CODE FILEBY LES STOCH, P.ENG.Grounding basics<strong>Electrical</strong> system grounding is not widely understood,which is why the subject can lead to many differentdiscussions, interpretations and a variety of philosophies.This article is just such a discussion, as it reviewssome of the electrical system grounding requirementsspelled out in the Canadian <strong>Electrical</strong> Code (and throwsin a few curve balls to keep things interesting).Rule 10-106 requires that alternating current systemsmust always be grounded when their voltage-to-groundis 150 volts-to-ground or less, or when the electrical systemhas a neutral conductor. In general, this requirementapplies to both 120V/208V and 120V/240V systems.Rule 10-204 tells us that neutral connections to groundmust be made at the main service equipment and again atthe transformer that supplies the utilization voltage. Butthe rule specifies there must be no neutral connections toground anywhere in the electrical system past the mainservice equipment (see Figures 1 and 2). So, when thereis bonding between the cases of electrical equipment andthe system neutral downstream from the main electricalservice, it must be removed.You might be justified in asking why the code prohibitsall interconnections between the electrical system neutraland the cases of the equipment downstream from the mainelectrical service. Two good reasons come to mind:1. an inadvertent parallel return path for load currents iscreated when the neutral becomes grounded anywherepast the grounding point at the main service; and2. when the main electrical service has ground faultprotection of the zero sequence or residually connectedtypes, grounding the neutral downstreamfrom the fault-sensing equipment effectively disablesthe ground fault protection.I’m sure none of this is news to you, but how can unintentionalgrounding show up in your electrical systemTransformerGroundingFigure 1Figure 2NeutralNeutralEquipmentCase BondingEquipmentCase BondingMain Servicethat violates the code and create the problems discussed?An emergency standby generator could be one way. Theframes of some generators are bonded to the generatorneutral. This information should be noted somewhere onthe machine. Connecting this type of standby generatorto an electrical system creates an unintended downstreamground point. A four-pole transfer switch is then requiredto ensure this doesn’t become a problem, as it ensures thegenerator neutral is disconnected at all times when themachine is not in operation.Another way that an unplanned downstream ground canshow up is through the installation of electrical equipment,such as a panelboard, that has a bonding screw/jumperconnecting its neutral bar to the case of the equipment.These should always be removed to avoid accidental downstreamgrounding.There is, however, one exception to this rule: Rule10-208 specifies that when two or more buildings are suppliedfrom a single service, either:NMain Service GroundingMain ServiceNMain Service GroundingBoundingPanel• the service neutral may be grounded at each ofthe buildings; or• the system neutral is grounded only at the mainelectrical service.A common example is when a building is supplied as afeeder from another building. Here, the neutral may begrounded at the service entrance of each building, but theremust be no bonding conductor between the two buildings,since the service equipment is already bonded to the systemneutral in each building. Adding bonding between the twocreates a parallel neutral conductor. (You should note thatthis is the only grounding arrangement permitted by thecode when the second building contains livestock).A second grounding arrangement is also permitted.In this scheme, the system neutral is grounded only atthe main service in the first building. The case of serviceequipment in the second building must not be bonded tothe neutral, since it creates an additional grounding point.However, a bonding conductor must be installed betweenservices in the two buildings, otherwise there would be noeffective return path for ground fault currents.Les Stoch, P.Eng., is president of L. Stoch & Associates, specialistsin quality management/engineering services. He is a member ofPEO, OEL and IAEI, and develops and delivers electrical code andtechnical workshops for Dalhousie University. He also developedthe Master Electrician training program and exam (Ontario) forthe <strong>Electrical</strong> Contractor Registration Agency. Visit him online atwww.lstoch.com.Sharp-eyed reader alert!A reader spotted an error in my January 2008 column. UnderRule 10-700(3), I incorrectly indicated that a field-assembledground electrode may consist of a copper conductor at least 3metres long. I should have specified 6 metres. Many thanks!Questions and answerscompiled by the <strong>Electrical</strong>Safety AuthorityTackle theCode Conundrum...if you dareSo, you think you know the electrical code, eh? Well, we’ll soonfind out if you’re an electrical