Ground Bars are Vital Safety Equipment
Ground bars are vital safety equipment and often misunderstood. They are much more than bars of copper with holes. Grounding systems are used, not just because there are rules requiring them, but because they have a very important function. They keep us safe and make things work like they should. Few people truly understand why ground bars are used or how they work.
They provide a common reference potential (equipotential plane) between the electrical service and the connected equipment. This protects people and equipment. The way this happens may require some explanation. Line to ground faults represent approximately 98% of electrical faults. Equipment is (or should be) connected so that the exposed components and grounded parts are at a common potential. When a live conductor comes in contact with a grounded metal case or container the live conductor is pulled down to ground potential. This is known as a short to ground. In a properly grounded system a short to ground causes a circuit breaker to trip, a fuse to blow or a ground fault detector to open the circuit. This is the safety of the system. The size of a conductor used to make connection to a ground must be sized large enough to carry enough current to active the protective device of the circuit. It must be able to blow a fuse or trip a breaker. Ground-fault detectors will trip at a much lower current.
If a piece of equipment is not properly grounded it can become energized with the same potential as the live conductor. If a person comes in contact with a piece of ungrounded equipment that is energized the result is electrical shock often injury or death. The protective devices such as fuses and circuit breakers will not detect a shorted conductor to frame and will not de-energize the system leaving a piece of equipment dangerously energized.
Standard Types of Ground Bars
In the 1940′s and 1950′s intentionally ungrounded systems were used. In some older equipment these two-wire systems are still found. When used near grounded equipment there exists a potential for electric shock. A short to frame will make the frame equal in potential to the shorted circuit. A person coming in contact with this piece of equipment and a grounded piece of equipment might experience a shock. These systems use a ground detector arrangement of lights to indicate when a fault to ground exists. A short to ground in one of these systems is very difficult to locate and correct.
There are companies that specialize in manufacturing ground bars. They offer several standard types and styles or can manufacture custom grounding systems if required. These companies are also good sources of information about equipment grounding requirements.
There are NEC, UL and CSA standards for grounding systems. Anyone designing a new installation or revisions to existing equipment should become familiar with the relevant standards or call in an expert for advice. Being sure of the grounding system will make everyone in the organization safer for a long time.
