Taking the Low Ground
No matter what your level of technical expertise, one area that can cause confusion is the proper bonding and grounding of electrical systems such as security, audio-visual, CCTV and access control.
Today, electronic systems consist of many components and are often installed in a racking configuration. Even residential systems, with today’s computer, security and entertainment networks, are large enough to have racks for primary components, and remotely located subsystem equipment racks as well. Multiple systems with different technologies may also be working from the same power source in these facilities.
Since these systems are typically in large, heavy metal racks or cabinets, one can assume all must be well with electrical safety and operational performance. Nothing could be further from the truth. More may be needed than just bolting equipment into a rack and plugging power into the wall.
One popular expression comes to mind when we talk about the bonding and grounding of electrical systems. Many of us have heard the expression, “Knowing just enough to be dangerous.” Understanding and navigating one’s way through the maze of rules, standards, and practices of bonding and grounding systems can be both confusing and challenging for even veteran technicians.
This month, we will take a look at some best practices and even some myths when it comes to grounding and bonding.
Basics of Grounding and Bonding
First, let’s look at a definition of bonding and grounding.
Grounding refers noncurrent-carrying, accessible parts of electrical circuits to ground (earth) as protection from hazards such as electrical voltages, static charges, voltage spikes or inadequate insulation. Bonding refers various ground circuits to a common grounding electrode system to avoid voltage potentials between them.
Seems simple and straightforward enough, so what is the big fuss? Let’s move forward.
Presently, National Electrical Code (NEC) 2008 (Article 250; Standard 467 in UL) is the technical bible used by inspectors and authorities having jurisdiction (AHJs) for enforcing electrical bonding and grounding practices. On the other hand, equipment manufacturers may insist on installation modifications using ground isolation devices in order to perfect the performance of the equipment.
This is the fine balancing act that the technician has to perform — making sure the system is electrically safe and following NEC, while also optimizing performance according to the manufacturer’s guidelines. I am not inferring manufacturers are not concerned about safety; however, they often must be creative with these configurations to keep the outside influences of noise and voltage transients from upsetting equipment performance. Now, do you get the picture?
Digging Deeper Into Grounding
One must understand there are a few meanings for the word “ground.” As indicated above, the most common defines an electrical return path for fault current. This can further be interpreted as a return path through the earth or a building and/or system structure.
Another type is known as a “signal ground,” sometimes called a “technical ground.” While the ground connections are similar the challenge is to not allow technical grounds to mix with power grounds past the initial power distribution point.
Some examples would be a technician experiencing noise on a home audio system or CCTV system. When considering ways to eliminate the problem, one method would be to remove the connection from the equipment, but this would create a shock hazard by having no fault return path. I have seen customers get shocked on isolated metal video monitor enclosures.
Another method would be to provide an auxiliary earth ground at the equipment location. Not only can this cause a dangerous fault return path, it can also induce a voltage potential between the original earth ground and the auxiliary ground. This can also result in a “ground loop” effect that can increase rather than reduce signal noise. Remember that an AC-grounded device on the signal ground can also cause a performance issue.
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