To understand its importance to a home wiring system, it is important to know something about the nature of electrical energy flow.

The grounding and bonding requirements in this column apply to solidly grounded systems that operate at not more than 600V, such as 120/240V, 120/208V, and 277/480V. 90. %%EOF Obviously, if the ground circuit opens up when a fault occurs, then it is not able to perform its intended function.

The benefits for the building owner are many — maximized equipment protection, elimination of shock hazard potential, increased process uptime, and reduced costs through avoiding expensive machine servicing. In essence, the grounding system is a \"backup\" pathway that provides an alternate route for electrical current to follow back to \"ground\" in the case of a problem in the wiring system.

This is an example of grounding.

Search Products And Discover New Innovations In Your Industry!! During thunderstorms or ground faults, however, an isolated ground rod becomes a liability, creating shock hazard potential for employees and high potential rises on sensitive machine components. <<9D1918B5A5F9CB4E85A09FC06094FA44>]>>

Grounding conductors are sized initially according to NEC Table 250-122, based on the overcurrent protection rating of the circuit. Connect the ground rod to the bonded system and install a grounding conductor from the power source to the sensitive load to eliminate the safety hazard and allow an effective ground-fault return path. The IEEE defines “touch voltage” as “the potential (voltage) difference between a bonded metallic structure and a point on the earth 3 feet from the structure.”, ANSI/IEEE Standard 142, [4.1.1], says the resistance of the soil outward from a ground rod is equal to the sum of the series resistances of the earth shells.

0000041042 00000 n 6 conductor is clamped onto the driven rod. Because the resistance of the earth is so high, very little current will return to the power-supply winding if the earth is the only ground-fault return path.

Some boxes are now available with approved reducing knockouts that do not require jumpers, and are marked to identify them as such. 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. The error is compounded because such isolation does not establish a low-impedance ground-fault return path to the power source, which is necessary to actuate the overcurrent protection device.”.

0000005717 00000 n Circulating currents on equipment grounding conductors, metal raceways, and building steel develop potential differences between ground and the neutral of electronic equipment. Since there is ac current, the term impedance rather than resistance is used, which becomes especially important for long lengths of wiring or higher capacity systems, where the inductive effects can be significant. – The potential difference across insulation materials is limited. • Bonding is the process of connecting to conductive objects together. Search Products And Discover New Innovations In Your Industry. Understanding the difference between bonding/grounding and earthing requires implicit understanding of several important concepts and terms, including those outlined below. Some even imply the machine warranty will not be honored if the ground rod is not installed. However, troubles can arise when terms like “bonding,” “grounding,” and “earthing” are interchanged or confused in certain situations. 2 .Fig. 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.

All rights reserved. The loop impedance is the sum of all impedances in the faulted circuit, including the supply transformer, the ungrounded conductors, and the grounding circuit. Grounded and equipment grounding conductors should never be interchanged. Too often, metal parts are grounded (earthed) instead of bonded.

A conductor used to connect equipment to a grounding (earthing) electrode. The NEC does allow use of metallic conduit and other substitutes, but some industry experts believe these systems are less effective and should be avoided.

An electrically conductive path from a ground fault to the source winding.

Knowing when to ground a generator is critical for operator safety. Instead, a low-resistance ohmmeter should be used, which can measure less than 1 milliohm (1/1000 of an ohm), and can accurately indicate the resistance of wires, connections, and other components in the ground path.

If this bonded system rises in voltage with respect to earth, all machines onboard experience the increase together. Other more complex arrangements are sometimes required.

The maximum fault current that flows is determined from the open circuit voltage and the total loop impedance (Fig. 0000018579 00000 n With the proliferation of sensitive electronic and computerized equipment, as well as harmonic producers such as solid state drives, the issue of electrical “noise” has become of much greater importance.

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For example, many industrial equipment manuals require violating 250.24(A)(5) as a condition of warranty.

In particular, they require installing an “isolated grounding electrode.” By this, they mean an electrode without a low-impedance fault-current path back to the source winding (other than through the earth itself). – Nonmetallic conduit, fittings, or boxes would interrupt a grounding circuit through the conduit. Where the NEC uses the term “grounding” to mean “connecting to the earth,” “earthing” will follow in parentheses. • Grounding electrode (earthing). This grounding electrode could be an underground water pipe, structural member, or fabricated ground rod; and in many cases consists of more than one of these bonded together. All these years in the field we’ve been using a floating system. What is grounding exactly?



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