cent. Rule 245 (b) (p. 123). Fifty per cent. should be reduced to 33 per Rule 245 (e) (p. 124). Pins Note: Code permits wooden pins, which deteriorate and are not as strong as metal pins. Rule 246 (b) Table 9 (p. 125). Conductor Materials: No conductor smaller than No. 6 A.W.G. should be permitted up to 5,000 volts and none smaller than No. 4 for higher potentials. Code permits No. 8 for B and C Grades in 150-foot spans and No. 6 for higher than 5,000 volts in span of same length. Rule 247 (a) (p. 127). High Voltage Insulators: A.R.A. specifies porcelain insulators. Code permits "other material." Rule 247 (e) (p. 128). Factory Tests of High Voltage Insulators. Code gives a table of Test Voltages and the A.R.A. of FlashoverVoltages. By comparing the two tables it will be seen that the code potentials should be raised in the lower range of potentials. Section 25. Requirements for Supply Line, Including Electric Railway Feeders Rule 257 (p. 138). Wire Clearance Above Railways. (1) Code permits 22 feet at 60 deg. Fahr., which does not provide the same clearance "as under the most unfavorable conditions of loading" clause in the A.R.A. Specification, which is that due to 120 deg. Fahr. (2). Under the second condition the minimum clearance should be not less than 22 feet under the most unfavorable conditions of loading. Rule 260 (p. 139). Grades of Construction: Grade B construction should not be permitted over any part of a railway right-of-way. (See Comment under Rule 235.) Rule 263 (p. 140-141). Wire Clearances Above Rail. (a) (2). This should be not less than 30 feet for potentials over 750 volts. Rule 263 (b). No clearance of trolley wires less than 22 feet should be permitted. Specifically the 16-foot clearance herein permitted is objected to. Rule 264 (p. 142). Code clearances vary from 2 to 6 feet. Should be 8 feet for 5,000 v. A.C. and 750 v. D.C. and 4 feet for other circuits. Section 27. Supply Lines Over Signal Lines and Joint Use of Poles Rule 270 (c) (p. 145). Wire Clearance Above Signal Wires: Clearance should be increased to agree with A.R.A. Specification. Rule 272 (d) (p. 147). Special Provision Regarding Transverse Strength, Also (e) Longitudinal Stresses: These provisions should not apply to railway crossings. Rule 281 (p. 153). Transverse and Longitudinal Strength. (a) Transverse guying. (1) Medium and light loading should not be expressed as two-thirds and four-ninths of heavy loading. Their values should be stated independently. Rule 281 (a) (1) (p. 153). Heavy Transverse Loading: The last two sentences, reading: "In computing the transverse pressure on conductors, the actual number of conductors shall be used up to 10. For larger numbers of wires, only two-thirds of the total number shall be counted, with a minimum of 10, should be eliminated, because there is no engineering authority which will substantiate this method of computation. While Rule 281 gives fairly good strength at the crossing poles by providing an initial factor of safety of 2 for side-guyed poles and an initial factor of safety of 4 for unguyed poles, by neglecting one-third of the wires over 10, it will reduce the factor of safety below what should be considered good engineering. With the uncertain factors entering the problem, such as the actual strength and condition of timber poles, the unreliability of data regarding wind and ice, it seems that a factor of safety of 2, without neglecting any of the factors, is as small as should be permitted. In neglecting one-third of the wires in computing the transverse loading, the Bureau took into consideration an alleged shielding effect. After careful investigation, your Committee could find no scientific data to substantiate the shielding effect theory, and it seems that, in view of the small factor of safety of 2 generally provided for side-guyed poles, no allowance should be made on account of the shield-. ing effect of one wire upon another. Practical experience demonstrates that wires with sleet on them, when the wind is blowing hard, are not on the same plane, even if strung on the same crossarm, and they vibrate to such an extent that any appreciable shielding effect would not occur. Rule 282 (c) (p. 155). Guying in Special Cases: Side guying of poles 500 feet from crossing will be of no value in strengthening the crossing structures. Rule 284 (p. 160). Signal Line Clearances. (a) Clearance of 18 feet for tracks carrying traffic where brakemen do not ride on cars should be increased to 25 feet. (c) There should be added in the middle of this section “at loading sidings sufficient space shall be left for a driveway." Part 4. Rules to be observed in the Operation of Electrical Equipment and Lines (p. 287, Rule 400). Rule 400 states that "the employer shall furnish to each regular employe a copy of these safety rules... (or such of these rules as apply to his work), either separately or incorporated in more comprehensive rule books." Inasmuch as the rules included in the National Electrical Safety Code are of a very general nature it would be fairer to modify the provision to the effect that an equivalent of the safety rules best suited to individual needs might be used. The wording of paragraphs (a) and (b) Rule 550, page 323, is suggested. CONCLUSIONS 1. The Code purports to establish a National Standard of Safety for the users of electrical apparatus. In general the standard is satisfactory and in accordance with good practice. 2. The rules establish minimum requirements. Greater margins of safety are not prohibited. The Committee does not therefore fail to support the Code when as in the case of Part 2 it suggests greater safety provisions (p. 78, Sec. 203, note). 