Electrical Wooden Poles Maintenance and Inspection
Wood poles are the most commonly used method of supporting distribution overhead
line conductors for the electricity supply industry. Periodic and thorough inspections of
wood poles are vital for maximizing service life and determining requirements for repair, modification or upgrading. Inspections provide knowledge of the component, loadings to which it is subjected, quality of materials involved, condition, and effectiveness of fasteners and other hardware. All must be known in order to evaluate the ability of a structure or its components to perform its intended function, and to determine necessary maintenance procedures for improving performance.
Poles exposed to wetting can decay when water remains in contact with them or when rapid drying is restricted. Steel support sleeve slacking base drain hole is a good example. Periodic pretreatment of such poles will significantly increase service life. Decay can typically be found where seasoning checks or bolt holes have exposed untreated wood found beneath the treated shell. Openings may result from deep seasoning checks, from gouging by pointed tools, from loosened fastenings such as bolts, or when cuts or holes made after treatment are left unprotected. That is why it is vitally important to treat with preservatives, all areas that are exposed to probing, cutting or drilling. Periodic pretreatment of areas prone to moisture contact and accumulation must also be done on a scheduled basis.
Electrical Wooden Poles References
Industry Codes and Standards
American National Standards Institute
ANSI 05.1 Wood Poles – Specifications and Dimensions
American Society for Testing and Materials
ASTM D4442 Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
American Wood Preservers Association
AWPA C1 All Timber Products-Preservative Treatment by Pressure Processes
AWPA C4 Poles–Preservative Treatment by Pressure Processes
AWPA M1 Standard for the Purchase of Treated Wood Products
AWPA M2 Standard for Inspection of Treated Timber Products
AWPA M4 Standard for the Care of Preservative-Treated Wood Products
AWPA P1 Standard for Coal Tar Creosote for Land and Fresh Water Use
Wood Pole Natural Defects and Limitations
Checks
Checks are openings in the surface of the pole that are formed when the wood dries and shrinks. Checks penetrate the wood but do not go through to another Checks have no significant effect on the strength of the pole and are not limited by the specification.
Splits
Splits are similar to checks but penetrate completely through the pole. Splits almost always occur on the ends of the pole and can occur as a result of mechanical damage as well as drying. Splits can form when checks join and divide the end of the pole into two or more parts completely separated from each other. Splits in the top and butt of a pole are limited by the distance down the length of the pole that they can be traced continuously. In the top, the split can be caused for rejection when it goes down the pole more than one foot from both sides. In the butt, the split can go no more than two feet up both sides of the pole.
Knots
A knot on the pole is where a branch grew out of tree. Knots are measured in the direction around the pole at right angles to the direction of the length of the pole. The ANSI specification limits the amount of knot diameters in any one foot section of the pole. If the length of the pole is 50 foot long, the total of all the knot diameters can not be more than ten (10) inches. If the pole is less than 50 foot long, the total of the knot diameters can not be more than eight (8) inches. Knots one half inch diameter or less are not counted.
Decay
Decay is caused by a group of plants called fungi. Fungi are very small and are invisible. As fungi grow in the pole, they eat the wood and by the time damage becomes visible as decay, a great amount of damage has been done in the infected area and the wood has lost its strength. Decayed wood is usually soft and breaks easily when mashed or twisted. Only one type of decay is allowed in Southern Pine and Douglas Fir. This is decay in knots that does not go into the body of the pole outside the knot. Knots that show decay is half or less of their surface are almost always ok however, knots that show most or all their surface
being decayed and the decay going deep into the knot (2 inches or more) are the type that should be checked.
Shakes
A shake is a separation between growth rings in the butt or top caused by drying. It appears as a ring and can go part of the way or all the way around the end of the pole. In the top of the pole, a shake is acceptable if the distance across it is not more than one half the distance across the top. In the butt, a shake is allowed within two inches from the edge if it does not go more than two feet up the pole and the opening of the shake is not more than 1/8 inch wide. If the shake is more than two inches from the edge, it can not go past the ground line area and can be more than 1/8 inch wide.
