by , on May 31, 2016

Electrical cords and extension cords are common everywhere. From homes to the workplace, they are one of the most commonly used and most likely abused tool that we have.

Often utilized for simple things like plugging in the space heater at work or stringing decorative lights during holidays, the easiest option for consumers is to go online or to the nearest hardware section of a store and purchase an inexpensive cord. If the price, length of cord and type of connector meet our needs, we will likely purchase the item and not think anything else about it.

Choosing an extension cord is more involved than that.

Before buying an extension cord, plan ahead. Know what it will be used for and where it’s going to go. It’s also important to know how much power the equipment you’ll be plugging into it uses.

IEEE has an informational paper that describes what to do and NOT to do with electrical equipment cords and extension cords. Here are a few examples:

  • DON’T plug extensions cords together.
    • Get one that is the correct length you need. It may be tempting to just string them together, but resist the temptation. Extending the length of an extension cord by “daisy-chaining” can lead to overheating the cord by overloading it, creating a serious fire hazard.
  • DON’T exceed the rating of the cord.
    • This is a common mistake in offices that allow space heaters. All extension cords have wattage limits, and these limits must be respected. Again, you are looking at a fire hazard if the cord is overloaded. Some of the cheaper extension cords use internal wiring that is size 16 gauge, rated for only 10 amps. A typical 1500 watt space heater will draw 12.5 amps, obviously overloading a 16-gauge extension cord. To be safe, plug the heater directly into the wall and skip the extension cord or power strip altogether.
  • DON’T allow the cords to become a trip hazard.
    • Spending a little extra up front on a cord that is longer but able to be stored out of the way of foot traffic is better than having someone injure himself or herself because of tripping over the cord. However, do not use metal staples or nails to secure a temporary power cord. Keep in mind that the National Electrical Code does not allow extension cords in lieu of permanent wiring (NEC 400.8(1) – 2014 Version). See this OSHA section (specifically 1910.305(g)(1)(iv)) for other restrictions as well as the following OSHA interpretation letter for more guidance. Another good interpretation letter can be found here.

And my personal favorite:

  • DON’T use extension cords to connect wires in the attic/above suspended ceilings/ANYWHERE.
    • These are just accidents waiting to happen. A common violation is found in the installation of ceiling-mounted electrical equipment like projectors in training and meeting rooms (as in the following photo). These locations must have a receptacle mounted flush with the ceiling with the unit’s power cord visible at all times.

Projector

See IEEE’s complete list.

National Electrical Safety Month

e-Hazard understands that choosing to be electrically safe is a daily, ongoing habit. Make improvements where you know there is a potential problem, become educated, and make wise decisions every day.

Our 40-hour 2014 National Electrical Code course can train your electrical personnel to stay current with all of the electrical requirements in your facility. As we say in our electrical training classes, each person is ultimately responsible for his or her safety.


Ken Sellars
About author:
Ken Sellars is an instructor of electrical safety, NEC, Grounding/Bonding and Arc Flash Safety courses nationwide. Read more about Ken.

25 Comments on "Electric Safety: 4 Common Mistakes Using Extension Cords"

Liko - 20 May 2017 Reply

Thank you. Just the information I was searching for.

    Ken Sellars
    Ken Sellars - 22 May 2017 Reply

    You are welcome. I'm glad we could be of assistance!

Danielle - 31 May 2017 Reply

Hello there! Is it ok to plug an extension cord in a power cord?

    Ken Sellars
    Ken Sellars - 12 June 2017 Reply

    If you are asking if it is okay to plug one extension cord into another extension cord, the general answer is that it is not a good idea. Each cord length has a specific ampere rating based upon the cord's internal wiring size and distance of those wires. If you add another in-line, you could easily exceed the allowed or desired voltage drop on the circuit, causing a lower-than-standard voltage on the receptacle-end of the cord. This could result in a low supply voltage to the device being utilized, and this condition could cause equipment failure and present a fire hazard as well. It is recommended to always purchase the length of cord that is needed for your application, and then be sure to not overload the cord. The rating is required to be included on the cord per the listing agency's mandate. I always recommend that you purchase the largest-size cord that you can afford to minimize effects of voltage drop and to be able to provide the most wattage as safely possible on the receptacle end. By following this practice, the equipment being utilized will last longer and you will minimize unnecessary risks of fire. And do not forget to use GFCI-protection on the SUPPLY end of your extension cord - a critical link in the electrical safety chain!

