Introduction: The Extension Cord From Hell

Picture of The Extension Cord From Hell

How to build a hybrid extension cord/outlet strip.

DANGER: This project involves household outlet voltage. DO NOT ATTEMPT IF YOU ARE NOT FAMILIAR WITH 120V HOUSEHOLD WIRING.

When the project is completed you have an adaptable extension cord. I used 5 outlet boxes, you can use as many or as few as you want, just change the length of the cord and parts count accordingly.

Step 1: Required Tools

Picture of Required Tools

To build this cord you will need:

A set of wire cutters
A wire crimper
A wire stripper or knife (or both)
A small and large flat blade screw driver
Pliers (needle nose or regular) (not pictured)

To test this cord you will need:
A Digital Multi Meter (not pictured)
An Outlet Tester (not pictured)

Step 2: Required Materials

Picture of Required Materials

To build this you will need:

1x 25ft 14ga medium duty extension cord
10x duplex outlets (buy the contractor's pack)
10x entry cable clamps 3/8 inch (fits half inch hole)
5x metal electrical box
5x metal box cover
70x 16-14ga 4-6 stud spade lugs (buy the 100 pack)

Step 3: Box Prep

Picture of Box Prep

To prepare the box for use you will need to do the following:

1). Use a screwdriver to pop one of the small holes on the top and one on the bottom out.
2). Use the pliers to bend the small round cover until it breaks off.
3). Install the cable entry clamps into the holes. Orient them so the screws face sideways compared to the box (as seen in the pictures)
4). Build all of the boxes the same way.

Step 4: Wire Prep

Picture of Wire Prep

This will be the most boring and tedious section of the project. Do not skip the steps of crimping the spade lugs onto the cable! You will have a much easier time using the cable with the lugs on it. This also gives the cable a more professional build.

1). Identify how far from the plug to the first box (about 10 feet for me). Measure that length from the plug and cut the cable.

2). Strip about 6 inches of the outer insulation from the cut end of the cable. Be careful not to damage the inner conductors.

3). Strip about 3/8 inch of the insulation off of the black, white, and green wires.

4). Place a spade lug on the stripped wire and crimp it on.

5). Measure about 2 feet from the receptacle end of the cable and cut.

6). Strip about 6 inches of the outer insulation from the cut end of the cable. Be careful not to damage the inner conductors.

7). Strip about 3/8 inch of the insulation off of the black, white, and green wires.

8). Place a spade lug on the stripped wire and crimp it on.

9). Cut the remaining wire into 4 sections that are about 2 feet long and 5 sections that are about 6-8 inches long.

10). Strip about 6 inches of the outer insulation from each end of the 2 foot cable. Be careful not to damage the inner conductors.

11). Strip about 3/8 inch of the insulation off of the black, white, and green wires.

12). Place a spade lug on the stripped wire and crimp it on.

13). Strip all of the outer insulation off of the 6-8 inch sections (you want only the black, white, and green wires).

14). Strip about 3/8 inch of the insulation from each end of the 15 short wires, then crimp a spade lug onto each end.

Step 5: Outlet Prep

Picture of Outlet Prep

Prepare the outlets for installation into the box

1). Remove the screws from the tabs.

2). Depending on the box that you choose, remove the mounting ears.

3). Attach a black and white wire to each outlet in pairs. Attach the black wire to the gold screw, and the white to the silver screw. Do not use the green screw yet. I attach the wires to the bottom screws on the first outlet and the top screws on the second outlet.

Step 6: First Box

Picture of First Box

This is the first box in the chain.

1). Take the cable with the plug end on it, and insert it through the "top" cable clamp on one of the boxes prepared earlier, then tighten the clamp evenly.

2). Insert a 2 foot jumper cable through the "bottom" cable clamp on the box, then tighten the clamp evenly.

3). Attach the black and white wires from the cables to a pair of outlets, one cable to each outlet.

4). Attach a green jumper with and the cable's green wire to the first outlet's green screw, then attach the same green jumper to the other outlet in the pair with the other cable's green wire.

