Monday, 20 May 2019

Avoid Making These Grounding Mistakes

avoiding grounding mistakes

Electrical grounding is a safety measure performed to prevent electrical hazards. It protects you from unwanted voltage on non-current carrying metal objects, and also helps in the operation of overcurrent devices. However, when attempting to safely do the process, there are several grounding mistakes that are committed. Adhering to NEC’s grounding rules can help you avoid these errors. This article will review some of these grounding mistakes to prevent future problems.

Common Grounding Mistakes

electrical grounding mistakesGrounding Mistakes Made While Replacing Non-Grounding Receptacles: Manufacturers are phasing out non-grounded, or two pronged, receptacles. These are replaced by their safer, three pronged counterparts. If they are present in your home, you don’t need to immediately replace them, unless a professional electrician suggests. In case it’s necessary, here are some grounding mistakes that you need to avoid to prevent potential hazards:

  • Replacing a two prong outlet with a three prong without making sure that new receptacle is completely grounded. This can lead occupants and future electricians to believe they are being protected by an outlet that is functioning safely when it is actually putting the occupants at risk for an electrical fire.  Don’t be fooled into thinking that all three prong receptacles are safe! Make sure they are all properly grounded.
  • Connecting the green grounding terminal of a grounded receptacle via a short jumper to the grounded neutral conductor. This will cause a voltage to appear on both the neutral and ground wires once the load is connected. Any non-current carrying appliance or tool that comes into contact will become energized, resulting in shocks.
  • Running an individual ground conductor from the green grounding terminal of a grounded receptacle to the nearest water pipe or other grounded objects. These grounded objects,also considered ‘floating grounds’, will have several ohms of resistance so that if there is a ground fault within a connected tool or appliance that breaker will not trip, and the exposed metal will remain energized.
  • Running an individual ground conductor back to the entrance panel and connecting it to the neutral bar or grounding strip. This is dangerous because the grounding conductor is not within the circuit cable or raceway. An individual conductor could eventually be damaged or removed for future repairs.

Installation of Low Voltage Equipment Without Proper Grounding: Another common grounding mistake, which is often found in low voltage equipment like satellite dishes, is that many of these devices are not grounded. They may not be fully compliant due to a grounding conductor that is long or small, they may have unlisted clamps at terminations, excess bands, or be connected to a single ground rod but not bonded to other system grounds all of which can result in fire hazards.

Satellite dishes, and other television and radio devices, contain an antenna discharge unit connected to the transmission line near where it enters the house. This antenna discharge must be grounded. The grounding conductor is usually copper. Aluminum or copper clad aluminum are as long as it is not in contact with masonry or earth, or within 18 inches of earth in outdoor applications.  

Grounding for CATV is slightly different since it is brought into the building via a coaxial cable, which contains a center conductor instead of an antenna discharge unit. Because of this, its very common for CATV grounding mistakes to occur. Here, the shield of the coaxial cable is connected to an insulated grounding conductor that is limited to copper but may be stranded or solid. For one or two family homes, the grounding capacitor should not exceed 20 feet in length.

Non-Installation of GFCI’s Where Required: Recent NEC Code editions call for the increased use of GFCI’s on all 125V single phase 15A and 20A receptacles in bathrooms garages accessory building with a floor storage, work and similar areas, outdoors, kitchens, laundry, utility and wet bar sinks and boathouses. Other areas that require the use of GFCIs include boat hoists, aircraft hangars, drinking fountains, cord and plug connected vending machines, fountains, commercial garages and more, as specified by the NEC handbook.

Improperly Connecting the Equipment Grounding Conductor to the System Neutral: The grounded neutral conductor must be connected to normally noncurrent carrying metal parts of equipment, raceways and enclosures through the main bonding jumper. Be sure to make this connection directly at the service disconnecting means. When a new entrance panel is purchased, a screw or bonding jumper will be included, as well as instructions for its installation, which is only to be performed if the panel is used as service equipment.

A major bonding jumper in a box used as a subpanel fed by a 4-wire feeder should also not be installed with a panel used as service equipment. Improper connection of this grounded neutral equipment can result in the presence of voltage in metal tools or appliance casings.

Improper Grounding Frames of Electric Ranges and Clothes Dryers: Before the 1996 version of the NEC handbook was released, a neutral could commonly be used as an equipment ground. However, today, we are commonly seeing a fourth wire being used, which is the equipment grounding conductor. Exceptions include existing branch circuit installations where an equipment grounding conductor is not present. Here, a new 4 wire branch circuit should be run from the panel. In the case of an old appliance, be sure to remove the neutral to fame bonding jumper if an equipment grounding conductor is to be connected.

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, workers would pull the pump and lay it on the ground to see if it would spin. In these instances, there was a likelihood that the case would become live due to a wiring fault. If this occurred the overcurrent device would not function, causing a shock hazard. Because of this, the NEC updated in 2008 to require a fourth equipment grounding conductor that must be lugged to the top of the well casing to prevent this from happening.

grounding mistakesFailure to Properly Attach the Ground Wire to Electrical Devices: Another common grounding mistake is wiring daisy chained devices in such a way that removing one of them will break the equipment grounding continuity. To avoid this, it is best to connect incoming and outgoing equipment grounding conductors to a short bare or green jumper. These should then be connected to the grounding terminal of the device.

Failure to Install a Second Ground Rod Where Required: If a single rod does not have a resistance to ground of 25 ohms or less, it should be augmented by a second rod. Once that second rod is installed, it’s not necessary for the two to meet the resistance requirement. Few electricians do the resistance measurement.

A simple ohmmeter can not be used for this measurement because doing so requires a known perfect ground. Special equipment and procedures are needed, so it’s common to drive a second ground rod. This must be located at least 6 feet from the first, although an even greater distance is preferred. If both rods and the bare ground electrode conductor that is connecting them are directly under the drip line of the roof, ground resistance will be further diminished due to the increasing moisture in the soil. The resistance will increase when the soil is dry.

Incorrect Method of Reattaching Metal Raceway Used as an Equipment Grounding Conductor: It is common that equipment ground paths are broken when equipment is relocated, replaced or removed for repair. If these connections are not fixed, it can result in a a fire hazard. This is why every measure should be taken to make sure setscrews, locknuts and threads are fully engaged and continuity tests should be performed before equipment is put back into service. Dirt and corrosion can also compromise ground continuity.

The NEC mandates that all electrical equipment, wiring, and electrically conductive material should be installed by creating a low impedance circuit from any point on the wiring system to the electrical supply source to facilitate the operation of overcurrent devices.

Failure to Bond Equipment Ground to Water Pipe: Improper connections are commonly seen in electrical field. Screw clamps and other improvised connections do not provide permanent, low impedance bonding. It’s also a bad idea to simply wrap wire around the pipe or omit the bonding completely.

If working in a dwelling, a conductor should run to a metallic water pipe and connect with a UL listed grounding clamp. The bonding conductor’s size should be based on the size of the largest ungrounded service entrance conductor or equivalent area for parallel conductors.

Although electrical grounding is an important safety measure, its purpose can easily be defeated by making these common grounding mistakes. If you are a professional working with electrical equipment, it is important to stay updated with the latest NEC regulations to make sure your installations and repairs are done safely and up to code. That way, you can be sure that the gear you work with will not cause any electrical hazard for those that come into contact with it.