Grounding and bonding devices are used in all types of electrical equipment and are an essential component of any electrical system in both commercial and residential applications. Most power quality problems are related to grounding and neutral size issues at an estimated cost of $15 billion to $30 billion annually. A properly installed grounding system employing grounding and bonding equipment helps ensure personnel safety, equipment protection, lightning dissipation, electrostatic discharge (ESD) and the reduction of signal noise in electronic equipment.
Why implement grounding protection?
The grounding system is a basic part of any electrical installation, and aims to:
– Limit the potential difference between metallic masses and ground.
– Make sure the protection devices operate.
– Eliminate or reduce the risk posed by a fault in the electrical equipment used.
Grounding Material Selection
There are three main parts to any grounding system after the protection device: The grounding plane, the grounding wire, and the bond between them.
The grounding plane:
- The best grounding planes are: a.
a. Copper or copper clad ground rods driven into the earth
b. Copper water pipes or other building grounds, such as metal structural frame
c. Metal enclosures and casings (which in turn should be grounded to earth ground)
2. Grounding rods should be either copper or galvanized steel, and have a minimum diameter of 5/8 inch.
3. Aluminum should not be used in direct soil burial as a grounding rod since the alkalinity of the soil will etch the metal. This causes disconnection and an increase in impendence between the grounding system and earth ground.
The grounding wire:
1. Use heavy wire gauges (10 AWG or larger) for running the grounding wire. This is important as a thicker wire gauge, along with a short cable, runs the impendence of the grounding wire lower, keeping voltage drops during surges to a minimum.
2. The cable can be either solid or stranded (just as long as it is a heavy-enough wire gauge). The wire can be either bare or insulated.
The bond between them:
1. The use of dissimilar metals for connection from the surge protection device to the grounding plane should be avoided. Over time the connection can wear down and cause undesirable effects on the grounding system as the connection will degrade due to the oxidized layers that form between them.
2. Ground wires should be bonded to the grounding plane (such as grounding rod or copper water pipes) using grounding clamps. Be sure to pick a clamp that matches the size of either the rod or pipe.
3. Both copper and aluminum are UL-approved for use in grounding protection systems. However, copper is a better conductor of electricity and can be used in smaller gauges.
There are two main types of protection that depend on the ground connection for their proper operation. These are surge protection (transient overvoltage protection for equipment) and earth leakage protection (protection of personal from indirect contact, i.e. electric shock).
The effects of transient overvoltage on an installation are avoided using surge protection devices (SPD). These work by shunting the overvoltage energy to ground, thus avoiding damage to electrical and electronic equipment.
The quality of surge protection is closely linked to the grounding system, since a high impedance path may increase the exposure of sensitive equipment to the effects of the surge. In fact, in the event of complete loss or lack of a ground connection, the surge protection loses all effectiveness.
Proper Installation Guidelines:
1. Do not sharply bend the surge protection wires during termination. Offer a straight path to ground.
2. Keep the surge protection wires as short as possible to improve effectiveness and response time.
3. Keep the surge protection device a few feet away from the protected equipment to allow enough response time for the transient voltage to be suppressed.
4. Ensure all systems connect to the same grounding point only once. Multi paths to a ground plan create different voltage potentials on the system that can result in transient surges. This simply means only pound one copper rod in the earth for grounding.