5). Install the outlets onto the box cover using the hardware that came with the cover (mine came with screws and nuts).

6). Install the cover onto the box. NOTE: Depending on where and how you plan to mount the box, it might be worth not fully installing the cover at this time.

Step 7: Last Box

Picture of Last Box

Now we build the last box in the series. I then build the intermediate boxes.

1). Insert a 2 foot jumper wire through the "top" cable clamp of the box, then tighten the clamp evenly.

2). Insert the receptacle end of the cable through the "bottom" cable clamp of the box, then tighten the clamp evenly.

3). Attach the cables to the outlets as you did for the previous box, including the ground wires.

4). Install the outlets on the box cover.

5). Install the box cover onto the box. NOTE: depending on where and how you plan to mount the box, it might be worth not fully installing the box cover yet.

Step 8: Intermediate Boxes

Picture of Intermediate Boxes

Now we assemble the intermediate boxes. These are very much like the first and last box, but you only use the jumper cables between the boxes.

Step 9: Checkout and Finished Project

Picture of Checkout and Finished Project

Before you plug this into the wall, some basic safety checks.

You need a Digital Multi Meter (you do know how to use one, right?)

Using the OHMS settings, check for shorts between the conductors on the cable. Neutral to ground, neutral to hot, and hot to ground. If you find any, check all your work and repair the problem. Check that the metal boxes are connected ONLY to the ground conductor! YOUR SAFETY DEPENDS ON THIS CHECK!

If the unit passes the short check finish installing the unit where you want it, make sure all the covers are fully tightened down.

Plug the unit into power. If you pop the breaker you plugged into, check your work for shorts again.

Use an outlet tester to check all the outlets, including the cable receptacle. If the outlet tester shows correct wiring in all the outlets, you can use the project. If not, find the error and repair it before use.


muttyfutty (author)2009-10-13

Nice, but isnt this a bit of, erm... Overkill?

capernius (author)muttyfutty2016-01-28

In most cases in my experience, 8 outlets on one line are enough...

however, if someone is in a band, 8 outs would only cover one person, or maybe 2 at most.

so it all boils down to what you want this for, and how many items will you have plugged in at one time...

Before you make something like this, draw up a list and/or a plan of what you need, what you want, and then go from there.

But for safety sake, ALWAYS have a GFI outlet first. It just might save your life.

kill-a-watt (author)muttyfutty2010-11-05

better to overkill then to have to bother to kill it over again.

theewz (author)2010-08-01

Could I use standard house wiring then add a three prong extension cord end? The wire is on sale here for 2$ a meter.

capernius (author)theewz2016-01-28

the safest way to make a cord like this is to have a GFCI as the first outlet & then have everything wired so if the GFCI pops, the whole line(outlets on the cord) shut down.

In America, the standard wire for homes is 14 gauge solid....

personally, I would rather use 12 gauge solid or strand. the heavier wire increases safety.

What kind or what gauge of wire is used, or is the standard outside of America, I have no idea, so I can not even guess as to what you should or could use.

elco_chan (author)theewz2011-05-31

You could it will just be less flexible.

justible (author)2009-01-04

Even if you had large guage wire, the breaker for the outlet you plug into is likely not rated for the kind of pull an outlet mess like this *could* attempt.

And the *wiring in the wall* between the outlet and the breaker would *also* not be rated for the enormous pull of a cord like this. This thing will start a fire for someone, somewhere.

THE_GEEK2007 (author)justible2010-08-22

Outlets do not pull any amps when they are not being used. Even if all of these were plugged into the wall, but nothing was plugged into them, there would be absolutely no usage at all. Also, the wiring between most outlets in your home is probably 14 gauge wire, just like the extension cord this person used.

ludionis (author)THE_GEEK20072011-02-15

The concern is that standard 14 gauge wire is rated for 15 amps. If you have this many sockets, generally, you're going to be using some/most/all of them, possibly exceeding the 15 amp rating. Also, bear in mind MOST outlets are not on isolated circuits, generally all the outlets from a room or several rooms are tied together, facilitating to potential overload.

