IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 47, NO. 2, MARCH/APRIL 2011 989 To Bond or Not to Bond: That is the Questio Massimo Mitolo, Senior Member, IEEE, Fabio Freschi, and Michele Tartaglia, Senior Member Abstract—The bonding of electrical equipment plays a crucial role in maintaining the same potential between conductive parts likely to be energized and conductive parts liable to introduce a “zero” potential into the premises. Voltage rises between such parts are unsafe, as they may induce harmful currents through the human body, the magnitude of which may vary depending on a number of factors. This paper seeks to clarify the bond- ing requirements in low-voltage electrical systems, by using the concepts of exposed conductive parts and extraneous conductive parts, present in the International Electrotechnical Commission standards, applied to a proposed electric shock model of the human being. With the purpose of reducing the consequences of electric contacts, the authors propose objective criteria to decide whether conductive “dead” objects and enclosures of electrical equipment must be bonded or not. Index Terms—AC current, body impedance, bonding, electric shock model, exposed conductive part, extraneous conductive part (EXCP), heart-current factor, resistance to ground, shock voltage, shoes. N OMENCLATURE Z BH−BF Total body impedance for the both-hands-to-both- feet pathway. Z M H−T Hand-to-trunk body impedance (medium surface area of contact). Z L T −F Trunk-to-foot body impedance (large surface area of contact). Z M H−H Hand-to-hand body impedance (medium surface area of contact). Z L H−F Hand-to-foot body impedance (large surface area of contact). Z L H−T Hand-to-trunk body impedance (large surface area of contact). I. INTRODUCTION N OT all the conductive parts in electrical systems must be bonded for safety purposes. We can basically classify such parts as follows: 1) conductivepartsnormally live(e.g.,line conductors and/or busways); Manuscript received May 18, 2010;revised August 11, 2010;accepted October 18, 2010. Date of publication January 6, 2011; date of current version March 18, 2011.Paper 2010-PSEC-150.R1, presented at the 2010 Industry Applications Society Annual Meeting Houston, TX, October 3–7, and approved for publication in the IEEE T RANSACTIONS ONINDUSTRY APPLICATIONS by the Power System Engineering Committee of the IEEE Industry Applica- tions Society. M. Mitolo is with Chu & Gassman, Middlesex, NJ 08846 USA (e-mail: mmitolo@chugassman.com). F. Freschi and M.Tartaglia are with the Dipartimento Ingegneria Elet- trica, Politecnico di Torino, 10129 Turin, Italy (e-mail: fabio.freschi@polito.it; michele.tartaglia@polito.it). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIA.2010.2103543 2) conductive enclosures of electrical equipment, normally not live but likely to become live when their basic insu tion fails, which can be touched; 3) conductive enclosures of electrical equipment, normally not live but likely to become live when their basic insu tion fails, which cannot be touched; 4) conductive parts not forming part of the electrical in- stallation that are liable to introduce an electric poten (generally, the earth potential) into the premises; 5) conductive part of electrical equipment, which can only become live through contact with an exposed conduct part (ECP), which has become live; 6) conductive parts not previously mentioned. Once properly identified in the electrical systems, only the conductive parts 2 and 4 shall be bonded, as examined in the next sections. The aforementioned classification of conductive parts is in harmony with all the chapters of the International Elec- trotechnical Commission (IEC) 60368 “Electrical installati of buildings,” which is currently the applicable IEC technic standard for low-voltage systems. 1 II. EXPOSED CONDUCTIVE P ARTS Reference [1] definesconductive enclosures of electrical equipment as ECPs. The definition of ECP contains the foll ing stipulations. 1) ECPs must form part of the electrical equipment and c be touched (even if out of reach). ECPs are not live but likely to become live when their basic insulation fails. 2) A conductive part of the electrical equipment, which c only become live through contact with an ECP, which become live, is not considered an ECP [2]. References [3] and [4] prescribe that ECPs be connected the same earthing system individually, in groups, or collec via a protective conductor [protective earth (PE)], also refe to as an equipment grounding conductor. To provide an interpretation to the aforementioned defin the authors propose the following examples. A. Class I Equipment in Contact With Conductive Supports In Fig. 1, an ECP is diagrammatically shown. The ECP ha the basic insulation, which is the insulation applied to its live 1 IEC 60368 delineates the fundamental concepts of protection for the s of persons in low-voltage systems (not exceeding 1 kV), which include pro- tection against electric shock, protection against thermal effects, protection against overcurrent, protection against faultcurrents, and protection against overvoltages. 0093-9994/$26.00 © 2011 IEEE