This “earth ground” is a very important part of your electrical system to ensure electrical safety. According to the National Electrical Code, or NEC, a ground system should have a grounding resistance of 25 ohms or less. Achieving this may require more than one ground rod. Ground rods come in both 8-foot and 10-foot lengths, with 8-foot being the most common size used in residential installations. As a rule, ground rods must be a minimum of eight feet long and should not be cut down. In very dry ground, which provides more resistance than moist soil (meaning it does not accept electricity as readily), ground rods are sometimes stacked and joined with a special clamp so they can extend deeper into the earth. Another option is to add a second ground rod. This is usually a better option, but the rods must be at least six feet apart, according to the NEC. Note: Most local jurisdictions and local power companies require the 2-ground rod method to pass inspection. Some counties also allow or require a footing or foundation ground connection for new construction. Whenever possible, ground rods should go into moist soil around your home. Usually, the area close to the foundation has enough moisture due to runoff water from downspouts. It is unwise and unsafe to install the shorter, 4-foot ground rods often sold for grounding things like TV antennas and other individual devices. These are not legal for grounding the home electrical service, and they can cause your grounding system to fail when it is needed most. For 200 Amp services, a #4 grounding electrode conductor (ground wire) is required.
An acorn clamp is an oval-shaped clamp with a bolt used to tighten it to the ground rod. An acorn clamp is the most commonly used clamp for ground rod connections and is approved for direct burial applications. The grounding conductor should be attached to the ground rod and in the “V” of the acorn clamp, opposite the bolt side of the clamp. The brass-toothed clamp is a two-piece clamp that has two setscrews used to secure it to the ground rod. It also has a center point with a hole to mount the wire and a set screw to tighten the wire. This type of clamp is best used inside to make grounding connections around water pipes that are grounded to the ground bus of a service panel.
