Section 125.25 - Strength Requirements(1)General. Structures shall be capable of supporting, without failure or permanent set in any part, the loads specified in 220 CMR 125.24 multiplied by the following overload factors: Table 1
Type of Supporting Structure | Vertical Loads | Wind Loads | Conductor Tension |
Metal Reinforced Concrete, Sawn Timber, Laminated Wood, Guys | 1.27** | 2.54 | 1.65 |
Wood Pole-When Installed | 4.00* | 4.00* | 2.00* |
Wood Pole-At Replacement | 2.67 | 2.67 | 1.33 |
* When lines are built for a fixed period of temporary service not exceeding five years, the prescribed overload factors at installation may be decreased, provided that at no time during the life of the line will the overload factors be less than those required at replacement.
** When vertical loading contributes all or a major portion of the stress in a member, the overload factor shall be increased from 1.27 to 2.00.
For metal reinforced concrete, sawn timber or laminated wood members of structures and for guys, stresses resulting from loads specified in 220 CMR 125.64 multiplied by the appropriate overload factors specified above shall not exceed the yield or ultimate stresses, as applicable, of the particular materials.
For wood poles, including spar crossarms, bending stresses resulting from loads specified in 220 CMR 125.24 multiplied by the appropriate overload factors specified above shall not exceed the ultimate fiber stresses approved as standard by the American National Standards Institute under conditions specified in Section 4 of ANSI 05.1-1963, or latest revision thereof
All parts of structures upon which personnel can stand or climb shall be capable of supporting such weight.
(2)Corrosion Resistance. All metal parts of supporting structures, guys, anchor rods, conductors, insulators, and hardware shall be corrosion-resistant materials or shall be protected by galvanizing, painting, or other treatment which will effectively retard corrosion. Such protective covering shall be adequately maintained.(3)Metal Supporting Structures.(a)Thickness of Metal. The thickness of metal in members of metal supporting structures shall be not less than the following: Table 2
| Thickness of Main Members of Cross-Arms and Legs, In. | Thickness of Other Members, Inches |
| For localities where experience has shown rapid corrosion | 1/4 | 3/16 |
| For other localities | 3/16 | 1/8 |
(b)Slenderness Ratio of Compression Members. The slenderness ratio, L/R, of a compression member shall not exceed the following (these figures do not apply to the completed structure): Table 3
Kind of Compression Member | L/R |
Leg members | 150 |
Other members having figured stresses | 200 |
Secondary members without figured stresses | 250 |
(c)General Construction Features. Metal supporting structures, including parts of footings above ground, shall be constructed so that all exposed parts are accessible for inspection, cleaning, and painting, and so that pockets are not formed in which water can collect.(4)Wood Supporting Structures. Wood poles, sawn timber, and glued laminated timber shall be free from defects which might render them unsuitable for the intended use. Timber shall be of decay-resistant species or shall be treated with a preservative.(5)Guys. When guys are used with wood or other poles or towers capable of considerable deflection before failure, the guys can be considered as supporting the structures without deflection at points of guy attachments. When guys are used with rigid metal poles or towers incapable of considerable deflection before failure, the stresses in all parts of such structures, including guys, shall be determined giving due consideration to deformation of both structures and guys.(6)Foundations. Foundations, including guy anchors, and embedment of poles in earth shall be designed to withstand, without failure or excessive movement, loads at least 10 percent greater than those specified in 220 CMR 125.24 multiplied by appropriate overload factors given in 220 CMR 125.25(1). Due consideration shall be given to varying soil conditions, such as fluctuations in ground water levels. All portions of structures, foundations, or guy anchors subject to injurious corrosion or decay shall be suitably protected.
(7)Conductors. (a)Lightning Protection. Lightning protection wires shall be regarded in respect to loadings and strength requirements as conductors with which they are associated.(b)Sags and Tensions. Conductor sags shall be such that, under the loading, W e of 220 CMR 125.24(1), the tension of the conductor shall be not more than 60% of its ultimate strength. Also the tension at 60°F without external load, shall not exceed the following percentages of the conductor ultimate strength: Initial unloaded tension -- 35%
Final unloaded tension -- 25%
In the case of conductors having a cross-section of a generally triangular shape, such as cables composed of three wires, the final unloaded tension at 60° F. shall not exceed 30% of the ultimate strength of the conductor.
The above limitations are based on the use of recognized methods for avoiding fatigue failures by minimizing chafing and stress concentration. If such practices are not followed, lower tensions should be employed.
(c)Splices. Splices within a span shall be of such a type and so made as to have a strength and conductivity substantially equal to that of the conductor in which they are placed.(8)Suspension Insulators. Suspension insulators shall have sufficient strength to support, without failure, at least twice the loads specified in 220 CMR 125.24.(9)Conductor and Insulator Hardware. Hardware for attaching conductors and wires to insulators or to structures and for attaching insulators to structures shall support, without failure, all loads specified in 220 CMR 125.24 multiplied by an overload factor of 1.65.