Grounding & Bonding is oftentimes overlooked, but is an extremely important aspect of proper building design, as most power quality and safety issues arise from misapplication of grounding requirements. A proper grounding system design will ensure equipment protection, personnel safety, lightning dissipation, electrostatic discharge (ESD), and reduce signal noise in electronic equipment. In 1893, the first nationwide code was adopted for acceptable electrical system installation practices in buildings. These rules are now a publication of the National Fire Protection Association (NFPA) and are revised and amended on a 3-year cycle.
This document has an entire article devoted to the subject of grounding and its requirements. Despite these regulations, a large portion of building fires are a result of electrical system events that could have been mitigated by proper application of these requirements. It's important to note that the National Electric Code (NEC) is primarily concerned with protection of life and property and generally do not ensure efficient system operation or provide for electromagnetic compatibility (EMC). For example, a telecommunication installation could experience malfunctions and failures from deficiencies in the power and grounding systems even though the installation of both are code compliant. With the increase in newer, more sensitive, highly integrated electronic equipment, designing a proper grounding and bonding system beyond code the minimums has become a top priority.
There is often confusion between the use of the words "grounding" and "bonding." To make matters worse, they usually are not expressly clear in the various codes. In simplest terms, grounding is the actual connection to earth and bonding is the connection of two bodies together to form a continuous electrical path. The confusion often happens because the bonding of metallic bodies usually provides an electrically conductive path to ground. Examples of bonding and grounding are illustrated in the figures below:
Grounding & Bonding involves several unique but interrelated systems, all of which contribute to the safe operation of the power system and the equipment supplied by it. Among these systems are:
- System Grounding
- Equipment Grounding (Bonding)
- Grounding Electrodes
- Telecommunications Bonding Infrastructure
- Lightning Protection System
I’d like to turn our focus to the grounding electrode system, as it's the most critical to the overall performance of the systems listed above and often one of the hardest to design. Grounding electrodes can be classified into two general categories – Natural Electrodes and Made Electrodes.
Natural Electrodes are items such as underground metallic piping, concrete encased rebar, and building steel. These often exhibit some of the lowest resistances, but can be damaged or altered during building renovations. Therefore natural electrodes should be supplemented with Made Electrodes; which can take the form of copper rings, rods, and plates.
Depending on soil conditions, designing a grounding electrode system with low system resistance can be very expensive. For example, with average-to-high soil resistivity, a code minimum 25 ohm system would only require 3 copper ground rods whereas over 100 copper ground rods would be required to achieve a 1 ohm impedance.
While many telecommunications design guides recommend a system impedance as low as 0.1 Ohms, site conditions could make the required design cost prohibitive. The owner and designer should determine the electrode design and system impedance based on facility size and use, environmental risks, available power system fault current, and the cost of downtime for any critical electrical systems located in the facility.
Finally, in order to properly maintain the grounding electrode system performance over the lifespan of the building, it is important to implement an effective maintenance schedule and administration system. To allow for proper maintenance, at least one ground test well should be provided in the design to allow for routine resistance checks by building staff.
Additionally, all grounding and bonding conductors and busbars should be properly labeled and documented in records to avoid any inadvertent disconnections and allow for quick troubleshooting and repair activities.