Spiral Grain
Spiral Grain is the result of the wood grain growing at an angle instead of straight up the tree. As the wood dries and checks develop, where spiral grain is present, the checks will follow the angle of the grain and will circle around the pole as they are traced up the pole. For poles 30 foot or shorter, the grain can not circle completely around the pole more than once in ten foot of pole length. For poles 35-45 foot, only one circle in 16 foot of pole length is allowed; for poles 50 foot or longer, one full circle in 20 foot of pole length is the limit.
Wooden Pole Inspection and Maintenance Procedures
Inspection & Maintenance Procedures for Wood Poles
Internal Decay
When performing inspections and maintenance on distribution poles it is important to know that internal decay occurs as a result of fungal infestation:
(1) Start in poles before treatment or
(2) Where wood destroying organisms are able to penetrate the outer protective shell of preservative treated wood which surrounds the non-treated wood in the center.
Deep checks which develop after treatment, mechanical damage from improper handling, woodpecker holes or other actions which break the protective shell, provide avenues for entry of decay fungi. Internal decay will also develop in pole tops cut or holes bored in the field when the cut surface is not coated with a topical preservative.
External Surface Decay
External decay is most common at or below the ground lime. As poles age, external decay may develop as the effectiveness of the treatment begins to decline.
Insects
Attacks of the untreated interior portions of poles by subterranean termites or carpenter ants are difficult to detect. However, if insects can gain entry, so can decay fungi. Therefore, the two will often occur together.
Electrical Wooden Poles Inspection Procedures
The purpose of a pole inspection is to:
(1) Identify poles that are dangerous and should be replaced and
(2) Identify poles which are in the early stages of deterioration so that corrective actions can be taken.
Visual: A visual examination of the poles, using binoculars to inspect tops, can provide valuable information regarding the pole’s condition.Â
Decay: Machine-damaged areas and checks should be critically examined during visual inspection. The size and location of seasoning checks should be noted. In general, the wider the check, the deeper it penetrates and the more likely untreated heartwood is exposed.
Remember, only decay in the advanced stages is readily apparent. The presence of fungi in wood where decay has not progressed appreciably can be detected only by culturing or microscopic examination of the wood. Early decay can extend four feet or more above internal, visibly rotten areas in Douglas-fir poles. Surface decay usually occurs within
the first 12 to 18 inches below the ground line, so digging is generally necessary to detect it. Periodic application of groundline preservativetreatments will prevent and/or control this type of decay.
Termites and Carpenter Ants: These insects infest the internal untreated portion of poles. Therefore, little external visual evidence of their presence is apparent. Some termite galleries may be present if the insects are trying to bridge over treated wood. In addition, if a carpenter ant infestation has occurred, scattered bits of very fibrous and sawdustlike frass may be present in the area. Since a break in the protective shell must occur before these insects can reach and infest the untreated wood, decay is also likely to be present.
Vertebrate Organisms: Damage from vertebrate organisms, such as woodpeckers, is usually apparent. Binoculars should be used when inspecting large poles. If the damage is fresh, broken pieces of wood from the excavated hole should be present on the ground. Decay will be associated with older damage.
Mechanical: Mechanical damage is generally obvious and found in the ground line area to a few feet above the ground.
Physical Tests: In addition to visual inspection, several physical tests are available to aid pole inspectors in determining the presence of biological damage. Some of these methods are very basic while others involve sophisticated electronic equipment. In all cases, considerable experience is required to interpret the results, especially with the newest
nondestructive testing devices for wood poles.
Sounding: Sounding is a common method of inspecting poles for internal voids. The pole is firmly hit with a hammer from ground level to as high as one can reach. A crisp sound usually indicates the pole is solid. A dull sound thus indicates wet and possibly rotten wood and a “drum” sound indicates a void. To develop experience, poles that are sounded should then be bored to confirm which defects are actually present.
Boring: Where decay or insect attack is suspected, the pole is generally bored for confirmation. Increment borers are most commonly used. The core can be closely examined at the site and also saved for later culturing or microscopic examination. An effective, but simple way to save increment cores is to insert them into soda “straws”, seal the ends
and label for identification. Protected in this manner, increment cores can be shipped to a laboratory for biological studies.
