pre-sented to personnel contacting the pole near groundlevel can be made as follows.

Assuming a total pole current I flows in the pole,the electrical model used to determine wood polesafety is shown in Figure 11.

where M.C. = per cent moisture content.RC= contact resistance (Q) .

Thus, if

im= body current from penta treated polesR = resistance of penta treated pole (0)Imp = body current from sample pole (A)R = sample pole resistance (Q)

Im5

Imp

Rp5/ (RC RPS )Rp / (Rc + Rp )

p p

Rp5

Rpp

(A)

R + Rc p

R + Rc p5

(6)

Equation 6 combines the information from pole andelectrical models with field test data and provides aquantified per unit hazard assessment in terms of bodycurrent shunted ifito a man contacting the pole nearground level.

The Relative Safety of Poles Treated WithWater-Borne and Oil-Borne Preservative Treatments

Any assessment of the electrical safety of wood,poles should be centred around the amount of current alineman might shunt away from the pole when he comesinto contact with it. As is illustrated. in Equa-tion (6), this body current will be determined by

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several things, including the resistance of the lengthof pole shunted by the lineman, the contact resistancebetween the lineman and the pole, and the lineman's-body resistance. Both pole resistance and contactresistance are determined by the properties of thespecific treated pole under consideration, and by itsmoisture content.

1 __

x

C:

I-

L-(Au,

UNTREATED WOODPITREATED WOOD

(a)PHYSICAL MODEL

FIGURE 8

(b)EQUIVALENT CIRCUIT

FIGURE 9WOOD POLE MODELS

001_

) MUNTREATED(

\ PENTA

z

FOROODOLESAVERGEDACAODNCCA

a.0.1

0.01 L L0 6 8 10 12 111 16 18 20 '22 241 28 30MOISTURE CONTENT()

FIGURE 10APPARENT RESISTIVITY VS MOISTURE CONTENTFOR WOOD POLES AVERAGED ACCORDING TO

PRESERVATIVE TREATMENT

During the development of a hazard model to deter-mine body current, it became apparent that body resis-tance was typically more than an order of magnitudelower than both pole and contact resistance values,and so could be neglected. Thus, only pole resistancevalues, as determined from the two layer pole modeland contact resistance values as determined duringfield tests with penta and untreated poles were used

in the determination of body currents. It is possiblethat the contact resistance will vary somewhat betweenwater-borne preservative treated poles and polestreated with penta; however, from our testing itbecame clear that contact pressure, contact location(ie, on knots or cracks) and hand conditions (ie,clean and dry versus moist) also played importantroles in contact resistance values, so much so that ithas been assumed in this study that contact resistancedifferences due to variations in treatment type aresecondary effects. Thus, contact resistance valuesdetermined for penta and untreated poles are con-sidered representative of typical values to beexpected in the field, independent of treatment type.

In the following, Figures 13 and 14 provide compar-isons of the amount of body current flowing in a mancontacting poles near ground level treated with eachof the three treatment types. Figure 15 and Table 3present the results of field tests and provide insightinto the significance of the data on Figures 13 and14.

The Basis for Performance Comparisons

There are two safety-related concerns addressed byFigures 13 and 14. First, Figure 13 addresses howmuch body current will result in a man contacting thewater-borne preservative treated poles as compared tohow much body current would flow if he had insteadcontacted an identical pole treated with oil-bornepreservatives. In effect, this is a per unit bodycurrent comparison between pole treatment types basedon Equation 6. Although Figure 13 provides a means ofdirectly comparing the relative amounts of bodycurrent resulting in a man contacting the pole under avariety of moisture content conditions, it does notprovide a direct hazard assessment since the bodycurrent in milliamps is unavailable.

Figure 14 provides body current in milliampers whenwood fire inception currents, as may result frompolluted insulators, are flowing. Equation 4 and 5were used to generate Figure 14.

Test Identify Typical FieldConditions for Penta Treated Poles

Figure 15 and Table 3 present the results of fieldtests conducted during five consecutive days of fairweather (sunny and dry at 12 to 15C) and two days offoul weather (continuous drizzle at 12 to 150C).These tests are described in the appendix.

