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Safety and HealthFact Sheet No. 29 April 2014 © 2014 American Welding Society

GND/PE

Grounding of Portable and Vehic le Mounted WeldingGenerators

American Welding Society8669 Doral Blvd.Doral, Florida 33166E-mail: [email protected]://www.aws.org

Fact Sheet No. 29 – 04/14

AWS disclaims liability for any injury to persons or to property, or other damages of any naturewhatsoever, whether special, indirect, consequential or compensatory, directly or indirectlyresulting from the publication, use of, or reliance on this information. AWS also makes noguaranty or warranty as to the accuracy or completeness of any information published herein.

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INTRODUCTION

Proper grounding and bonding of portableand vehicle mounted welding generatorsthat also supply 115 or 230 volts ACauxiliary power is an on-going topic amongwelders. This Fact Sheet will help youdetermine the requirements for bondingand grounding welding generators.

Additionally, it will give definitions andpresent necessary electrical concepts toclarify the requirements for bonding andgrounding.

TERMS

Sources: ANSI Z49.1, hereafter termedZ49.1, AWS A3.0, and NEC--NationalElectrical Code, hereafter termed NEC.See Information Sources Section at end for

details.

Bonding —The permanent joining ofmetallic parts to form an electricallyconductive path that will ensure electricalcontinuity and the capacity to conductsafely any current likely to be imposed.

Ground —The electrical potential of theearth’s surface; a conducting connection,whether intentional or accidental, between

an electrical circuit or equipment and theearth, or to some conducting body thatserves in place of the earth.

Ground Connection —An electricalconnection of the welding machine frameto the earth for safety.

Grounded —Connected to earth or tosome conducting body that serves in placeof the earth.

Grounded, effectively —Intentionally

connected to earth through a groundconnection of sufficiently low resistanceand with adequate current-carryingcapacity to prevent the buildup of voltagethat may be hazardous to connectedequipment or to persons.

Grounding —The process of bonding oneor more conductive objects to the ground,so that all objects are at zero (O) electricalpotential; also referred to as “earthing.”

Grounding Conductor —A conductorused to connect equipment or thegrounded circuit of a wiring system to agrounding electrode or electrodes [groundrod(s) or metal water pipe].

Ground Rod —A metal rod, typicallycopper, not less than eight feet in lengthand 1/2 inch in diameter, driven into theearth such that at least eight feet of length

is in contact with the soil, to function as asuitable connection point to earth. NOTE:Since different diameters are required fordifferent rod materials and the drivenlength and number of rods used depends

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on the special soil conditions andapplications, consult the NEC for thespecific data for the correct ground rod andmethod of use for each particular situation.

Hard Wired —Connected by separate

conductors to a junction point or box—notto receptacles.

Metal Water Pipe —Typically anunderground metal water pipe that supplieswater to a building or premises or faucet/outlet and that is in contact with the earthfor a specified distance. NOTE: Since themetal water pipe has several keyrequirements that must be met before itcomplies with regulations, consult the NEC

for specific information before selectingany pipe for a ground connection.

Portable —Capable of being carried ormoved about; designed for readymovement and use in field locations.

Separately Derived System-- A premiseswiring system whose power is derived froma battery, a solar photovoltaic system, orfrom a generator, transformer, or converter

windings, and that has no direct electricalconnection, including a solidly connectedgrounded circuit conductor, to supplyconductors originating in another system.

Vehicle Mounted —Equipment installed ina truck, trailer, or similar wheeled vehicle.

Work —The workpiece or metal uponwhich the welder welds and is normallygrounded independently of the welding

leads to a good electrical ground unless aqualified person assures it is safe to workon an ungrounded workpiece.

Work Lead —The electric conductor be-tween the source of arc welding currentand the work. The work lead should not bereferred to as the ground lead. It ispreferable to connect the work lead directlyto the work. Unless a separate groundingconductor is used (to connect the

workpiece to an earth ground), the worklead will not be grounded.

NATURE OF THE HAZARD

Some basics:

When the generator is running,current can pass through a wire, aladder, a hoist, your body, or anyother conductor.

If you become part of an electricalcircuit, current can pass throughyour body causing a shock.

Why Grounding is Important: Groundingthe frame of electrical equipment ensuresthe following:

Generators are grounded to preventthe buildup of voltages that may

result in undue hazards to personsor equipment.

When no voltage difference existsbetween the grounded generatorframe and earth, no electric currentcan flow. Therefore, the shockhazard is reduced.