Debbie Keys - 16 January 2018 Reply

I'm looking for clarification/interpretation of the National Electrical Code's prohibition of use of extension cords in lieu of permanent wiring (NEC 400.8(1) – 2014 Version). I do not see the referenced OSHA interpretation letter. How is "permanent wiring" defined?

    Ken Sellars
    Ken Sellars - 22 January 2018 Reply

    My sincere apologies. Somehow the links either disappeared from the article or were overlooked when the article was released. Either way, they are now restored. The most important restriction is listed in OSHA 1910.305(g)(1)(iv) and states (partial quote): 1910.305(g)(1)(iv) Unless specifically permitted otherwise in paragraph (g)(1)(ii) of this section, flexible cords and cables may not be used: 1910.305(g)(1)(iv)(A) As a substitute for the fixed wiring of a structure; 1910.305(g)(1)(iv)(B) Where run through holes in walls, ceilings, or floors; 1910.305(g)(1)(iv)(C) Where run through doorways, windows, or similar openings; 1910.305(g)(1)(iv)(D) Where attached to building surfaces; 1910.305(g)(1)(iv)(E) Where concealed behind building walls, ceilings, or floors; or 1910.305(g)(1)(iv)(F) Where installed in raceways, except as otherwise permitted in this subpart. To be specific to your question, the idea or definition of "permanent wiring" is referred to in 400.8 of the 2014 NEC as "fixed wiring," referring to the previous "Uses Permitted" section in 400.7. Basically, if you have uses OUTSIDE of 400.7, then flexible cords or cables should NOT be used in this application. Anything outside of these allowances would have to be approved by your Authority Having Jurisdiction, which usually would be the city/county/state electrical inspector, or the Federal version of this on any Federal properties. To be transparent, the term "permanent" is not well defined in the NEC, but the wording "fixed wiring" is intended to mean normal building wiring, as in conductors in raceways, cable trays, or building cable designed for that purpose. I hope this clears things up a little. If not, please let me know.

Hilton Homes - 19 March 2018 Reply

Your tips are very helpful! It was so informative and it really does help people especially since a lot of people tend to plug extension cords together! Thanks for this information.

    Ken Sellars
    Ken Sellars - 3 April 2018 Reply

    It is critical to stay on top of electrical safety, even with things like extension cords and power strips. Thanks for your kind comments.

Tim - 9 April 2018 Reply

If one complies to all the safety recommendations associated with use of extension cords, why is it unsafe to run an extension cord in the attic?

    Ken Sellars
    Ken Sellars - 16 April 2018 Reply

    In general, all cables have heat restrictions and overall use restrictions. Attics can get very hot, and extension cords may not be rated for this type of heat, which could cause the cable insulation to break down prematurely and would be a fire risk. Also, you must look at the manufacturer's use restrictions in accordance with its listing and labeling and only use extension cords per the manufacturer's allowance. One more point - an extension cord is never meant to be used in the place of permanent wiring provisions. The idea of a cord is for temporary power only. If I am using one in an attic, it sounds as if a receptacle should be permanently installed near the equipment needing the power. This is a much safer installation in general.

Jonathan - 16 April 2018 Reply

what if i'm hooking up an alarm device like this, https://www.amazon.com/gp/product/B0006BCCAE/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1 , https://www.amazon.com/BINZET-Transformer-120V-130V-Convertor-Regulator/dp/B00JRX360W/ref=pd_rhf_ee_p_img_14?_encoding=UTF8&psc=1&refRID=2CTJNQFBZKWG47PD4BDN . I was planning on having it hooked up to a back up battery source in the garage (upc) for security reasons but was gonna have an extension cord connecting them. Is there any other way? I don't think its a good idea to put a backup battery in the attic, but that seems like the only other option. would that be safe?