General use extension cords are 16 gauge stranded wire, which will support even less. More likely a tripped circuit breaker before a fire, but fire is always a possibilty, especially with the on/off switch.

THE_GEEK2007 (author)ludionis2011-02-15

Even if it exceeds the 15 amp rating, it would just trip the breaker anyways.

capernius (author)THE_GEEK20072016-01-28

that is why it is ALWAYS a good idea to have a GFI on a home made extension cord

Nagarok (author)THE_GEEK20072012-03-18

Don't have such faith in things, The breaker may not be tripped until after the wire catches fire.

They only trip after a particular critical mass, and if your wire happens to fall in the zone where the household circuit is fine, but it's not. *shrugs*

This isn't a very safe instructible, there's a reason why extension cords are limited to the number that you'll find on power boards.

ccronkhite (author)Nagarok2015-03-29

It's only as dangerous as a person's use of it. You can just as easily daisy chain two or three surge protectors. If you have several tools being used at the same time then yes, this cord could be dangerous. I wouldn't use it at a job site or shop where several people would be working at the same time.

tyrantwing (author)THE_GEEK20072014-09-02

the average household does use AWG 14, however that is solid. stranded as are in cords would be AWG 12 to equal the same electrical flow as AWG 14 solid.

kessiambre (author)tyrantwing2015-09-12

actually, you get a higher current rating with stranded. it's kind of weird but I'm an apprentice electrician and it has the table in my expensive code book for all the wire ratings. Just sayin'. I'd probably do it all different tho!

capernius (author)2016-01-28

I noticed you did not use a GFI with this...

Is there a reason why?

I like this idea BUT, I would have used a GFI as the 1st outlet...that way if there is an overload, the GFI will pop before anything gets overheated in the wall or gets short circuited.

And the female on the end? personally I think it is a bad idea. kind of like an accident waiting for a place to happen. but generally speaking, this is a good idea.

espdp2 (author)2014-12-22

This is great, despite the naysayers. I move a lot, so my shop has to be SEMI-mobile. I may have 15 things plugged in, but I'm only using one or two at a time. Well, an LED task light, a small stereo, a cell phone charger, and a corded tool. That's all I can juggle at one time. All of the other tools are turned off, waiting to be used.


EvilMarker (author)2011-02-16

That is crkt m16 do I get a prize?

JamesHolden (author)2008-10-05

i would strongly consider adding a circuit breaker at the end that plugs into the wall. it would save you from costly problems down the road. i would also use plastic box's, if a wire came undone it would be a bit safer. and ofcourse, always make sure that cord is the only thing plugged into the circuit you're using. or atleast the only thing with high load devices on it (anything larger than a 100w bulb)

ranger_steve (author)JamesHolden2011-01-15

about the plastic boxes... i dont know about his plugs but the majority of plugs i have used in projects in the last 4 or 5 years have had the ground screw/terminal on the plug attached to the tab that the screw goes through to hold the plug to the box, so the box automatically becomes grounded as soon as the plug is installed. Or if the ground is hooked to the box then the ground
hole(s) on the plug become grounded.

ranger_steve (author)2011-01-15

here's some pics of my version...

ranger_steve (author)2011-01-10

nice ible! i plan on making a cord like this for my band, only with a 12/3 extension cord that i bought at costco wholesale yesterday. 100 feet for 45 bucks.

kill-a-watt (author)2010-11-05


A few points:

I found plenty of used outlets (mostly painted over) at the local Habitat for Humanity ReStore. They were 25 cents each.

The outlets could be free if you were changing out previously panted over outlets.

(I really hate it when people paint over outlets. Remove the cover, and mask with blue tape, people!)

By code, you need to also attach the ground to the boxes, then connect all the grounds together with a wire nut.

You can skip grounding the box if you instead use "special outlets" for this purpose, or switch to plastic handy-boxes. If you go plastic, please use plastic covers too.