From Figure 15 and Table 3:

1. Fair weather moisture contents typically varybetween about 11% and about 18%. Fair weatherleakage currents flowing in penta treated polesare capacitive in nature and well below 1 mA,even for the 44 kV circuits tested. This meansthat as far as fair weather performance is con-cerned the differences in body current resultingfrom contact near ground level with water-borne

FIGURE 11WOOD POLE HAZARD MODEL

100a

u

< 10F-LAS(A

U

z0u

z

I 0.1

0-014 6 8 10 12 14 16 18 20 22 24 28D S32MOISTURE CONTENT (%)

FIGURE 12HAND CONTACT RESISTANCE

VERSUS WOOD MOISTURE CONTENT

1.2-.,~~~~~~PENTA

0.8

0.4 A *---..

0 2 4 6 8 10 12 14 16 18 20 22 24 26MOISTURE- CONTENT

*PER UNIT BODY CURRENT=BODY CURRENT FROM WATER-BORNE PRESERVATIVE TREATED POLESBODY CURRENT FROM OIL-BORNE PRESERVATIVE TREATED POLES

FIGURE 13

z 10 O0-9

Z 8X 77

-J6_LI

E zU *C

>. 1 PERCEPTION ---0

O 2 4 6 8 10L 12 14 16 I18 20 22 24 2% MOISTURE CONTENTFIGURE 14

U. Z8A FAIR WEATHER~~~_ 6- ~9FOUL WEATHER

>< 4-

0-10 12 14 16 18 20 22 24 26 28 30 32% MOISTURE CONTENT

FIGURE 15

preservative and oil-borne preservative treatedpoles is below perception values and thereforeinconsequential.

2. Foul weather moisture contents typically varybetween about 20% and 30%. Leakage currentsduring foul weather are somewhat increased fromthose during fair weather since the line insula-tor resistance is reduced and so permits morecurrent flow. Even so, current levels in pentatreated poles were still well below 1 mA, and sono hazards exist during pole contact.

Safety-Related Observations (Figure 13 and 14)During fair weather conditions with moisture con-

tents in the 11% to 18% range, Figure 13 illustratesthat body currents resulting in a man contacting awater-borne preservative treated pole will be com-parable to or less than currents resulting from con-tact with a similar penta treated pole. These bodycurrents wi.ll be below perception thresholds (seeTable 3),

On the other hand, when pole fire inceptioncurrents are flowing, such as might occur withpolluted insulators after a brief rain, Figure 14shows that water-borne preservative treated polescan result in a higher, perhaps even painful, elec-trical shock than penta treated poles would.Interestingly enough, should the foul weatherpersi.st long enough to raise the pole moisturecontent (ie a day or two) body currents in a mancontacting water-borne preservative treated poles.would reduce to levels comparable to orless than those from penta treated poles. Thus, thereappears to be a define "window" during which per-ceptible body currents could result from contactwith water-borne preservative treated poles.

CONCLUSIONS AND COMMENTS

1. Woods treated with water-borne preservativeshave substantially higher fire inception thresh-olds than woods treated with pentachloropherol.While pole fires result from a combination offactors, including cross-arm geometries andgrounding arrangements, the greater intrinsicfire resistance of woods treated with water-borne preservatives should result in poles thatalso have greater pole fire resistance.

TABLE 3

FIELD TEST RESULTS:POLE CURRENTS AND MOISTURE CONTENTS

LINEVOLTAGE WOOD(kV) TREATMENT

AVERAGE MOISTURECONTENT (6)

FAI R FOULWEATHER WEATHER

16.5 26.113.9 -15.4 25.5

AVERAGE POLECURRENT (pA)FAI R FOULWEATHER WEATHER167.0 408.039.4 -17.3 31.5

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0TPA

TYPICAL *

* 2.4z

s 2.0SU 1.6a0

az

S

44.0 WEST. CEDAR PENTA & UNTREATED27.6 WEST. CEDAR PENTA & UNTREATED8.3 JACK PINE PENTA

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2. During normal operating conditions, body cur-rents in a man contacting any of the combina-tions of pole species and treatment typesincluded in this study will be below perceptionlevels and present no hazards (see Figure 13,Table 3).

