Proper grounding and bonding prevent unwanted voltage on non-current-carrying metal objects, such as tool and appliance casings, raceways, and enclosures, as well as facilitate the correct operation of overcurrent devices. Beware of wiring everything to a ground rod and considering the job well done. There are certain subtleties you must follow to adhere to applicable NEC rules and provide safe installations to the public and working personnel. Although ground theory is a vast subject, on which whole volumes have been written, David Herres, in his article in EC&M magazine, asks us to take a look at some of the 10 most common grounding errors you may run into on a daily basis.
(10) Failure to bond equipment ground to water pipe.
Improper connections are often seen in the field. Screw clamps and other improvised connections do not provide permanent low impedance bonding. The worst method would be to just wrap the wire around the pipe or to omit this bonding altogether.
(9) Failure to properly reattach metal raceway that is used as an equipment-grounding conductor.
When equipment is relocated, replaced, or removed for repair, many times equipment ground paths are broken. If these connections are not fixed, there’s an accident waiting to happen. Setscrews, locknuts, and threads should be fully engaged and continuity tests performed before equipment is put back into service. Dirt and corrosion can also compromise ground continuity.
(8) Failure to install a second ground rod where required.
A single ground rod that does not have a resistance to ground of 25 ohms or less must be augmented by a second ground rod. Once the second ground rod is installed, it’s not necessary for the two to meet the resistance requirement. As a practical matter, few electricians do the resistance measurement.
(7) Failure to properly attach the ground wire to electrical devices.
Wiring daisy-chained devices in such a way that removing one of them breaks the equipment grounding continuity is a common problem. The preferred way to ground a wiring device is to connect incoming and outgoing equipment-grounding conductors to a short bare or green jumper. The bare or green insulated jumper is then connected to the grounding terminal of the device.
(6) Failure to ground submersible well pumps.
At one time, submersible well pumps were not required to be grounded because they were not considered accessible. However, it was noted that workers would pull the pump, lay it on the ground, and energize it to see if it would spin. If, due to a wiring fault, the case became live, the overcurrent device would not function, causing a shock hazard. The 2008 NEC requires a fourth equipment grounding conductor that you must now lug to the top of the well casing. Many people assume that in a 3-wire submersible pump system one wire is a ground. In actuality, submersible pump cable consists of three wires (plus equipment-grounding conductor) twisted together and unjacketed. Yellow is a common 240V leg, black is run, and red is start, which the control box energizes for a short period of time. Prior to the new grounding requirement, everything was hot.
(5) Improperly grounding frames of electric ranges and clothes dryers.
Prior to the 1996 version of the NEC, it was common practice to use the neutral as an equipment ground. Now, however, all frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of these circuits must be grounded by a fourth wire: the equipment-grounding conductor.
(4) Improperly connecting the equipment-grounding conductor to the system neutral.
You must connect a grounded neutral conductor to normally noncurrent-carrying metal parts of equipment, raceways, and enclosures only through the main bonding jumper (or, in the case of a separately derived system, through a system bonding jumper). Make this connection at the service disconnecting means, not downstream. When you buy a new entrance panel, a screw or other main bonding jumper is usually included in the packaging. Attached to it are instructions stipulating that it is to be installed only when the panel is to be used as service equipment.
(3) Non-installation of GFCIs where required.
Recent Code editions have mandated increased use of GFCIs. In dwelling units, GFCIs are required on all 125V, single-phase, 15A and 20A receptacles in: bathrooms; garages; accessory buildings with a floor at or below grade level not intended as a habitable room, limited to storage, work and similar areas; outdoors; kitchens along countertops; within 6 feet of outside edge of laundry, utility, and wet bar sinks; and boathouses. In other than dwelling units, GFCIs are required on all 125V, single-phase, 15A and 20A receptacles in bathrooms, kitchens, rooftops, outdoors, and within 6 feet of the outside edge of sinks.
(2) Installation of a satellite dish, telephone, CATV, or other low-voltage equipment without proper grounding.
If you look at a number of satellite dish installations in your neighborhood, a certain percentage will inevitably not be grounded at all. Of those that are grounded, there is still a high probability many are not fully compliant. For example, the grounding electrode conductor could be too long, too small, have unlisted clamps at terminations, have excess bends, or be connected to a single ground rod but not be bonded to other system grounds.
(1) Improper replacement of non-grounding receptacles.
Dwellings and non-dwellings often contain non-grounding receptacles. It is perfectly fine to leave the old two prongers in place. But because an intact functioning equipment ground is such an obvious safety feature, most electricians tend to replace these old relics whenever possible.