A-C Resistance of Large Size Conductors in Steel Pipe or Conduit

The determination of the proper conductor size to carry a given power load on cables installed in steel conduits or pipes has been subject to assumptions which were not too satisfactory. The Insulated Power Cable Engineers Association engaged the Electrical Testing Laboratories to conduct a research project to large conductors installed in steel pipes. This paper reports the results of the research and gives suggested values of ratio of a-c to d-c resistance for conductor sizes up to 2,500,000 circular mils. It is felt that more accurate and uniform calculations of current carrying capacity of cables in conduit in air, or in pipe in the ground can be attained by use of the a-c/d-c conductor resistance ratios set forth herein, than by assumptions used previously, and therefore the data reported herein will be of benefit to both the manufacturer and the power user.