Is it safe to cut off the single-plug end of an extension cord and replace it with several regular receptacles and a metal box? Should the box itself be grounded?

  • good question because it falls outside of building codes or other sources of 'what's the correct way to do this'. might be better to reword your question from 'is it safe' to 'what are the safety issues' or 'how to do it safely'
    – mike
    Jul 16, 2013 at 1:32
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    That simply distils down to "How would OSHA do it?" Jul 16, 2013 at 1:54
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    +10 on OSHA, and my bad for not thinking of them. DIY extension cords must be pretty common in their jurisdiction.
    – mike
    Jul 16, 2013 at 2:12

3 Answers 3


I suppose it's safe as long as you wire it properly, including a secure attachment between the box and the cord to prevent the cord from pulling out. It certainly is not code-compliant, but temporary wiring like an extension cord isn't covered by electrical codes I believe. Yes, I would ground the box. (Depending on which outlet you install, it may be grounded automatically with the receptacle mounting screw, but I would do it with a pigtail anyway.

But why wouldn't you just use a power strip instead? Definitely easier and safer, probably similar in price to buying the parts individually.

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    Henry_Jackson - Thanks. It'd remind me of my dad, mainly. But power strips stiffen in the cold. Extension cords come with temperature ratings. And maybe I will attach a bracket on the back of the box to wrap up the cord for storage.
    – user14016
    Jul 16, 2013 at 0:45
  • You can always buy a long outdoor extension cord and then get a short power strip for the end, to give you extra outlets.
    – Hank
    Jul 16, 2013 at 1:54
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    @user14016 In addition to power strips (which include surge protection) you could use a simple splitter
    – BMitch
    Jul 16, 2013 at 2:29
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    The receptacle will not be "automatically" grounded, unless the box itself is grounded. And even then, it won't be grounded unless the receptacle is designed to ground through the yoke.
    – Tester101
    Jul 16, 2013 at 12:05
  • @Tester101: Guess my wording was unclear. Of course the receptacle itself should be grounded, I thought that was a given. I was saying the box may become grounded if the receptacle has a grounding screw / yoke, as you say.
    – Hank
    Jul 16, 2013 at 14:52

This would be considered to be temporary construction power equipment. According to OSHA rules (1910.305, 1926.405) there are specific requirements and the assembly is not for permanent use (running your hand saw for various jobs on the property vs running your freezer long term). Link to OSHA as they're not going away anytime soon: Acceptable Job-Made Extension Cords

The major focus is on using boxes meant for this type of use (boxes with no coined knockouts or that use screw-in knockout plugs), making sure all grounds are intact (including the metal box), neutral and hots properly routed so plugging the assembly in or items into the assembly will not reverse polarity and proper strain relief is supplied (no romex squishers) for the cord.

NOTE: While OSHA rules don't apply to DIY, the spirit of the rules is to increase your safety so Joe Electron doesn't escape through you!

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    +1. That link is interesting, although OSHA's rules probably don't apply for DIY home improvement, right? Also, what does it mean "All components must be approved for the purpose [...]", doesn't that basically mean you can't make a power cord from ad hoc materials?
    – Hank
    Jul 16, 2013 at 1:56
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    Well, you consult the OSHA rules for their recommendations, and per the rules, you can. Insofar as the safety environment it would create, while not under OSHA rules, DIY can use them as guidelines to work more safely. Jul 16, 2013 at 1:59

Is it safe? Maybe.

When you purchase an extension cord, that cord has been designed and tested to operate properly under certain circumstances. Once you modify the cord in any way, you've voided any listing or labeling on the cord (UL listing, etc.). If there is ever a fire, this could be a factor (but that's a legal issue, and outside the scope of the site).

If you know what you're doing, use properly sized cord, use the right box, and connect everything properly. Then yes, this can be done safely. However, if you don't know what you're doing, this can go horribly wrong.

It's not uncommon for homeowners and DIYers to be cheap. Because of this, they are likely to purchase lower end products. In the case of an extension cord, that means a smaller gauge wire (typically 16 AWG). In its unaltered state, this is almost never a problem.

Say you plug in your 12 Amp circular saw. Well the 16 AWG wire is rated at 18 amperes, and it's designed so only a single device can be connected at a time, so there is no problem.

Now lets say you've modified the cord, and attached a single duplex receptacle. you connect two devices, and draw a total of 20 amperes. Everything seems fine, since the receptacle will handle 20 amps, and the breaker back at the panel is also rated at 20 amps. The cord however, is only rated at 18 amperes. Now you start to smell something funny, and soon magic smoke begins to emit from the cord. Maybe you notice in time, maybe you don't.

You'll also want to consider the environment you'll be using the cord in. If you're planning to use the cord only in the shop, then a metal box might be fine. If you think you might ever use the cord outside, you might want to consider a weatherproof box and cover.

According to the manufacturer, modifying the cord in any way means the product is damaged and should be discarded. Modify extension cords at your own risk

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