Staying grounded

Safely ground electricity when arc welding

PRACTICAL WELDING TODAY® MARCH/APRIL 2006

March 7, 2006

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Because a typical arc welding setup may consist of several electrical circuits, it's critical to apply and maintain proper grounding methods within the welding area to promote electrical safety in the workplace.

Grounding means much more than punishing your teenager by restricting his privileges. In welding, grounding is critical to arc welding safety.

Various codes and standards document grounding electrical circuits as a safety practice. A typical arc welding setup may consist of several electrical circuits. Applying and maintaining proper grounding methods within the welding area are important to promote electrical safety in the workplace. Associated processes such as plasma cutting also benefit from proper grounding.

Welding Machine Grounding

Welding machines that use a flexible cord and plug arrangement or are wired permanently into an electrical supply system have a grounding conductor. The grounding conductor connects the metal enclosure of the welding machine to the ground. If you could trace the grounding wire back through the electrical power distribution system, you would see that it's connected to earth, usually through a metal rod driven into the ground.

Connecting the equipment enclosure to the ground ensures that the machine's metal enclosure and ground are at the same potential. When they're at the same potential, you won't get an electrical shock if you touch the two points. Grounding the enclosure also limits the voltage on the enclosure in case the equipment's insulation fails.

The grounding conductor's current-carrying capability is coordinated with the electrical supply system's overcurrent device. This coordination allows the grounding conductor to remain intact even if an electrical fault occurs within the welding machine.

Some welding machines have a double-insulated design; these don't require a grounding conductor connection. Instead, they rely on extra insulation to protect you from shock. When present, double insulation is identified by a "box within a box" symbol on the rating plate.

For small welding machines that use a plug on the end of a power cord, the grounding conductor connection is made automatically when the welding machine is plugged into the receptacle. The grounding pin of the plug makes a connection within the receptacle. It's not recommended that you use an adapter that effectively removes the grounding pin connection at the plug. Also, it's suggested that you don't cut off or remove the grounding pin from the plug. Without the connection, all safety benefits of the grounding conductor are lost.

Figure 1
Receptacle circuit testers allow you to verify whether the grounding circuit is available at the outlet.

Periodically you should test your receptacle circuit to check the continuity of the grounding conductor. You can buy receptacle circuit testers for 120-volt circuits at electrical supply or hardware stores; they are inexpensive and plug into an electrical outlet (see Figure 1). Indicator lights show whether the grounding circuit is available at the outlet, as well as other circuit tests. If the test device shows that you're missing a ground connection or have a circuit problem, call a qualified electrician for assistance. Likewise, consult a qualified electrician to test circuits greater than 120 V.

Workpiece Grounding

The welding circuit consists of all conductive material through which the welding current is intended to flow (see Figure 2). Welding current flows through the welding machine terminals, welding cables, workpiece connection, gun, torch, electrode holder, and the workpiece. The welding circuit isn't connected to ground within the welding machine, but is isolated from the ground.

Figure 2
The welding circuit flowing through the welding machine, work lead, and welding arc is isolated from ground in the welding machine.

According to American National Standards Institute (ANSI) Z49.1, "Safety in Welding, Cutting and Allied Processes," the workpiece or the metal table that the workpiece rests on must be grounded. You must connect the workpiece or work table to a suitable ground, such as a metal building frame. The ground connection should be independent of or separate from the welding circuit connection.

Grounding the workpiece has similar benefits to grounding the welding machine enclosure. When the workpiece is grounded, it's at the same potential as other grounded objects in the area. In the event of insulation failure in the welding machine or other equipment, the voltage between the workpiece and ground will be limited. Note that it's possible to have an ungrounded workpiece, but this requires the approval of a qualified person.

The workpiece connection isn't a ground clamp. The workpiece is connected to a welding cable, typically by means of a spring-loaded clamp or screw clamp.

Unfortunately, many welders call a workpiece connection a "ground clamp," and the workpiece lead a "ground lead." The welding cable doesn't bring a ground connection to the workpiece. The ground connection is separate from the workpiece connection (see Figure 3).

Figure 3
The work cable does not bring a ground connection to the workpiece. Instead, it only serves to complete the welding circuit.

High-frequency Grounding

Some welding machines use starting and stabilizing circuits that contain high-frequency voltage. This is common on gas tungsten arc welding (GTAW) machines. The high-frequency voltage may have frequency components that are in the megahertz range. In contrast, the welding voltage may be as low as 60 Hz.

High-frequency signals tend to radiate away from the welding area. These signals may cause interference with nearby radio and television reception or other electrical equipment. One way to minimize high-frequency signal radiation is to ground the welding circuit. The welding machine instruction manual includes specific instructions on how to ground the welding circuit and components in the surrounding area to minimize the radiation effect.

Portable and Vehicle-mounted Welding Generator Grounding

Portable and vehicle-mounted arc welding generators often can supply 120- and 240-V auxiliary power. These generators are used in remote locations away from an electrical power distribution system. A convenient earth ground usually isn't available for connection.

When asking yourself whether or not the generator frame should be grounded, consider that the rules for grounding depend on the specific use and design of the auxiliary power generator. Most applications fall into one of two categories:

1. You are not required to ground the generator frame if all of these requirements are met:

  • The generator is mounted to a truck or trailer.
  • The auxiliary power is taken from receptacles on the generator using a cord and plug arrangement.
  • The receptacles have a grounding pin.
  • The frame of the generator is bonded, or electrically connected, to the truck or trailer frame.

2. You are required to ground the generator frame if either of these conditions are met:

  • The generator is connected to a premises wiring system; for example, if it supplies power to a house during a blackout.
  • The auxiliary power is hard-wired into the generator without using cords and plugs.

You should consult your local electrical codes and ANSI/National Fire Protection Agency (NFPA) 70, "National Electrical Code," for more details.

Extension Cord Grounding

Test extension cords periodically for ground continuity. Extension cords lead a rough life while lying on the ground; they're underfoot and prone to damage. A receptacle circuit tester will confirm that all of the connections are intact within the cord, plug, and receptacle.

Welding Circuit Shock Hazards

Proper grounding in the welding environment is good practice, but it doesn't remove all possibility of electrical shock. The welding circuit is energized by welding voltage. You will receive a shock if you become the electrical path across the welding circuit. Take precautions to insulate yourself from the welding circuit by wearing dry insulating gloves and other insulating equipment. Also maintain insulation on weld cables, electrode holders, guns, and torches to provide protection.

You also can prevent electric shock originating from the electrical supply system. Maintaining electrical equipment and extension cords will insulate you from electrical sources.

Frank Stupczy is compliance engineering manager for The Lincoln Electric Co., 22801 St. Clair Ave., Cleveland, OH 44117, 216-481-8100, fax 216-486-1751, www.lincolnelectric.com.



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