3. It was not the intention of the Bureau of Standards that the Code should be regarded as a designing specification. It is therefore not inconsistent that the Code be supplemented by working specifications that specify factors of safety not less than those established by the Code. Recommendations The Committee recommends that the Railroad Specifications for Electric Light, Power Supply and Trolley Lines Crossing, Steam and Electric Railways, adopted by the Association, and printed in the Proceedings, Volume 21, 1920, page 208, be opened for revision with a view to make them conform with the Code as far as consistent with established railroad standards, conferring with other interests giving special attention to the following items: (1) Definition of the Grades of Construction. (2) Minimum Overhead Clearances. (3) Clearances between Lines and between Conductors and Supports. (4) Minimum size and material of conductors. (5) Unit Stresses in Steel and Wooden Crossing Supports (Factors of Safety). (6) Grounding of Arms and Guys. (7) Grade of Construction on Branch Lines. The Committee was instructed to study and report on overhead transmission and distribution line construction for railroad use, and prepare plans and specifications for such construction, coöperating with the appropriate committees of the Signal Section and Telegraph and Telephone Section of the American Railway Association. The Committee has collected considerable data which is available for future use. The following paragraphs are presented as preliminary information and a proposed outline of policy. The Telegraph and Telephone Section of the American Railway Association has done valuable work towards standardizing pole line construction for telegraph and telephone lines. A report covering Basic Rules and Pole Tables for construction and maintenance of wood pole lines along railroads for telegraph and telephone lines was presented at the annual meeting of the Telegraph and Telephone Section of the American Railway Association in September, 1921. Your Committee issued questionnaires to about twenty representative railroads requesting information regarding railroad transmission and distribution lines at present in operation. The response to those questionnaires was not very satisfactory, but some data of interest has been collected and tabulated for the information of the Association. The subject of transmission line standards is extremely active just now. Specifications have been issued or are being considered by several state Public Utilities Commissions, and by various technical organizations. Unfortunately, however, it is not assured that these various efforts will be properly coördinated or based on a complete view of the situation. The establishment of common standards for power work and a reduction in the present number of types and kinds of line construction material is very desirable from an economic standpoint, and your Committee hopes to coöperate with other bodies to promote this result. The National Electrical Safety Code, while not providing actual specifications, nevertheless contains much data which will be of value in preparing standards. The National Electric Light Association has this year issued a very able report on transmission line construction. In that report is presented a great deal of data collected as information from member companies, regarding practices in present use. The distinction between "transmission" and "distribution" lines is not a sharp one, in fact, the characteristics often overlap. The structural problems are practically the same in both instances. A true transmission line is generally a trunk line transmitting large amounts of power over long distances at high voltage, while the distribution line transmits generally smaller amounts of power over shorter distances and at lower voltages. By far the greatest experience and development in transmission and distribution line construction has been that of the electric power companies. It seems probable that types of good construction which have proved satisfactory for them may be adequate for lines of a similar class for railroad use. However, the proximity to railroad tracks presents hazard to trains from pole and wire failures which is an important consideration. The most important difference would probably be that railroad lines are usually confined to restricted right-of-way. The railroads may properly take advantage of a cleared private right-of-way by adopting smaller overhead clearance. Railroad engineers must often adopt types of construction adapted to growth on a single line, whereas power companies may frequently develop with advantage through loops or alternative routes. A particularly unfavorable location for an outside line from the railroad point of view is that parallel to the right-of-way and immediately outside the property line. Many instances of this sort exist and in some cases there is serious conflict between such outside lines and the low voltage circuits of the railroad. Recommendations The Committee recommends that the subject be continued with a view of submitting next year Standard Transmission Line Specifications for the approval of the Association. Appendix F ITEM (7) CLEARANCES-THIRD RAIL AND OVERHEAD H. M. BASSETT, Chairman; E. J. CORRELL, Sub-Committee. The Committee communicated with an official of each electrified steam railroad; has revised the record tables and brought them up to date as shown on Statement 1, page 1, Data Regarding Third Rail Clearances, and on Statement 2, pages 1 to 6, inclusive, Data Regarding Overhead Clear ances. The Committee recommends that these tables be accepted as information and published in the Proceedings. |