Today's market for grounding work is vast and largely untapped. While industrial customers are usually aware of the need for good grounding, commercial and residential customers usually are not. Your target market with residential grounding is the owner of the higher-value home. The typical new home is "intelligent," with electronics embedded everywhere. High-end new homes have automated systems (zone temperature, security and lighting); communication (security and fire alarm, intercoms and networks); entertainment (high-end stereos, televisions, VCRs and DVDs); high-end appliances (refrigerators that cost five figures); computers (workstation-grade); and other expensive necessities.
Owners of these homes don't want to hassle with maintenance or repairs. Some lease a service entrance surge protector to protect their homes; others rely on point-of-use surge strips. The more technically savvy assume the $1,600 they spent on distributed UPS systems-which they probably networked-will protect their expensive electronics from damage. What many of these people don't know is their transient protection can't do its job without a good grounding system-and bonding is part of the equation. That's where you come in.
Many utility installers (electric, cable TV or telephone companies) drive a dedicated ground rod. Their intent is to provide a low impedance grounding system for their equipment. Unfortunately, they usually fail to bond the ground rods together to form a system. That can mean more insurance claims for homeowners due to damaged electronics. TVs, computers, stereos and alarm systems all connect to more than one system. If the ground potential is not the same on all systems, it's only a matter of time before major damage or personal injury occurs. To fix this, bond all driven ground rods together to form a grounding system. A solid No. 4 bare wire is usually a good bonding jumper for home grounding situations. However, you should always refer to Secs. 250-28(d) and 250-102 of the National Electrical Code (NEC) to determine the minimum size you need. In most cases, it's good practice to exceed that minimum by two or more wire sizes.
To satisfy NEC requirements, you drive two ground rods, bond the service at the rods and at the water service entrance, and call it a day. However, such a scheme is inadequate for today's home. The NEC's requirements for residential grounding are strictly for the safety of the inhabitants-not the equipment. With the proliferation of electronic devices in the home, grounding is no longer just a safety issue. Old and new homes typically have horrendous grounding systems. To compound the problem, the homeowner makes amateur modifications and doesn't perform maintenance. You can offer the homeowner a grounding survey and a cure to problems that could zap high-dollar possessions.
Let's look at a case study. Although this scenario describes a residential project, the same lessons apply to commercial and industrial grounding systems.
We selected a 10-year-old single-family dwelling for our grounding project. Our initial survey showed the electrical service (grounding electrode conductor or GEC) bonded to the water service entrance and a supplemental ground to a driven rod, per NEC requirements. At first, it seemed the homeowner had nothing to gain from work on this system. That wasn't the case.
We used a clamp-on ground resistance meter (Photo 1) to measure the ground resistance before making any modifications to the grounding system. We compared this meter to another manufacturer's four-point ground tester (Photo 2) and found it to be accurate. The clamp-on ground resistance meter allows you to accurately test your ground impedance and your bond to ground, thus giving you the overall ground resistance without shutting off power to the building. No wonder these devices are so popular with data centers and other 24/7 operations.
Our visual inspection revealed several deficiencies. First, the cable company installed a dedicated ground rod about 4 ft from the electrical ground rod. Earth was the only electrical bond between these rods. To top it off, the grounding conductor between the cable entrance and its ground rod was broken (Photo 3).
Then, we found the bonding conductor between the gas pipe and service ground rod not connected. Next, we noticed the phone company did bond to the electrical ground rod. However, it used the same bonding clamp as the electrical service. (Using two wires in one clamp obviously reduces clamping tension and increases resistance. Unless you use a clamp listed for such service, you violate Sec. 250-70). Finally, corrosion existed at all of the connections.
We spent less than $15 on supplies to remedy these problems. The supplies were 20 ft of No. 4 AWG solid copper wire, ground rod clamps, a pipe bonding clamp and emery cloth. First, we bonded the cable TV rod to the phone rod, and the phone rod to the service entrance rod. Then, we bonded the natural gas pipe to the service entrance rod, and repaired the connection from the cable TV entrance to the cable TV ground rod. What about trenching? We used a sidewalk ice scraper to wedge a small trench next to the foundation. This had no effect on the lawn, and it took only a few minutes.
We went after the existing bonds next. We broke, cleaned and remade them-one at a time (Photo 4). Remember: Always leave at least one grounding electrode conductor made at all times-unless you disconnect the electrical service (i.e. power down the building). We took ground resistance readings again, with the clamp-on ground resistance meter (Photo 5). The before-and-after measurements (See table on page 24D) showed significant improvements in the ground resistance after the repairs.
Grounding work can be very profitable, but there's a catch: Home configurations vary. To quote a fair price, you must first conduct a site survey. A clamp-on ground resistance meter (though not required) is handy for this task. However, make sure you understand the operating instructions for this type of meter. Measuring the ground resistance at the wrong location will determine the resistance of a ground loop. If the ground resistance is less than one ohm, you are probably (but not necessarily) measuring the resistance of a loop. It's also good practice to calibrate the tester before each job. Use your four-point soil resistance tester to see if existing rods are still functional, but remember to disconnect and test them one at a time.
In a typical residence, a GEC bonds the service disconnect/panelboard ground bar to the water service entrance. A supplemental ground bonds the service to a driven rod. If possible, inspect these conductors over their entire length to locate breaks or other damage. Conductors must terminate with a proper bonding clamp. When you find a bond with corrosion, make a note to break it apart, clean and remake it. Determine if you need to shut off the electrical power before breaking the GEC bond. If the water pipe bond is functional, you won't need to. If the GEC to the driven rod is exposed, protect the conductor by routing it in nonmetallic conduit. Neutral-ground bonds on the load side violate section 250-24(a)(5) and create circuit-protection problems. Many homeowners apply the "if one is good, then two must be better" philosophy to subpanels. If the panel comes with such a bond, remove it. The typical homeowner doesn't know to do this.
What about homes without equipment ground conductors? One option is to rewire the home completely. A less expensive option is to install dedicated circuits with an EGC to support any susceptible electronic equipment. You can often accomplish this at low cost by using surface-mounted wireways. Many of these systems are quite attractive, and they allow for future modification. While you're at it, be sure to install GFCI receptacles in bathrooms, the kitchen, garage, basement and outdoors. A GFCI doesn't require an EGC for proper operation, but you do need one for surge protection. Keep the two concepts separate.
Transient Voltage Surge Suppression (TVSS) devices are also available at a reasonable price for residential services. What's the selling point for these devices? They protect your PC, VCR, DVD or home theater system. You can install them at the service entrance as a first line of defense for the entire electrical system.
Secondary surge suppressors or point-of-use devices guard against additional problems. Don't forget to install surge suppression on the telephone lines and cable TV-and DSL or ISDN equipment if it's there. You can go one step further by recommending point-of-use UPSs with communication line protection. With a good grounding system in place, these devices provide a high degree of protection.