Poles that sound suspicious should be bored near deep checks and at the pole base or at ground line. If rot is detected, the poles should be bored at three or four points around the circumference. The shell thickness, depth of preservative treatment, and pole circumference are determined. Requirements for replacement, reinforcement, field treatments or schedules for reinspection can then be determined.
When boring holes above ground, the tool should be oriented slightly upward. This prevents water from accumulating in the hole. All openings made during inspection should be treated with a registered preservative and plugged with preservative-treated dowels. Protective
goggles and other safety equipment, as appropriate, should be worn.
Biological Tests: It is important to detect and treat decay fungi as early as possible if the strength properties of the wood are to be maintained. Biological tests are still the most reliable means for detecting early stages of decay.
Shell Thickness Indicator: A shell thickness indicator can be used to determine the thickness of the non-decayed wood when poles are drilled rather than using an increment borer. The rod is inserted into the hole and then pulled back with pressure against the side of the hole. The hook at the end will catch on the remaining sound wood. When pushing a tight fitting shell-thickness indicator into a hole, you can feel the tip of the hook pass from one growth ring to another in solid wood, but not in rotten wood.
Culturing: The early or “invisible” stages of decay can be detected by culturing in the laboratory the core samples you have collected in the field using increment borers. Each core is placed in a plastic straw, labeled and the ends of the straw stapled shut. The cores are brought to the laboratory and culturing begins within 24 hours.
Insect Identification: It is usually beneficial to identify insects if an infestation has occurred. If field identification is not possible collect the insect, their boring dust (frass), and a portion of the wood with typical damage, and consult the cognizant Pest Management Consultant (See Appendix A) for assistance with identification.
Determination of Serviceability: The results of your visual and physical inspections and lab reports help you determine the serviceability of the wood member. As the integrity of a wood member is destroyed by biological agents, its ability to withstand the load it was designed for is diminished. As more and more wood is destroyed, the structure becomes
weaker. With poles, the location of the wood that is destroyed is more important than the amount of wood destroyed. The outer 44% of the pole radius contributes most (about 80%) of the bending strength.
Therefore, decay in the center of the pole will reduce strength substantially less than if the outer shell is deteriorated. Decay in the above ground portions of the outer shell of a well-treated pole is an indication that the pole was decayed before treatment. This is why it is
important to specify “white wood” inspection of treated products to be purchased.
Remedial Treatments
Superficial Preservative Treatments
Preservative applications by brush, spray or pinstream (oil squirt can) do not penetrate deeply into the wood. These treatments are therefore not intended to protect the wood from sustained exposure to degrading organisms but more so as an adjunct to a good initial pressure preservative treatment. Brush treatments should be flooded onto the surface and not brushed out thin, like paint. Checks and other openings should be saturated to the point of refusal. A pinstream application using a squirt type oil can applicator can be used effectively in this type of application. Wood should be well dried before treatment or it will not accept preservatives applied in this manner. If spraying, a course spray should be used to minimize health hazards. Special precautions should be taken to avoid drift. Topical treatments recommendations for the major preservative classes are as follows:
Oil borne Preservatives. At least two brush applications of either creosote or a solution of at least 5% pentachlorophenol in a suitable solvent or one heavy application of a grease/paste containing at least 10% pentachlorophenol. Cleanliness requirements should dictate the type of treatment.
Water borne Preservatives. At least one application of a 5% solution of the same preservative used in the original treatment. For either of the above preservatives, appropriate copper napthenate solutions can be utilized as this preservative is compatible with either of the above preservative formulations.
 Ground line or Bandage Treatment
Ground line brush or bandage treatments are very effective in controlling surface decay in the outer shell of poles at and below ground line. With these treatments, the soil is excavated from the bases of poles to a depth of approximately two feet. The exposed surfaces of poles then are checked for decay and, if present, the decayed wood is removed using a sharpened shovel.
Next a bandage wrap containing a preservative is fastened around the below grade portions of the poles or preservative is applied directly to the pole surface and covered with a water-impervious wrap such as polyethylene that is fastened tightly to the poles. The wrap should not be damaged as the backfill is being replaced. Before treatment, the surface to be treated should be cleaned of any decayed or loose wood. No more sound wood than necessary should be removed. All debris should be removed from the excavated area around the pole.
