frame of a portable generator need not be

grounded (connected to earth) and that the

frame may serve as the ground (in place of

the earth):

• The generator supplies only equipment

mounted on the generator and/or cordand plug-connected equipment through

receptacles mounted on the generator, 

§ 1926.404(f)(3)(i)(A), and

• The noncurrent-carrying metal parts of

equipment (such as the fuel tank, the internal combustion engine, and the generator’s

housing) are bonded to the generator

frame, and the equipment grounding conductor terminals (of the power receptacles

that are a part of [mounted on] the generator) are bonded to the generator frame, 

§ 1926.404(f)(3)(i)(B). 

Thus, rather than connect to a grounding

electrode system, such as a driven ground

rod, the generator’s frame replaces the

grounding electrode.

If these conditions do not exist, then a

grounding electrode, such as a ground rod,

is required. 

If the portable generator is providing electric

power to a structure by connection via a

transfer switch to a structure (home, office,

shop, trailer, or similar) it must be connected

to a grounding electrode system, such as a

driven ground rod. The transfer switch must

be approved for the use and installed in

accordance with the manufacturer’s installation instructions by a qualified electrician.

Major Causes of Injuries and Fatalities

• Shocks and electrocution to users from

improper use. 

• Shocks and electrocution to utility workers

from improper connection to structures, such

as residences, offices, shops and trailers.

Safe Work Practices 

• Maintain and operate portable generators

in accordance with the manufacturer’s use

and safety instructions. 

• Never attach a portable generator directly

to the electrical system of a structure

(home, office or trailer) unless the generator has a properly installed open-transition

transfer switch. 

• Always plug electrical appliances and tools

directly into the generator, using the appliance manufacturer’s supplied cords. Use

heavy-duty extension cords that contain a

grounding conductor (3-wire flexible cord

and 3-pronged cord connectors).

• Proper grounding and bonding are a means

to prevent shocks and electrocutions.

• Use ground-fault circuit interrupters (GFCIs)

as per the manufacturer’s instructions.

• Do not connect a generator to a structure

unless the generator has a properly

installed transfer switch.

• Visually inspect the equipment before use;

remove defective equipment from service;

mark or tag it as unsafe for use.

Grounding Requirements for Portable

and Vehicle-mounted Generators

Under the following conditions, OSHA

directs (29 CFR 1926.404(f)(3)(i)) that the

FactSheet

Grounding Requirements 

for Portable Generators

Portable generators are internal combustion engines used to generate electricity.

They are useful when temporary or remote power is needed, and are commonly

used during cleanup and recovery efforts following disasters. 
Grounding requirements for generators connected via transfer switches are covered by

Article 250 of the National Electrical Code

(NEC). 

Safe Work Practices for Portable Tools

include:

• Do not use underrated cords—replace

them with appropriately rated cords that

use heavier gauge wires.

• Never use electrical tools or appliances

with frayed cords, missing grounding

prongs, or damaged or cracked housings. 

• Use double-insulated tools and equipment

distinctively marked as such, where possible. 

• Use battery-operated tools, where possible.

Verification by Testing

The integrity of the connection between the

generator’s frame and the equipment

grounding terminals of power receptacles is

important to the safe use of the equipment.

The connection may be confirmed via testing

by a competent electrician with the correct

This is one in a series of informational fact sheets highlighting OSHA programs, policies or 

standards. It does not impose any new compliance requirements. For a comprehensive list of 

compliance requirements of OSHA standards or regulations, refer to Title 29 of the Code of Federal

Regulations. This information will be made available to sensory impaired individuals upon request.

The voice phone is (202) 693-1999; teletypewriter (TTY) number: (877) 889-5627.

equipment. The ohmic resistance should

measure near zero and must not be intermittent, which indicates a loose connection.

Bonding Versus Grounding

Bonding and grounding are separate requirements for generators and other electrical distribution systems. Grounding means the connection, or the establishment of a connection, of an electric circuit or equipment to reference ground, which includes the generator’s frame. Bonding is the intentional connection between the grounded circuit conductor (neutral) and the grounding means for

the generator, which includes the generator’s

frame. Thus, effective bonding of the neutral

conductor to the generator’s frame is also a

concern for the safe use of the equipment. As

with grounding terminal connections, proper

bonding of the neutral terminal of a power

receptacle may be confirmed via testing by a

competent electrician with the correct equipment, and the ohmic resistance should measure near zero and must not be intermittent,

which indicates a loose connection.

U.S. Department of Labor

www.osha.gov

(800) 321-OSHA

For more complete information:

DSTM 10/2005