Consulting-Specifying Engineer - July 2008 - (Page 52)

Outdoor nonhazardous area Nonhazardous area Bonding locknut with a bonding jumper, threaded boss, or other listed means must be installed Service entrance switchboard Insulated Grounded Neutral bus Ground bus Bus bonded to frame Main bonding jumper Nonhazardous area Rigid metal Bonding locknut with a bonding jumper, threaded conduit boss, or other listed means must be installed Class II, Division 1 or 2 hazardous area Rigid metal conduit Outdoor transformer Primary Secondary compartment compartment X1 Grounded X2 neutral conductor X0 X3 Ground lug Grade To ground ring Motor control center Equipment grounding conductor (green wire) Ground bus External or internal bonding jumper must be installed Equipment grounding conductor bonded to ground bar Rigid metal conduit Liquidtight flexible metal conduit Liquidtight flexible metal conduit To ground electrodes Represents the equipment grounding conductor and the ground fault return path PVC conduit Equipment grounding conductor (green wire) must be pulled in conduit with phase conductors Figure 2: Hazardous grounding and bonding practices often stop as soon as the raceway leaves a hazardous environment. This is an example of what it means to continue hazardous area grounding and bonding practices back to the upsteam neutral-to-ground (shown in the service entrance switchboard) as it ensures extra safety for the entire fault path. Source: Interstates Engineering tight, flexible-metallic conduit cannot be relied on to make the required ground connection. It must be bonded with a bonding jumper, either inside or outside the flexible connection as required by Article 501.30(B), 502.30(B), and 503.30(B), respectively. The bonding jumper must be routed with the flexible raceway and should not be wrapped around the flexible connection, as this can create an inductive choke. In Class I, II, and III, Division 2 locations, there is an exception to the rule. The bonding jumper may be eliminated if the flexible connection is less than 6 ft, fittings listed for grounding are used, the protective device feeding the circuit is less than 10 amps, and the load is not used for power utilizations. A good standard to follow in all Class I and II locations (regardless of the Division) is to install the bonding jumper on the outside of the flexible raceway, because it is common for flexible connections to break or crack. This also allows maintenance personnel to quickly check the continuity of the bonding connection. Methods of grounding and bonding in both hazardous and nonhazardous areas help reduce the risk that an ignition source will exist. This is accomplished by attempting to eliminate static charge and dangerous voltage potentials between normally noncurrent metal parts of equipment and allowing the protective device to operate quickly in order to clear faults. Heinemann has been an electrical engineer for Interstates Engineering since 2005. He graduated with an electrical engineering degree from the University of Manitoba in Winnipeg, Canada, and has his EIT certification in Iowa. In his current position, Heinemann designs, specifies, and coordinates industrial electrical facilities. Vande Hoef is a senior project engineer for Interstates Engineering and has been with the company since 2002. Vande Hoef’s duties include oversight of technical design, client relationship management, and specification of electrical equipment and installation procedures. He is a licensed PE in Iowa and is a member of the Society of American Value Engineers, NFPA, and the Assn. of Energy Engineers. Additional reading • The 2005 Code Digest, Cooper Crouse-Hinds,Syracuse, N.Y. • IEEE Green book—Recommended Practice for Grounding of Industrial and Commercial Power Systems. 2007. IEEE, Los Alamitos, Calif. • NFPA 70: National Electrical Code. 2008. NFPA, Quincy, Mass. • Bossert, John A. 1986. Hazardous Locations: A Guide for the Design, Testing, Con- struction, and Installation of Equipment in Explosive Atmospheres. Canadian Standards Assn., Mississauga, Ontario. • McPartland, Joseph F. 1968. How to Design Electrical Systems. McGraw-Hill, Columbus, Ohio. • Ramhorst, Darrel. 2005. Shock-proof plan for hazardous areas. InTech with Industrial Computing, 05/01. Consulting-Specifying Engineer • JULY 2008 52

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - July 2008

Consulting-Specifying Engineer - July 2008 Contents Viewpoint Letters News M/E Roundtable 40 Under 40 Using Demand-Based Reset Strategies VFDs and Motors: Making the Right Match Grounding and Bonding Practices for Hazardous Areas Codes & Standards Case Study New Products Equipment Lifecycles Advertiser Index Green Space

Consulting-Specifying Engineer - July 2008

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