Grounding and Power Quality | Fluke

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This illustration shows current paths for grounding stakes from distribution panels to pylons and power poles.
 

The connection between grounding and power quality

Countless facilities support clusters of electronic devices, especially computers and other networked machines. Installing proper grounding and the performance of regular grounding tests can result in consistent power quality.

Grounding is a low-resistance conductive connection between electrical circuits, equipment and the earth. It impacts the stability of reference voltage in a power system. Proper wiring and grounding are required in any electrical system for safe equipment operation. It is essential for a grounding system to last the projected lifespan of the electrical system it supports, even after sustaining large current faults.

Selective earth and stakeless ground resistance tests must be completed during initial installation to verify that minimum resistance requirements are being met. It is mandatory to complete grounding tests after:

In tandem with a grounding test, a soil resistivity test is needed to determine the optimal spot for installation, in compliance with code and industry standards. Ideally, ground resistance should be zero ohms. The National Fire Protection Association (NFPA) and Institute of Electrical and Electronics Engineers (IEEE) recommend a ground resistance value of 5.0 ohms or less. Many military and critical communications sites stipulate significantly below 1 Ohm.

Grounding’s impact on power quality

Aside from preventing catastrophic events such as fires and major injury, proper grounding curbs power quality issues that cause systems, circuits and equipment to operate improperly.

The National Electrical Code® (NEC®) does not allow neutral-to-ground connections that create ground loops because it can cause electrical shock and power quality problems. A ground loop is an electrical circuit that has more than one grounding point connected to earth ground, with a voltage potential difference between the grounding points high enough to produce a circulating current in the grounding system.

A proper ground reference is required for establishing a separately derived system (SDS), an electrical system that supplies electrical power derived or taken from generators, photovoltaic systems, storage batteries, transformers or wind turbines. Most SDSs are produced by the secondary side of a power distribution transformer.

In theory, there shouldn’t be leakage current in equipment or branch circuits. Some leakage current to ground will be present through the building ground system. Leakage current exists because the utility power source is ground at the transformer and the building grounding system is grounded at the service entrance. High current can cause issues, and high ground leakage is typically caused by poor, loose, or damaged neutral connections that increase the total resistance of the neutral conductor.

Installing a proper grounding system not only can save lives and mitigate risk, but it also stops the spread of incongruous currents through communication lines and electrical connections.

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