When are two ground rods required for a residential service?

Two ground rods are required for a residential service when the ground resistance exceeds 25 ohms. This requirement is crucial because proper grounding ensures both safety and the effectiveness of the electrical system. A grounding electrode system with a resistance of 25 ohms or less is necessary to ensure that the grounding system can safely dissipate electrical faults to the ground, which minimizes the risk of electrical shock and protects the equipment connected to the electrical service.

Ground rods act as a sink for electrical faults, and if the resistance is higher than permitted, it may not effectively clear fault currents, thus increasing the risk of dangerous conditions. The National Electrical Code (NEC) outlines these standards to help guide the installation of grounding systems, emphasizing the importance of ensuring low resistance values.

While newly constructed houses typically follow certain grounding practices, simply being new does not determine the need for additional grounding rods. The same applies to the service size and the presence of pools on the property—though they can involve unique electrical considerations, they do not directly dictate the requirement for multiple ground electrodes based solely on resistance measurements.