Since it is the flow of electric currentthrough the human body that is

hazardous, proper grounding is oneof the best ways to preventunintended electric shock

.

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If we don’t ground the generator andshould have, the results can behazardous—here’s why:

If the auxiliary power circuit has afault condition (such as a shortcaused by bare wires), and there isno safety ground connection toprotect the user, the result can bean electric shock.

Additionally, grounding helpsprevent possible fire or explosionwhen fueling by reducing thechances for static electricity sparks

from the fuel nozzle to the tank.

CONDITIONS WHERE GROUNDING THEGENERATOR FRAME TO A METALWATER PIPE OR GROUND ROD ISREQUIRED BY THE NEC:

1. The welding generator is not part of aseparately derived system, OR

2. It has its neutral conductor solidly

interconnected to a service-suppliedsystem neutral, OR

3. It supplies auxiliary power output (115volts AC / 230 volts AC) by means otherthan cord-and-plug connection throughreceptacles mounted on the generator,such as connections to internal terminalson the generator—hard wired (seeequipment Owner’s Manual for groundinginstructions).

When ANY of these conditions are met,grounding is required.

CONDITIONS WHERE GROUNDING THEGENERATOR FRAME TO A METALWATER PIPE OR GROUND ROD IS NOTREQUIRED BY THE NEC:

1. The welding generator has auxiliarypower output (115 volts AC or 230 volts

AC) and the generator receptacles have aground pin outlet available for theequipment that plugs into the receptacle,

AND

2. The generator is portable or mounted ona truck or trailer, AND

3. The auxiliary power is used by cord-and-

plug-connection means through recep-tacles mounted on the generator, AND

4. The generator is mounted on a vehicleand the generator frame is bonded to thevehicle frame.

HOW TO AVOID THE HAZARDS

Follow the manufacturer’s recom-mended procedures for grounding

the welding generator.

Watch out for bed liners in trucks— securely connect the weldinggenerator frame to the frame of thevehicle or trailer by a ground wire orbolted metal-to-metal contact.

Bond the generator to the vehicleframe or earth.

When grounding a generator sittingdirectly on the earth, use a drivenground rod to ensure the earthconnection.

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Keep the fuel nozzle in contact withthe tank when fueling to preventstatic sparks and fire

SUMMARY

Proper grounding of the weldinggenerator frame can help preventelectric shock.

If your generator is in a truck ortrailer, and you use power directlyfrom the receptacles via plugs,connect (bond) the generator frameto the vehicle frame—be sure thereis a good metal-to-metal connection.

If you hard wire the generatorauxiliary power to a project orbuilding electrical system, then youmust connect the generator frame toa driven ground rod or metal waterpipe.

The decision is based on whatyou do with your auxiliary power: If you just plug equipment into the

receptacles, connection to thevehicle frame is fine. If you hardwire the auxiliary power into anotherelectrical system, then you mustconnect the generator frame to adriven ground rod or metal waterpipe.

Remember: The objective is tokeep the frame of the generator atzero (or earth) voltage.

In simplest terms, grounding thewelding generator frame providesan electrical path to ground instead

of a possible electrical shock hazardto the user.

INFORMATION SOURCES

American National Standards Institute(ANSI). Safety in Welding, Cutting, and

Allied Processes, Z49.1, available from American Welding Society, 8669 DoralBlvd., Doral, FL 33166; Web site:www.aws.org.

Occupational Safety and Health Administration (OSHA). Code of FederalRegulations, Title 29 Labor, Part 1910,available from the U.S. GovernmentPrinting Office, 732 North Capitol StreetNW, Washington, DC 20401; telephone:

800-321-6742; Web site: www.osha.gov.

National Fire Protection Association(NFPA). National Electrical Code (NFPA70), available from National Fire Protection

Association, 1 Batterymarch Park, P.O.Box 9101, Quincy, MA 02269–9101;telephone: 800–344–3555; Web site:www.nfpa.org.

Institute of Electrical and Electronic

Engineers (IEEE), IEEE RecommendedPractice for Grounding of Industrial andCommercial Power Systems —Green Book,ISBN 1-5593-7141-2, Product NumberSH14498-TBR Standard 142-1991,avail-able from IEEE Publications Office, 10662Los Vaqueros Circle, P.O. Box 3014, Los

Alamitos, CA 90720-1264; telephone: 800-272-6657; Web site: www.ieee.org .

American Welding Society (AWS). Welding

Terms and Definitions (AWS A3.0),available from American Welding Society,8669 Doral Blvd., Doral, FL 33166; Website: www.aws.org.

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