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. But 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 the 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. The first is:

1. Improper replacement of non-grounding receptacles. Dwellings and non-dwellings often contain non-grounding receptacles. It’s 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.

There are several ways you can complete this upgrade, many of which are erroneous and strictly against the Code. For example, never apply the following non-NEC-compliant solutions:

• Hook up a new grounding receptacle on the theory that this is a step in the right direction. This can lead future electricians and occupants to believe they are fully protected by a non-functioning ground receptacle.
• Connect the green grounding terminal of a grounded receptacle via a short jumper to the grounded neutral conductor. This practice is totally non-compliant and dangerous because when a load is connected, the voltage will appear on both the neutral and ground wires. Therefore, any non-current-carrying appliance or tool case will become energized, causing shock to the user, who is typically partially or totally grounded.
• Run an individual ground conductor from the green grounding terminal of a grounded receptacle to the nearest water pipe or other grounded object. This “floating ground” presents various hazards. It is likely that this ground rod of convenience will have several ohms of ground resistance so that, in case of the ground fault within a connected tool or appliance, the breaker will not trip — and exposed metal will remain energized.
• Run an individual ground conductor back to the entrance panel and connect it to the neutral bar or grounding strip. This solution is somewhat better but still noncompliant. Any grounding conductor must be within the circuit cable or raceway. One objection is that an individual conductor could be damaged or removed in the course of work taking place in the future.

To read the correct ways to handle this type of situation, when you find yourself working with non-grounded receptacles, and to review the remaining nine examples, click here