Equipment grounding (bonding) conductor. The low-impedance fault-current path used to connect the noncurrent-carrying metal parts of equipment, raceways, and other enclosures to the grounded (neutral) conductor and equipment grounding (bonding) conductor at service equipment or at the source of a separately derived system. While this practice may reduce data errors in sensitive process machines, it violates the NEC, creates a shock hazard for employees, and causes a potential difference that may damage sensitive electronic components. Kirchoff's current/voltage laws, superposition and thevinens. What is grounding exactly? Proper grounding and bonding result in a system that is safe and reliable. The voltage at the location of a ground fault with respect to the earth can be determined from the fault current and the ground circuit impedance (Fig.

Note that earthing is not required for sensitive machine operation. – Nonmetallic conduit, fittings, or boxes would interrupt a grounding circuit through the conduit. There is a bare, solid copper No. To learn more about grounding and bonding, sign up for a JADE Learning electrical continuing education course. Check back in the next week or so. More importantly, you'll encounter them in your work — where a solid understanding of grounding- and bonding-related terms will allow you to avoid mistakes, such as those in the street lighting example. Knowing when to ground a generator is critical for operator safety. After finding out that we are completely out of EMT (metal thin-wall) conduit on the jobsite, I decide to install a 10’ piece of PVC (plastic) conduit between the three metal boxes so that I can complete the job today. 0 Other standards agree: ANSI/IEEE Standard 142, Recommended Practice for Grounding of Industrial and Commercial Power Systems (Green Book) and Soares Book on Grounding use the same physics and electrical theory as Art. The same problem occurs if a high-impedance voltmeter is used between a line and ground. What is bonding? 0000004844 00000 n The Table lists the percentage of total resistance and the touch voltage for the light pole in Fig. The earth is a poor conductor. All wire terminations must be an approved mechanical type or welded. Copper wires should be used for grounding whenever possible. In addition, non-current-carrying metallic components in a facility, such as equipment cabinets, enclosures, and structural steel, need to be electrically interconnected so voltage potential cannot exist between them. The NEC uses the phrase “ground-fault current path,” but fault current isn't traveling to the earth — it's traveling to the source winding of the power supply. – Whenever there is uncertainty about the existence of a reliable electrical connection, a bonding jumper should be used. For example, with a fault current of 100 amp, a 0.1-ohm ground impedance would produce 10 V at the fault location. In the beginning pages of the standard, its purpose is clearly stated as “the practical safeguarding of persons and property from hazards arising from the use of electricity.” To take it a step further, the purpose of the NEC could never be accomplished without the proper application of Art. Knowing that the NEC Code-Making-Panel was considering replacing this term with the word “earthing” gives us a good indication of just what the term is trying to relay to us: to wit, “grounding” means to provide a conductive path between electrical equipment and the earth. How to ground an antenna for RF performance: Some types of antenna are unbalanced and are designed to operate with a ground connection to enable them to operate correctly. 0000006015 00000 n 3). Coming posts will address this in more detail! For systems without a neutral, the ground location could be any point. The grounding pathway is generally formed by a system of bare copper wires that connect to every device and every metal electrical box in your home. Securing is done by installing a mechanical means of at... Air-Conditioning and Refrigeration Systems, There are quite a few challenges to hurdle over when installing or upgrading HVAC systems for historic buildings. If the people involved in street lighting and traffic signaling in these locations where the Code is misapplied understood the terminology of Art. The grounded circuits of machines need to have an effective return path from the machines to the power source in order to function properly. An electrical panel is installed outside of a dwelling unit and there is a copper ground rod driven into the earth below. Illustrated Catastrophes: 400.7, 400.8, 400.8(1), Art. 0000001558 00000 n If multiple paths exist, the current splits, with the most current flowing through the lowest impedance. An unintentional connection between an ungrounded conductor and earth or metallic parts of enclosures, raceways, or equipment (Fig. Power sources fall into four general categories: Transformers, generators, electric utilities, and static power converters. Balanced antennas like dipoles do not need an RF ground for their correct operation as long as common-mode currents are kept off the feeder. The maximum fault current that flows is determined from the open circuit voltage and the total loop impedance (Fig.

All rights reserved. The most common grounding electrode for small facilities is a metallic ground rod, but earthing systems for larger buildings can — and should — be more elaborate and include the means by which to inspect and test these systems periodically. Modern clothes dryers often have a bonding strap in place that connects the metal housing of the dryer to the neutral lug of the cord attachment termi... A “COMBINATION” Arc-Fault Circuit Breaker is NOT equivalent to a “DUAL-FUNCTION” Circuit Breaker.

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