Crossarms for Open Wire Construction
We begin this section with a discussion of cross arm assemblies (whether wooden or metallic) for open wire construction.
Depending upon the mill or lumber company manufacturing cross arms, the composition and treatment varied widely. Many organizations who were buyers specified a species of wood and type of preservation for their larger orders. Other utilities, telephone companies and railways’ purchasing was guided by a national standard, such as NELA (NEMA), the ARA (American Railroad Association’s Communications Section), the REA (Rural Electrification Administration), Bell System (AT&T practices and recommendations) as well as Independent Telephone Associations which statewide or regional requirements were served.
For example, if we take a Midwestern supplier, such as Hughes Brothers of Seward, Nebraska, an early supplier of cross arm assemblies for utilities and telephone companies, their wood composition was Washington Fir. Quoting from their late 1930s catalogue pertinent to the period in which open wire arms were sold widely:
“Hughes Washington Fir Cross Arms are made of selected, old growth, yellow fir which gives them greater durability and density, with unusual strength and light weight. Washington Fir may be considered as Douglas Fir, but all Douglas Fir is not Washington Fir. Douglas Fir is the common name given to all species of fir grown in the Coast Region, west of the Cascade Mountains, the Rocky Mountain Region, and the Intermountain Region. Douglas Fir, in general, is red or yellow in color, according to the rapidity or slowness of its growth. Fast growth wood is usually reddish in color. Slow and old growth wood is usually yellow and it is this which is selected for Hughes Washington Fir Cross Arms. Durability in wood is largely a matter of percentage of heartwood. Hughes Washington Fir Cross Arms, cut from logs that have uniformly a very thin sap ring, are practically all heartwood. This is one of its greatest advantages giving uniform durability in all sizes. Hughes Washington Fir Cross Arms have the innards to withstand the rigors of climatic changes, and are giving a satisfactory record of performance over a long period of years in all sections of this country , and even farther, in various sections of the world. For exposed use it is recommended that material of close grain be selected in order to minimize checking and insure durability.”
From a 1931 Hughes Brothers Catalog [Number Eleven, 1931] of Transmission, Distribution, Substation and Special Applications Products.
From a General Electric Supply Company catalogue published in the late 1920s, are the standard specifications for wooden cross arms. Both electric distribution and transmission as well as open wire signal and communications types are listed. The National Electric Light Association (NELA) would become NEMA (The National Electrical Manufacturers Association) in the mid-1930s. Typically, the pins, braces, bolts, and other accessories were furnished independently of the cross arm orders. However, several manufacturers did furnish fully equipped wooden pins integral with the cross arm orders. This was primarily with telecom and signal circuit arms (for railroad use). Steel pin equipped arms were not furnished as a unit. Steel pins would be purchased separately and installed by the user.
There were several types of wooden cross arm assemblies.
2A – Two pin Arm
2A – One pair of wires with spans up to 600 feet in length. Typically, these arms would support two dead-end C-brackets. A notch was cut into the arm so that the arm would not rock back and forth on the round pole. The 5/8″ or smaller carriage bolt would be used to attach the arm to the pole. One advantage of this arm was that no steel or wooden brace was needed on tangent sections of line. The framing (notch) would prevent tilting of the arm. At transposition points however, a 20″ span steel brace was required to offset the weight of the bracket. REA/RUS would allow the arm to be mounted longitudinally instead of transversely, so that two transposition insulators might be inserted on pins and for the actual arm to serve as the transposition bracket instead of mounting a separate carriage bolt and steel point type bracket on the offset arm. Also, this type of arm was used primarily on REA construction as a dead-end with two-pin side arms. Bell, GTE, Independents used wooden side bracket construction. Typically, this was the case where it was not expected that the line would be increased in size by adding further pairs on existing facilities.
This small four pin arm was approximately four foot long and was supported by a single 20″ span brace and 5/8″ bolt. Wooden pins were typically furnished integral to the unit. Many times, a notch was cut into the arm in order to frame it for the pole. This unit was sometimes used as a transposition element with a four wire party line lead or service station lead. Occasionally, it was added to an existing lead, to support nearby farm party lines, as an underbuild to joint use exchange or toll leads.
The Carrier Types of Crossarms – S and W
Both of these arms were similar in all respects except for the type of pins (wooden locust or steel) installed on the arms. These were unique as they did not include “pole pairs” and separation between the inside pairs was 30″ instead of the standard 10-pin’s 16″ separation of pole pairs. Steel braces were 30″ span type and secured with 1/4th” carriage bolts. Ten foot long with all holes bored as ordered from the manufacturer. Again, the steel pin type (S-8) were not integrally equipped; separate orders were necessary for both the pins and arms. However, some manufacturers did equip their W-8 arms with wooden pins already installed. The separation between the pairs on each side of the arm was 26 inches. The pairs were eight inch spaced between insulator pins. The distance between span brace attachment points on the arm were 21 1/2 inches.
Wooden pin W-8 arms were bored for 1 1/4″ pin holes. Steel pin (S-8) arms were bored for 11/16″ pin sizes.
Six Pin Arms
These were 6′ long arms with wooden pins primarily equipped. Three pins on each side of the pole center. Two twenty-inch crossarm span braces were used to offset tilt on either side of the installed arm. 3/8″ x 4″ carriage bolt was used to secure the brace. The bottom intersecting common hole securing the two braces to the pole was 9/16ths inch in diameter. A lag screw would be attached at this point.
Type “N” Arm
Type N arm was used where narrow right of way considerations were an issue. While it was primarily equipped with wooden pins, the length of the arm was two feet shorter in its overall length and separation between the pins was 8″. 20″ braces on either side of the arm supported the weight of the ten conductors. I have seen these used by CONTEL in Iowa as a standard tangent arm. Unusual to see, but were used outside of unique circumstances were it was used more as an “exception” rather than a “rule.”
Type 10A/10B Arm
We have spoken about this common telephone asset previously in other areas of this website, but it is seen most often in open wire construction where multi-pair exchange and toll use dominates construction. These ten foot arms can be equipped with either eight or ten pins. Nearly all specified by either commercial communication and railway/transportation companies are of the ten pin variety. Steel pins with wooden cobs can be used or wooden locust/oak pins can be also equipped on this arm. The braces required to equalize load stresses on this type of arm are two 30″ span braces. Occasionally, a 10B arm can be modified to add a further pole pair, owing to the ten (or eleven, depending upon ownership) inches between pins, composing a 12-pin arm. These are rare, but have been seen. Geddes, South Dakota had a working 12-pin arm lead prior to 1972. 10A arms had 16″ separation between the pole pairs. A 10B arm had 18″ separation between the pole pairs.
Type 16A Crossarm
The 16A was a unique feature in the open wire landscape. Supported by two 30″ span steel braces, the unit was 10′ foot long with 4″ between each pin making up a total of eight pins on either side of the arm. This tight spacing was required in special circumstances of right of way and special span construction. In my many years of witnessing open wire construction, I have only seen 16A arms several times in my life. They are definitely unique. In January 1979, the manufacturers discontinued this type of crossarm.