code junkie or downright codeclueless.Take a look at the following questions and check youranswers in April’s <strong>Electrical</strong> <strong>Business</strong>.How did you do?3 of 3 – Not only are you smart, you love to show off.1 of 3 – Your understanding of these questions is not up to code.2 of 3 – You’re pretty smart, but you still missed one.0 of 3 – Did you come up with your answers by playing Eenie,Meenie, Minie, Moe?Question 1When applied to x-ray or computerized tomographyequipment, long-time rating means a rating that isapplicable for an operating period of ___ seconds/minutes or more.a) 20 seconds c) 5 minutesb) 1 minute d) 20 minutesQuestion 2Rules for the installation of electrical equipment andwiring in Class I Division I hazardous locations can befound in ___ of the electrical code.a) Section 18 c) Appendix Bb) Section 20 d) Appendix JQuestion 3Where primary windings of current and voltage instrumenttransformers are connected to circuits of 300V ormore to ground, or where the transformers are on switchboardsirrespective of the voltage of the circuits, thesecondary circuits of the transformer shall be grounded.a) True b) FalseAnswers▼▼▼to Code Conundrum<strong>Electrical</strong> <strong>Business</strong> February 2008Q-1: Rigid steel conduit of a minimumnominal size of 53 (2) tradesize shall be permitted to be usedas a consumer’s service mast.b) False. Rule 6-<strong>11</strong>2(5)requires a minimum nominal sizeof 63 (2-1/2) trade size.Q-2: <strong>Electrical</strong> metallic tubing(EMT) is permitted as a wiringmethod in Class III, Div 1 locations.a) True. Rule 18-302.Q-3: A heating cable set is permittedto be installed for freezeprotection in a pipe containingsewage solids.b) False. Rule 62-312(3)says the internal heating of pipes,ducts or vessels should be limitedto those not containing sewagesolids or flammable liquids.ADVERTISER INDEXAdvertiser . . . . . . . . . . . . . . . . . . . . . . . . . . . . .<strong>Page</strong>3M Canada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9Aeroflo, Inc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .<strong>11</strong>Arlington Industries . . . . . . . . . . . . . . . . . . . . . . . .31Arrow Fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . .16Canadian Standards Association . . . . . . . . . 16 & 38Chess Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . .26Fluke Electronics . . . . . . . . . . . . . . . . . . . . . 28 & 36General Electric . . . . . . . . . . . . . . . . . . . . . . . . . . .40Hammond Manufacturing . . . . . . . . . . . . . . . . . . .25Hubbell Canada . . . . . . . . . . . . . . . . . . . . . . . . . . .<strong>22</strong>I.E.D. Limited Partnership . . . . . . . . . . . . . . . . . . .29IPEX Inc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Master Promotions . . . . . . . . . . . . . . . . . . . . . . . . .33Maxis Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19Megger Ltd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25Molex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .<strong>34</strong>Nexans Canada . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Northern Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Osram Sylvania . . . . . . . . . . . . . . . . . . . . . . 13 & 27Power Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Pre-Apprenticeship Training . . . . . . . . . . . . . . . . . .32Schneider Electric . . . . . . . . . . . . . . . . . . . . . 8 & 30Scotiabank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23Standard Products . . . . . . . . . . . . . . . . . . . . . . . . . .2Techspan Industries . . . . . . . . . . . . . . . . . . . . . . . .39Thomas & Betts . . . . . . . . . . . . . . . . . . . . . 1, 5 & <strong>11</strong>Ultrasave Lighting . . . . . . . . . . . . . . . . . . . . . . . . .24Underground Devices . . . . . . . . . . . . . . . . . . . . . . .35United Wire & Cable . . . . . . . . . . . . . . . . . . . . . . . . .4Venture Lighting . . . . . . . . . . . . . . . . . . . . . . 15 & 35VJ Pamensky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6CSA_code_EB_Feb08.indd 138 • MARCH 2008 • www. mag.com2/25/08 9:46:44 AM
IEC309 PIN & SLEEVE CONNECTORSSAFETY PERFORMANCE DURABILITY3,4 & 5 wire connections4 amperage ratings-25°C TO 90°C OP. temp. rating• Watertight - IP67 (indoor/outdoor) 20-100amp• Rugged construction• Quick and easy installation• Single & 3 phase voltage ratings - 6 colourscodes determines size• Splashproof - IP44 (indoor) 20&30ampwww.techspan.biz/pinTECHSPAN SWITCHES & TOGGLESBroadest line of switchesin the industryCSA, UL approvedBlister packed for Counter Display(bulk pack available).AC and or DC ratedMetal or Non-Metallic Actuator MaterialAsk forour 44 pageCatalogueToday!• Medium duty • Std. Pushbuttons• Miniature• Snap Action Switches• Snap Action Switches • Marine Rockers• Medium duty Nylon • Appliance Rockers• Pushbutton• Round Rockerswww.techspan.biz/switcheswww.techspan.bizEmail: sales@techspan.on.ca 1-800-363-1588
Change language