There are two types of ground testing that should be performed at your facility. The first is done during the building process to ensure that the electrical system is installed properly. The second is routine ground testing that should be completed to make certain the grounding system continues to function in the manner it was designed. This ground testing must be done correctly, as errors can be dangerous and costly.
The grounding path provides a low-resistance path for electricity to travel. Electrical power must travel from the source through a load and then return to the source through the neutral connection. The ground connection offers a secondary path for safety. This return path must provide the least resistance to the current. The general requirement of the National Electric Code (NEC) is no more than 25 ohms of resistance.
Bonding offers a connection to all of the ground conductors of an electrical system. Grounding fault systems primarily protect equipment, while ground fault circuit protection keeps individuals safe. However, the best grounding system in the world will not provide any protection if the electrical components in your facility are not bonded to it. Likewise, bonds will not offer protection without grounding.
Not having a solidly grounded system can result in the loss of expensive equipment, critical data and even human lives. Equipment without adequate grounding can experience damaging spikes or voltage surges. The loss of ground can cause sensitive equipment to lose data or process it incorrectly.
Intermittent failures can also create problems from random electrical shocks to equipment failures that are difficult to locate. The equipment often is blamed for the failure when, in fact, it is a lack of a solid ground. For example, when random electrical shocks were experienced in a fire station shower area, it was determined after extensive testing that a portion of the building was operating like a capacitor. Static electricity was building up, and without a proper ground bond, the electricity discharged through an individual using the facilities. The problem was intermittent because it took time for enough energy to build up and reach a discharge potential.
Over time, connections or bonds can loosen. The wrong materials used to form the initial connection can fail even after being previously adequate. Corrosion can damage the connectors and the ground rods. In one extreme case, chemicals were contained in soil-dissolved ground rods that had been fully tested at installation. While the tops of the grounding rods were present and visible, only a few inches of material were remaining.
The correct methods and equipment must be used to produce the right data for your grounding system. For example, a clamp-on test or stakeless method enables testing to be faster and easier. However, it should not be used to measure soil resistance. This technique is also not recommended for complex grounding systems that have a metallic loop.
All factors of the grounding system must be calculated properly. For instance, after heavy rainfall, the soil being tested might offer much less resistance than it would under normal conditions.
Thorough ground testing should be part of your facility’s complete electrical maintenance plan. The 2015 edition of the National Fire Protection Association’s 70E standard includes new requirements for electrical safety. Make sure your facility is in compliance.
Bob Sheppard is the founder, president and general manager of Southwest Energy Systems, an International Electrical Testing Association accredited testing and engineering firm.