This file is raw output from pdftotext and may not be ideal for distribution. If you are a maintainer for Hackipedia, please sit down when you have time and clean this text version up. Source PDF: /mnt/main/jmc-storage/docs/SCTE/ANSI SCTE 032 Ampacity of Coaxial Telecommunications Cables (2009).pdf Like all conversions the text below should be fully readable as UTF-8 unicode text. --------------------------------------------------------------- ENGINEERING COMMITTEE Interface Practices Subcommittee AMERICAN NATIONAL STANDARD ANSI/SCTE 32 2009 Ampacity of Coaxial Telecommunications Cables NOTICE The Society of Cable Telecommunications Engineers (SCTE) Standards and Recommended Practices are intended to serve the public interest by providing specifications, test methods and procedures which promote uniformity of product, interchangeability and ultimately the long term reliability of broadband communications facilities. These documents shall not be in any way preclude any member or nonmember of SCTE from manufacturing or selling products not conforming to such documents, or shall the existence of such practices preclude their voluntary use by those other than SCTE members, whether used domestically or internationally. SCTE assumes no obligations or liability whatsoever to any party who may adopt the Standards or Recommended Practices. Such adopting party assumes all risks associated with adoption of these Standards or Recommended Practices, and accepts full responsibility for any damages and/or claims arising from the adoption of such Standards or Recommended Practices. Attention is called to the possibility that implementation of this standard may require use of subject matter covered by patent rights. By publication of this standard, no position is taken with respect to the existence or validity of any patent rights in connection therewith. SCTE shall not be responsible for identifying patent for which a license may be required or for conducting inquires into the legal validity or scope of those patents that are brought to its attention. All Rights Reserved © Society of Cable Telecommunications Engineers, Inc. 2009 140 Philips Road Exton, PA 19341 i Table of Contents 1.0 Scope 1 2.0 Ampacity Reference Tables 2 3.0 Engineering Supervision 4 4.0 References 5 ii 1.0 SCOPE This document provides the current carrying capacity or AMPACITY of coaxial cables used in the Telecommunications industry. The method used to calculate the tabulated ampacities is a thermodynamic model of a cable installed indoors in air and considers the heat flow from the inner and outer conductor through the dielectric and jacket materials. It assumes that the conductors carrying current reach an operating temperature of 65°C based on the cables ability to dissipate heat. This temperature was chosen to substantially minimize the possibility of accelerated thermal aging of the dielectric and jacket materials. System designers are encouraged to consider the effect of this operating temperature on conductor resistance (R), voltage drop (IR) and power consumption (I2R). The National Electric Code (NEC) considers the most convenient and expeditious method of defining the ampacity of cables to be through the use of tables. The tabular format included in this document illustrates the ampacity of trunk, distribution and drop type coaxial cables commonly used in the Telecommunications industry. This procedure shall not be used to determine ground conductor size as referenced in NEC Article 810, 820 or 830 as applicable. The ampacity provided for trunk and distribution coaxial cables are for copper-clad aluminum center conductors and solid (smooth wall) aluminum outer conductors. Drop coaxial cable ampacity relate to cables with a copper-clad steel center conductor and a combination of aluminum tape(s) and braid(s), which represent the outer conductor. 1 2.0 Ampacity Reference Tables Table 1: Trunk and Distribution Cable Ampacity (Amperes) Current in Both Conductors Cable Series 20°C (68°F) 40°C (104°F) Ambient Ambient 412-F 33 25 440-D 41 31 500-F 43 32 500-D 49 36 540-F 50 37 565-F 50 38 625-F 54 40 650-D 64 48 700-F 66 49 715-F 68 51 750-F 67 50 750-D 79 59 840-F 79 59 860-F 84 62 875-F 81 60 1000-F 94 71 1000-D 108 80 1125-F 112 83 1160-F 117 87 F=FOAM, D=DISC & AIR 2 Table 2 Drop Cable Ampacity (Amperes) Current in Both Conductors Cable Series 20°C (68°F) 40°C (104°F) Ambient Ambient 59 Series Tape & Braid 6 4 Tri-Shield 6 4 Quad-Shield 6 5 6 Series Tape & Braid 8 6 Tri-Shield 8 6 Quad-Shield (Braid) 8 6 7 Series Tape & Braid 10 7 Tri-Shield (Braid) 10 8 Quad-Shield (Braid) 10 8 11 Series Tape & Braid 13 10 Tri-Shield 13 10 Quad-Shield 13 10 3 3.0 Engineering Supervision When calculating the ampacity of coaxial cables the worst case condition is typically considered. Since indoor cables do not benefit from cooling from wind, it is assumed cables installed indoors or in enclosed areas represent the worst case scenario. Under engineering supervision and guidance, ampacities for coaxial cables can be calculated by solving the following simultaneous equations: tc − ts I= (Ric − Reoc ) ∗ (Rth ) and 0.182 ∗ ε ∗ D ∗ (t s − ta ) + 0.0714 ∗ D 0.75 ∗ (t s − ta ) 1.25 I= (Ric − Reoc ) ∗ (n ) The ampacities calculated from these general equations are considered to represent current flowing in both the center and outer conductors of a coaxial cable. In the provided equations, Reoc is the effective increase in center conductor resistance due to the effects of the outer conductor and is calculated as follows: Rth − Ri Reoc = ∗ Roc Rth Rth is the total thermal resistance to heat flow from the center conductor to the ambient air and is calculated by summing the insulation and jacket thermal resistance. The metallic components of the cable construction are considered to be isotherms and therefore disregarded. Rth = Ri + R j Where C Ri = 0.00522 * ρ i * ln d and D R j = 0.00522 * ρ j * ln Ds 4 The variables used in the previous equations are defined as follows: I = Ampacity (Amperes) tc = Conductor operating temperature (°C) ta = Ambient temperature (°C) ts = Cable surface temperature (°C) Ric = Inner conductor resistance (Ω/ft at tc) Roc = Outer conductor resistance (Ω/ft at tc) Reoc = Increase in Ric due to outer conductor Rth = Total thermal resistance of circuit (°C/watt/ft) Ri = Thermal resistance of dielectric (°C/watt/ft) Rj = Thermal resistance of jacket (°C/watt/ft) ε= Surface emissivity (jacketed=0.95, bare=0.35) ρi = Thermal resistivity of the dielectric material = 1300 °C/watt/ft for both foam and disc & air dielectrics ρj = Thermal resistivity of the jacket material = 400 °C/watt/ft for polyethylene (PE) jackets = 350 °C/watt/ft for polyvinylchloride (PVC) jackets ln = Natural logarithm n = Number of cables d = Center conductor diameter (inches) C = Insulation diameter (inches) Ds = Outer conductor diameter (inches) D = Jacket diameter (inches) 4.0 References: TFC Technical Note 1075, Alan J. Amato, Times Fiber Communications. The National Electric Code Handbook. The Calculation of the Temperature Rise and Load Capability of Cable, J.H. Neher and M.H. McGrath, AIEE, March 1957. The Current Carrying Capacity of Rubber Insulated Conductors, S.J. Rosch, AIEE, 4/38. 5