    Ken Sellars
    Ken Sellars - 16 April 2018 Reply

    Extension cord is not the answer. You can get rated wiring for this at any electrical supply store. Ask for security/fire alarm wire and they can give you a 2-wire cable made just for this purpose. Run this from your UPS DC output to your alarms. This will be a code-compliant installation.

Jonathan - 16 April 2018 Reply

I appreciate that information, Thank you

BRIAN FERBER - 5 July 2018 Reply

Hello. Can you plug an extension cord into a water cooler? Where is there a definition of "portable" to determine whether those bottled water machines delivered are considered portable/ Thanks

    Hugh Hoagland
    Hugh Hoagland - 12 July 2018 Reply

    The reasoning for NOT using an extension cord is fire and voltage drop. While the water cooler is "technically portable", you are not moving it around and plugging and unplugging the cord regularly. In that case it should be a permanent plug. This eliminates two possible failed connections that could cause shock or fire over time. If it is being moved, be sure the cord is adequately protected and that it can carry the current. The goal of the NEC is to prevent shock and fire (NFPA is primarily a firefighter's organization).

David - 1 August 2018 Reply

I want to run a small device in my attic, using 2 Watts or less. Would a power strip or extension lead still be unwise? I can't think of any other way to power it.

    Hugh Hoagland
    Hugh Hoagland - 2 August 2018 Reply

    This is not allowed via the NEC. I would never do this since it is a potential fire hazard IF the power strip fails. According to NFPA, failed power strips are one of the number one causes of house fires. The best way is to a licensed electrician install a plug or direct wire the device. Anything in the attic is heavily stressed due to temperature changes and should be VERY high quality and designed for that use.

Richard W Dyer - 13 August 2018 Reply

Hey Hugh, Great article but I still have a question. Working construction, in a large building, is it daisy chaining to use a short GFCI plug (12-18 inches) between a non-GFCI building outlet and an extension cord that is being used to power HEPA air scrubbers, lights, fans, and or power tools? Also, I read in the HEPA air scrubbers add on Amazon that because there is a fuse or GFCI inside the scrubber, they can be daisy chained. Is this true? If so then can a GFCI line cord be used between more than one extension cord?

Joe Dirt - 16 January 2019 Reply

This article is written and rules like this were put into place to get the NECA contractor's more work. Plain and simple. If you really worked construction and knew the actual challenges and didn't just sit at a desk and think of ways to get more work for your members, you would know this. There is nothing wrong with plugging two extension cords into each other as long as the load and voltage changes are considered while doing it. We are qualified and certified professionals on the job. To say you can only use one extension cord is nonsense.

    Ken Sellars
    Ken Sellars - 17 January 2019 Reply

    Joe, we are not involved with NECA (although I highly respect them as an organization), so I am not sure where that comment comes from. I have in fact worked construction for many years, and was a licensed electrical contractor for many years. I still hold a Master's Electrical license just in case I ever have to go back to my tools. I have worked industrial, military, utility, and commercial electrical work, in construction, maintenance, repair - just about all facets of the electrical trade. By you stating that you are "qualified and certified", and then continuing on to say that you can plug one extension cord into another, you may want to consider important things like product listing/labeling requirements, and the National Electrical Code section 110.3(B), which requires people to follow listing/labeling requirements. UL 817 is the standard for evaluating cord sets and power supply cords, or what we call "extension cords." The idea of daisy-chaining directly violates one of the required markings on such cords, that is required to state, "Do not plug one extension cord into another." By doing so, one directly violates this instruction, and this fact has been proven on many OSHA inspections, resulting in direct citations. No one is questioning an electrician's or engineer's ability to not overload a cord, but that is simply not all of the picture.

Jimbo - 18 February 2019 Reply

Ok I have a brinks timer with one single plug can I use an extension with this to power 2 lights ? Tungsten says 1250 w thanks .

Claudette Katerere - 18 February 2019 Reply

Are there permanent extension cords that can be used long term? I live in an apartment unit and landlord won't install more plugs, so I need something that I can permanently use for my TV radio etc, because the two wall sockets close enough are already being used for the cable box and home phone.

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