Ground Faults in Photovoltaic Systems

Jeffrey R. Jowett, Megger Columns, Spring 2022 Columns, Tech Tips

Solar farms, which are exposed to the elements, are especially at risk for failure and require dedicated electrical maintenance. Good grounding is essential, as the panels produce high DC voltages that can be sources of shock and fire, as well as induced voltages and electromagnetic interference on lines. With respect to grounding, there are two types of photovoltaic (PV) systems: …

Grounding and Bonding Meter Sockets

Jeffrey R. Jowett, Megger Columns, Tech Tips, Winter 2021 Columns

In an actual reported case, a severe storm blew down a large tree that struck a residence. A meter that should have been reporting 240 V reported a phase-phase voltage of 124 V. The falling tree had pulled down the service, which had then been re-attached by a service crew. A routine voltmeter check revealed 118 V between the left hot leg and neutral, …

The Importance of Grounding Renewables

Jeffrey R. Jowett, Megger Columns, Fall 2021 Columns, Tech Tips

The rapidly developing industry of renewable power generation can be compared to an hourglass. Inexhaustible supplies of free resources — sun and wind — are converted into a corresponding outflow of electrical energy at notable return on investment. But the process includes the neck of the hourglass through which the resources must pass. This is the solar array or wind …

Earth Resistivity Test Methods and Evaluations

Jeffrey R. Jowett, Megger Columns, Summer 2021 Columns, Tech Tips

Ground testing is often thought of as ground electrode testing: the measurement of the resistance associated with a particular rod or grounding system. A useful corollary to this is soil resistivity testing. Resistivity is the electrical property of soil itself that determines how well it can carry current. It varies enormously (Table 1) depending on physical and chemical composition, moisture, …

Application of Crushed Rock in Substations

Jeffrey R. Jowett, Megger Columns, Spring 2021 Columns, Tech Tips

Although it can readily be overlooked, an important and fundamental consideration in any electrical application is safety, and one of the most effective tools in the application of safety is redundancy. If one safeguard fails, there’s another right there to act as a safety net. There’s hardly a greater necessity for redundant safety than in a substation, where arcing could …

Ground Testing Procedures

Jeffrey R. Jowett, Megger Columns, Tech Tips, Winter 2020 Columns

Effective ground testing is an informed combination of instrumentation and procedure. Accuracy, resolution, safety, noise suppression, graphics, clamp features, and general reliability are all critical, as they are with any electrical testing. But effective and accurate ground testing depends as much on adherence to procedure as it does on quality of instrumentation. If the operator does not understand and diligently …

Medium-Voltage Grounding

Jeffrey R. Jowett, Megger Columns, Fall 2020 Columns, Tech Tips

First, let’s look at some industry-accepted definitions to establish context. Low voltage is anything below 1 kV. The common building-wiring voltages are 120, 240, 480, and 600 V. To the uninitiated, this can seem confusing and even ridiculous. Get across 600 V, and it can fry you like bacon, but in industry parlance, it is still low voltage. Put into …

Tracing Ground Leakage with a Clamp-Meter

Jeffrey R. Jowett, Megger Columns, Summer 2020 Columns, Tech Tips

The clamp-on current meter that appeared in the late 20th century was a blessing to everyone working in electrical testing. It improved the vital measurement of one of the three components of Ohm’s Law by a quantum leap. No more difficult, costly, time-consuming, and potentially dangerous direct connections to live circuitry. Just clamp a pair of jaws around a conductor …

Monitoring a Grounded System

Jeffrey R. Jowett, Megger Columns, Spring 2020 Columns, Tech Tips

Electrical faults cause enormous damage due to fires and loss of equipment. But of far greater importance is the danger to human life through electrocution. Ground faults in particular pose the risk of death because a human is generally at ground potential, thereby providing an alternate current path. It takes only about 5 mA to cause a shock, and as …

Another Test for Lightning Protection

Jeffrey R. Jowett, Megger Columns, Fall 2019 Columns, Tech Tips

It doesn’t take an electrician or engineer to know that lightning is a major cause of electrical interference and damage. Protecting the electrical system against such a danger is paramount. A lightning stroke can be hotter than the surface of the sun, with voltage estimated as high as 120 million volts, including 400 kA and 500 megajoules of energy. Utility …