Internal Void Treatment
Liquid preservatives or fumigants may be used to control decay and insect attack within the central core of poles. These treatments require drilling holes into the decayed areas and placing the preservatives or fumigants in the holes. The holes are plugged following treatment. Internal void treatment with liquids is most successful on cedar and other woods that develop well defined rot pockets and where the transition from rotten to sound wood is abrupt; they are least effective in Douglas-fir with poorly defined rot pockets.
For Douglas-fir, use a fumigant alone or in combination with a water-soluble preservative solution. To arrest internal decay, water-soluble chemicals, e.g.,arsenicals, fluorides or borates are forced into the voids and diffused through the wet wood. Ants in pole voids can be controlled by injection with volatile liquids combined with preservatives such as creosote or pentachlorophenol.
Poles shall be bored with a 3/8 inch drill bit, a sufficient number of times to assure uniform
internal coverage. Preservatives are pumped into the bottom hole until it runs
out the next higher hole. The hole is then plugged with a preservative-treated
plug, and preservative is then pumped into the next higher hole until it runs out
the hole above. This procedure is repeated until the entire cavity is flooded or a
maximum of one gallon of preservative is used. Preservative pastes also can be
injected into holes to treat internal voids.
Fumigant Treatment
Fumigants can control internal decay for at least nine years. As a result, the use
of fumigants is now common technology. Sodium N-methyl dithiocarbamate
(Vapam), methylisothiocyanate (MITC-Fume) (Vorlex), and
tricholoronitromethane (chloropicrin) are currently registered with the U.S.
Environmental Protection Agency (EPA) for application to wood. These are
restricted use pesticides and can only be applied by a certified applicator. Label
directions for applications of individual fumigants must be followed. In general,
starting at the ground line, 5/8 to 7/8 inch diameter holes are drilled directly
towards the center of the pole at a steep downward angle. The hole should not
be through the pole or intersect seasoning checks which would allow the
fumigant to escape. To assure good distribution of the fumigant, holes are
spaced evenly (and drilled in a downward direction) around the pole in an
upward spiral pattern with a vertical spacing of 6 to 12 inches. If more than two
treating holes intersect an internal void or decay pocket, re-drill the holes further
up the pole into relatively solid wood where the fumigant will gradually
volatilize and move through the wood.
Pole Top Protection
Pole top deterioration is caused by decay fungus and weathering action. Depressions,
splits, and checks create water holding pockets which cause wood to expand and
contract freeze and thaw and subsequently split and check. These conditions present an
ideal condition for decay fungi. When left unchecked, the pole top continues to
deteriorate until pole topping or removal is necessitated. Pole top products are now
available which effectively protect pole tops from weathering. Decay fungi and
ultimately degradation.
Pole tops (caps) are designed to keep the roof portion of poles free of moisture thus
preventing attack by decay fungi. Preservative fluids are also available which should be
applied to the pole tops prior to capping or topping.
Pole Strength Restoration
Carpenter ants, decay fungi and termites can cause extensive damage to wood poles.
Left unheeded they can cause serious damage and result in early pole failure. When poles are found to be structurally damaged and accompanied by significant strength loss, repair alternatives versus replacement must always be considered. New state-of the-art techniques, using epoxy resins, fibers, and fillers can restore poles to their original strength. When cured, these epoxies are stronger than wood and can also be drilled, sanded, painted or sawn and be applied to wet surfaces. When applied in conjunction with preservative supplements for preventing further deterioration, poles can be restored to original condition. When site conditions make pole replacement prohibitively costly, pole restoration can become a viable solution via cost reduction and prevention of down time. Therefore, this should become an available procedure in any pole maintenance program.
Pole Performance Evaluation (In-Service)
Wood inspection surveys conducted at several sites around the world determined that
many poles are performing extremely well, even in the most hostile environments.
Preservative assays were conducted at these sites. Surprisingly, retention assays for
these poles (all creosote preservative treated) indicated exceptionally high retention
levels. Keeping in mind also that many of these poles have been in service for over
25 years during which time some preservative leaching has occurred. The exceptional
performance being experienced can be primarily attributed to superior original
preservative treatment. In order to continue this exceptional performance, preservative
treatments found in these poles should be duplicated when ordering new replacement
poles.