If you have scrap armored cable or scrap conduit, you could use that between the boxes. At one point when the economy was good, you could find this in dumpsters all the time. Later, as copper went up, they took out the scrap copper wire, later than that they also kept the alumum sheathing to recycle. you can still find plenty of steel boxes, steel wall studs and sometimes outlets and switches too.

Something like this mounted to the underside of a desk would be great. I have something like this under the shelf in my garage.

wsanriv (author)2010-09-20

the 2 plugs are fine if you have all you wall sockets polarized, other wise a bad connection will leave a very dangerous short circuit.

g.laughlin (author)2009-01-25

extension cord from 7734 wow, I have one like that from the orange box store not as many outlets but there are little green LEDs in the outlets, for plugging in the dark. creating major envy on many a job site.
Junior electrical engineer's your 10 outlets per circuit rule is falsely based on NEC 220.14(I) this is only for calculating the total load of a building (any type) and has nothing to do with how many outlets can put on a circuit,that has every thing to do with the building wiring and the circuit over-current device.
And the GFCI every thing attitude. If you check the NEC 210.8 only in places where the user or equipment may come in contact with WATER, Bathrooms, Kitchens, Rooftops or Outdoors is GFCI protection required. so for all DJ types NEC 640.10(A&B) if your audio equipment is with in 5' of water you need GFCI protection, IT geeks, the last thing u want is a GFCI(power loss = Information loss), but you need to be Properly GROUNDED NEC 645.15

and never let a fool play with your tool

So you're saying I can't run this between my tub and toilet to power my 7.1 Dolby surround shower system? Awww, man.

gmjhowe (author)2008-09-08

Would you not be best using a 'cheat' It wires up so that you plug into two outlets at the sametime, allowing a better daisy chain. We used one alot when doing gigs.

0.775volts (author)gmjhowe2008-09-10

so that it can plug into two outlets? you mean ,like two male plugs on the end? that is absurdly dangerous. if you need that much power, you need more than one pit quad, and probably on seperate circuits.

gmjhowe (author)0.775volts2008-09-10

Thats right, we used it to run loads of equipment off when doing gigs, eg mixing desk amps, large speakers. It actually very safe, and safer than trying to run off one outlet. Normally the cheat is the only main thing plugged into the power in the building.

0.775volts (author)gmjhowe2008-09-10

yeah, that's really, really unsafe. first off, you have a live male plug, which is something that should never happen. up until now you you've been lucky, and haven't crossed legs by trying to use such a piece of equipment, which would either give you 240 v down the line, or just shunt massively when you plug the second connector in. Like i said Using ANYTHING with two male plugs on it is extremely unsafe, and should not EVER be attempted. if you need more current, buy a second extension cord and read up about load balancing. why would you risk losing all of your equipment for the price of a decent extension cord? I just doesn't make sense,.

gmjhowe (author)0.775volts2008-09-11

hmm, you don't seem to be reading me right - This is a professional level piece of equipment. You right with the two live male plugs - you have to be very careful, and basically plug and unplug at exactly the same time. But other wise, its alot safer than your making out. The cheat method is alot safer for the equipment, and is used often for people doing gigs in environments without dedicated power sockets e.g. it came in very usefull when playing at derby cathedral. Any more info than that and im going to come undone, as thats the most i know about it, if you want any more info, i will get my friend (whom uses/owns it) to explain more!

0.775volts (author)gmjhowe2008-09-11

Yeah, ask your friend for info. if it's an actual product, I'd like to see photos and/or a product link. I could see something like this being used with a 30/30 jack or something like that to support more than one phase of power (ie two legs down a four conductor cable. I've used 30/30 breakouts in the other direction. the problem with using something like that is that you would have to know which phases were which and how you were connecting to them.

gmjhowe (author)0.775volts2008-09-11

yeah, you see, i didnt get a word of that, it didn't make one bit of sense! i will ask him next time, all i remember is it went into like a triangular box with power outlets on it...

