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The Safe Use of Extension Cords in the Lab

Used in the office, in the lab, and in the field, taken for granted until you need one. What are we talking about? Electrical extension cords

Vince McLeod, CIH

Vince McLeod is an American Board of Industrial Hygiene-certified industrial hygienist and the senior industrial hygienist with Ascend Environmental + Health Hygiene LLC in Winter Garden, Florida. He has more...

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An Indispensable Tool Requiring Serious Safety Consideration

Essential to modern life and a familiar part of our surroundings, yet often not treated with deserved respect. Run over, walked on, crimped in windows and doors, left out in sun and storm alike, strung together, bent, yanked, and strung across rooms and under carpets, strewn across wet grass and through holes in walls, taped up and snarled in tangles that would give a sailor nightmares. Used in the office, in the lab, and in the field, taken for granted until you need one. What are we talking about? Electrical extension cords, one of the most indispensable tools we use today, but too often with little consideration. And, sometimes used in a fashion that could have disastrous results.

In 1997, more than 12,000 people were treated for electrical shocks and burns; about 2,500 of them were treated for injuries stemming from extension cords.1 In addition, each year about 4,000 injuries associated with electric extension cords are treated in hospital emergency rooms. Half of these injuries involve fractures, lacerations, contusions, or sprains from people tripping over extension cords. Roughly 3,300 home fires originate in extension cords each year, killing 50 people and injuring about 270 more.2 However, with a little care and some precautions, these conveyors of power can be used safely.

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Related Article: Electrical Safety in the Lab

We must caution up front, that if you have more than a few extension cords powering equipment in your lab, it is probably time to either call an electrician to install additional strategically placed outlets, or to rearrange equipment. Likewise, if you have any cords running through walls, up through the ceiling and down somewhere else, an electrician is definitely required. Extension cords should only be used when necessary and only for temporary use. You should always plug equipment directly into a permanent outlet when possible. Where this is not possible, however, you should begin by selecting the right cord for the job.

Indoors or outdoors, the use of extension cords serve different needs and should be selected accordingly. Regardless of location, always use the three-prong type of cord approved for either indoor or outdoor use. In addition, the cord should have a certification label from an independent testing lab such as UL (Underwriters Laboratories) or ETL (Electrical Testing Laboratories) on the package and attached to the cord near the plug.

The amount of current a cord can handle will depend on the diameter of the conductors (copper wire part of the cord). Cords that contain more copper can safely handle more power. The wire size is measured by the gauge of the wire. You will usually find numbers like 16, 14, or 12 gauge on an extension cord package and the cord itself. Now, this is one of those confusing issues. You would think that a 16-gauge wire is bigger than a 12-gauge wire, but it’s not! As the number gets smaller, the thickness of the conductor gets bigger. A 12-gauge wire can safely carry much more power than a 16-gauge wire. Compare the capacity on the label to the intended load.

Always use the shortest extension cord possible, to minimize risk of damage to the cord and reduce electrical resistance across the length of the cord. Extension cords, by the nature of their length and conditions of use, are much more prone to damage than other types of wiring. It is important to check the total length of the cord for damage before putting it into use.

One should start by looking at the ends of the cords. The male end—the end with the three prongs that fit into an electrical outlet—is the one that is most prone to damage. The two flat power-conducting prongs are subject to bending, while the round prong (often called the ground pin), can be broken off. Without the ground pin there is no path to ground through the wires—potentially a very dangerous situation.

Outdoor use extension cords, and many equipment cords, have a tough outer layer designed to protect the inner wires. If the outer jacket is damaged, the softer inner insulation around the wires can easily become damaged as well. Does this mean you should whip out the tape to repair it? No, damage to an extension cord jacket, or any cord for that matter, should never be fixed by wrapping it with tape. Even electrical tape does not have sufficient strength or abrasion resistance to make a permanent repair as required by OSHA. A taped-up extension or power cord to a piece of equipment is an easy OSHA citation.

So, what to do if you have a damaged cord? If the damage is extensive, cut off the plug and throw it out. Replace it with a new cord. Alternatively, the cord can be cut at the point of damage and a new plug installed. Too many times, especially if the female end is damaged, we see outlet boxes intended for structural use installed on the extension cord. These are not permitted if the box is designed to be surface mounted. The clues to easy identification are indentations (knockouts) on the side about the size of a nickel and small holes on the back. Instead, use hard-walled outlet boxes that are approved for use on a flexible cord.

Related Article: Require Grounded Plugs on All Electrical Equipment

Next, where to plug it in? If you are outside, or in a wet or damp location, or near water, look for outlets protected by Ground Fault Circuit Interrupters (GFCIs). A GFCI is a fast-acting device that detects small current leakage from electrical equipment. In other words, it senses electricity traveling to ground via something other than the wires, such as yourself. It shuts off the electricity within 1/40th of a second if sufficient current leakage is detected. It provides effective protection against shocks and electrocution. GFCI pigtails—very short cords with a GFCI built in—can be used with plug and cord equipment in areas without protected outlets. Although GFCI outlets are required by building codes for bathrooms, kitchens, rooftops, and garages, they are not always required near laboratory sinks. This requirement varies by locale and code enforcement authority. We think, however, it is a good idea, and almost always recommend them on outlets within six feet of laboratory sinks.

Special cases, such as in pits, tanks, or near certain manufacturing processes where flammable materials are used, require special electrical equipment designed such that they will not be possible ignition sources. This equipment carries the designation “intrinsically safe.” Only intrinsically safe equipment may be used in these potentially explosive areas.

Before closing, here are OSHA’s actual rules:3

  • 1910.305(g)(1)(iii) Unless specifically permitted in paragraph (g) (1)(i) of this section, flexible cords and cables may not be used:
  • 1910.305(g)(1)(iii)(A) As a substitute for the fixed wiring of a structure;
  • 1910.305(g)(1)(iii)(B) Where run through holes in walls, ceilings, or floors;
  • 1910.305(g)(1)(iii)(C) Where run through doorways, windows, or similar openings;
  • 1910.305(g)(1)(iii)(D) Where attached to building surfaces; or
  • 1910.305(g)(1)(iii)(E) Where concealed behind building walls, ceilings, or floors.

Remember, when using electrical equipment, look for an outlet you can plug directly into. If that is not possible, choose the right cord, and make sure it is in good shape and protected from damage while in use. And please, use GFCI-protected circuits when outdoors or in wet locations.


1. 2001 Electrocutions Associated with Consumer Products, Consumer Product Safety Commission. Bethesda, MD. 2004. 

2. Extension Cord Safety, Electrical Safety Foundation International. Arlington, VA. 2015. 

3. Wiring methods, components and equipment for general use. Occupational Health and Safety Administration. Washington, D.C.