3. During foul weather conditions and if wood fireinception currents are flowing (as a result ofpolluted insulators), body currents as high as4-6 mA are possible with poles treated withwater-borne preservative treatments. These bodycurrent levels are non-hazardous, but may resultin a painful electric shock (see Figure 14). (A) TEST SET-UP *(B) EQUIVALENT CIRCUIT

FIGURE 16

REFERENCES

[1] Katz, A.R. and Miller, D.G., "Effects of WaterStorage on Electric Resistance of Wood", ForestProducts Journal, Contribution P-17, July 1963.

[2] Katz, A.R. and Miller, D.G., "Effects of SomePreservatives on the Electrical Resistance.of RedPine", American Wood-Preservers' Association,Vol 59, 1963, pp 204-217.

[31 Hunt, G.M. and Garrett, G.A., "Wood Preservation"A Text, 3rd Edition, McGraw-Hill, 1967,pp 304-305.

[4] Wood Handbook, US Forestry Service #72 Revised,1974, pp 3-22.

[5] Canadian Ohio BrassTechnical Study of (Suggestions for TheiPart II, May 1947.

[6]

[7]

,,High-Tension News, "ACauses of Pole Fires andr Practical Preservation,"

Ibid, Part II, June 1947.

Kurtz, M., "Wood Crossarm Burning Caused byCurrent Leakage", Ontario Hydro Research News,Vol 8, No 1, 1956, pp 24-29.

[8] Ross, P.M., "Burning of Wood Structures byLeakage Currents", AIEE Transactions, Vol 66,1947, pp 279-287.

[9] Dalziel, C.F., "Electric Shock Hazard", IEEESpectrum, February 1972, pp 41-50.

[101 Bridges, J.E., "An Investigation on Low-ImpedanceLow-Voltage Shocks", IEEE Trans on P.A.S.,Vol P.A.S.-100, No 4, April 1981, pp 1529-1537.

[111] CSA Standard 0.80.4, "Preservative Treatment ofPoles by Pressure Processes", 1979.

Field Test Methods

- To determine the resistance per unit length, asteel band electrode was fastened to the pole atabout shoulder height (1.5 M). A copper ground rodwas driven into the ground about 0.6 M, very closeto the pole base. High voltage (ie, 1 kV) dc wasapplied between the electrodes and circuit currentwas recorded. Together' with the applied voltage,the dc current yielded the pole resistance, Rp,for a pole length of about 1.5 m.

- To determine the total pole current, Figure 16shows the physical arrangement and model. Fromthat figure:

Suppose a total current, I, flows in the pole;

then, I = Ip + Itwhere Ip = pole current below upper electrode

It = current shunted through ammeter

and

IR = (R + R + R) It A-1

where Rp = pole resistance (Q)Rc = contact resistance (s)

To eliminate Rc, select two valuesR2. These values of R will result inIt. Thus,

of R, R1 andtwo values of

IRp =It (Rc+ Rp+ R1) = It (Rc + Rp + R2) A-2

where 1t, = measured current with RI in circuitIt2 = measured current with R2 in circuit

and so, after solvingItIt

I =-IIt- It2

R - R2 1Rp

A-3

where all values of current and resistance are knownor can be measured.

APPENDIX

FIELD TESTS

Field tests were carried out to determine theproperties of 41 penta treated and untreated installedwood poles. These tests were done under fair weather,ie, 5 consecutive days of sunshine at 12C and foulweather, ie, 2 days of rain and drizzle at 12C.

- To determine the apparent resistivity and moisturecontent, the following procedure was adopted:

- for apparent resistivity P = R Aga- to determine moisture content, the apparent

resistivity was used with Equation 3 and withstandard preservative treatment penetrationdepths.