0.775volts (author)gmjhowe2008-09-11

ahh. not to be nit pikcy or anything, and I can understand how the difference may not be apparent, but that clarifies things. the solution you suggested here is not the same one that you;ve used in the past. the one you proposed is potentially deadly, whereas you used something different, sounds like a costom made distro or something,.

gmjhowe (author)0.775volts2008-09-11

yes something like that, there actually going to use it at a gig tomoro!

0.775volts (author)2008-09-10

we usually build out our pit quads (that's what this is) with 10/3 sjoow. even if you're just powering stand lights, it still adds up. I would recommend plastic boxes if you can find them, but use what you've got, I've seen more metal pit quads than plastic ones. also, if you want to adapt this for pit/backline use, three feet between boxes is pretty nice(though if you move it around alot it doesn't really matter what the span is)

sdallesasse (author)2008-09-07

It would be a good idea to put a GFCI as the first outlet and feed the rest off of the load side. This would allow you to place it anywhere without the danger of a shock due to water. Also I would use # 10 AWG for the cord. #14 only allows 15 amps, #12 20 and #10 30. This would give you a large buffer in case of overload.

defiant1 (author)2008-09-07

Wow, definitely check the wattage on EVERYTHING plugged in and do NOT exceed the limits of whatever gauge cord you use. I would also recommend a 15amp fuse inline somewhere if you don't have any fire insurance. Remember, It's easy to make electricity go in a circle, a little harder to do it right, and safely. This might work great for Christmas lights though.

guyfrom7up (author)2008-09-07

Hell caught on fire, they returned the extension cord to neosensi. They went to court and satin lost. He was too cheap to put out the fire.

joejoerowley (author)2008-09-07

Cool, but not the safest thing ever. I would do it still though.

Plasmana (author)2008-09-07

This is a good instructable! I might use this idea.. Thanks!

Kiteman (author)2008-09-07

Twenty appliances? Plugged into one wall-outlet? I'll probably be able to see the smoke from here...

Plasmana (author)Kiteman2008-09-07

Umm, no, 21!!!!!! Don't forget the end of the wire, there is a plug...

Hoopajoo (author)Kiteman2008-09-07

No kidding. My neighbor's house burned to the ground from an insufficient drop cord supplying a DVD player. With the amperage running through that cord, I bet it will burn you just to touch it. I would go with a 8 or 10 gauge cord and an inline breaker / GFCI as a minimal safety precaution.

TheWelfareWarrior (author)2008-09-07

not a bad instructable, the idea behind it is good too! as with what other people have said FIRE HAZARD... I wouldn't use powertools with it, maybe 1 or two but not anything bigger than a single skillsaw....

zuixro (author)2008-09-07

Wow, I was working on an 'ible just like this. Only I just put one box on an extension cord. At work we called them quad boxes. I liked them so much that I decided to build a couple for myself. I made mine pretty much the same way, only I didn't use spade connectors, I just made a hook of wire.

neosenshi (author)2008-09-07

Actually, this is built due to the need for multiple outlets in a 6 foot tall computer rack that will have mostly wall warts and 4 computers. Total Load in amps: about 8 amps. Rating for this unit as built: 15 amps. A commercial rack mountable power strip designed for this sort of use costs about $250. As for the use of the crimp on lugs: I work someplace that builds custom cables, and for stranded wire to a screw terminal, that makes the easiest connections. An electrician doesn't use crimp on lugs because they use solid wire, not stranded.

zachninme (author)neosenshi2008-09-07

I understand people's concerns, but I understand you know what you're doing. Still won't hurt to put a warning about the amps ;-)

ironsmiter (author)neosenshi2008-09-07

sadly, those metal boxes preclude my favorite safety device, for this sorta thing... a GFCI outlet. Just one, wired inline, protects the whole strip. I terminated my single box version of this, with a computer powersupply cord. It lets me plug in my pc, using the terminated PSU plug end. Monitor, Printer, external drive PSU, and cell phone charger plug into the 4 outlet receptacles. Very handy.

neosenshi (author)ironsmiter2008-09-07

Actually, they don't. I saw different covers that included cut outs for GFCI outlets.

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