Close electric cord call

[Wood_workur]

I only have 1 circuit in my garage, so I power my shopvac and some lights off another circuit, via a extension cord. Well, today when I was finished in the shop, I went to go umplug the cord, and coild it up, but when I went to pick it up, it was very, very hot, and smelled of burning electronice. I ran back into the shop to unlug it from the power strip in there, and to grab a fireextingusher. I kick the cord off my porch, and sprayed it with the fire exdtingusher. I unrolled the thing, and discovered that the plastic sheathing had melted, and the only thing tht kept if from shirting out was the paper surronding the wires. I again hosed the thing down with the fire extingusher, and the wheel that I wrap the cord around had melted in the middle. After some research, I came to the conclusion that the cord had reached about 300 degrees F, enought to melt the plastic, but not enough to set the paper on fire.

The lessons:

Don't gimp on extension cords. Buy the most heavy dity one you can find.

A fire extingusher should always be handy

Always unroll the cord off the reel before using it. Better yet, dont use a reel.

Always have a pair of heat resistant leather golves in you shop, for throughing hot stuff away from flamible stuff.

[bigstick509]

Good Point

Glad to hear everything came out OK. I finally got around to installing a fire extinguisher and carbon monoxide detector myself last weekend.

[niki]

Hi Alex
Nice experience you had there.
Rolling an extension cord, is almost the same like making electric heater (as you already know).

I would add to the “lessons”:
Check your machine Amperage and use one or two “Gauges” more than you need, refer to this table;
http://en.wikipedia.org/wiki/American_wire_gauge

Use the shortest extension cord that you can.

My TS is 11 Amp and I’m using 10 AWG extension cord that is for 30 Amp’s.

niki

[cabinetman]

In addition to the heat generated, I think I remember from a high school (yeah, they had high school then) science class that the coil of cord being electrified also creates a magnetic field in the center, or something like that.



"I'M NEVER WRONG - BUT I'M NOT ALWAYS RIGHT"

[Hellrazor]

Extension cords are evil. We have a few teachers at work who used to plug microwaves into those nice green ungrounded cords you use for christmas lights and such. Put an end to that quick, no ungrounded cords allowed.

[Stick]

The lessons:

Don't gimp on extension cords. Buy the most heavy dity one you can find.

A fire extingusher should always be handy

Always unroll the cord off the reel before using it. Better yet, dont use a reel.

Always have a pair of heat resistant leather golves in you shop, for throughing hot stuff away from flamible stuff.

All very true! My extension cords are all 10/3 or bigger (biggest is the extension cord for my welder, 50 feet of 6/3, that puppy is heavy!) and all have heavy duty ends on them. (I scored an entire 6' reel of salvaged 10/3 years ago for free, thousands of meters worth) I make them up in all different lengths, like 5', 10', 20', 25', 50', 100'. I have lots of each length, and they can be combined to make whatever length I need. They're stored on hangers marked as to their length, so it makes it simple to grab whichever lengths are needed. I also never leave them coiled up if they are plugged in, always lay them out straight.

I do the same with my arc welder cables, multiple shorter lengths to make up longer runs.

I use welding gloves for a lot of my day to day work, I have pairs all over the place. They're tougher than most work gloves, and thick enough to be pretty heat resistant.

Fire extinguishers.....a must for us all. I heat my house and all my shops with wood, of course woodworking involves dust, and I arc weld and O/A cut/weld which also involves lots of heat and sparks and grinding with its sparks, and do a lot of machining which involves cutting fluids etc so it's a triple need for me. I even have extinguishers on each tractor and in each truck. Had a fire once while haying, and was sure glad I had an extinguisher along!

[Wood_workur]

I'm going to the BORG tomarow, will pick ups some 10 gauge cords in a few legnths.

[scorrpio]

If the garage is attached, I'd rather run an extra circuit there. Might actually end up cheaper than a high-end extension cord.

[linear]

If the garage is attached, I'd rather run an extra circuit there. Might actually end up cheaper than a high-end extension cord.

And safer.

[LCHIEN]

technical comments

The reason why power wires get so hot in a coil has nothing to do with electromagnetic fields, it's simply because when coiled the heat is concentrated and there's no way to cool itself off. The wire is trying to give off heat to cool down, but is the wires next to it and on top of it are the same temperature, then the wire will get hotter instead of cooling.
Wires heat accordg to the power dissipated - a foot of # 16 gauge wire has .004 ohms. When running 15 amps in two conductors of an extenison cord, that 1-foot of cord is dissipating 1.8 watts. A fifty foot cord will dissipate 100 watts. Coiled up tightly it can reach light-bulb temperatures.
Stretched out, it will be pretty warm to the touch.

There are more dangers - the voltage drop will be pretty high at fifty feet - around 6 volts. so machinery operating at or near its rated power will try to draw considerbly more current to make the power.

So a coiled cord, long length and operated at high current will overheat, a double whammy because overheating raises the resistance of the cord, worsening things (resistance, temperature and voltage drop). The machinery will draw more current to compensate, in turn raising temperature, resistance and voltage drop.

Extension Cord ratings are for one-thing to ensure they don't overheat when laid out straight and allowed normal cooling. They do not compensate for voltage drop nor coiled up effects but they do allow for reasonably hot environments. If you are using the cords, for high current, do uncoil them so they can cool. If you are using them for lengths longer than about 10-15 feet, go up wire gauge step sizes (where a step is usually two gauge numbers, like 16 to 14 to 12 to 10 to 8 etc) for each doubling of length past 15 feet. This is to prevent the voltage drop from causing overload and therefore, over current problems.

I think I have seen 16 gauge cords rated at 15 Amps, that does not mean you can run 4 of them to go 50 feet with 15 amps, the voltage drop will be too high. I would go with two steps up, 12 gauge in a single 50-foot cord to handle 50 feet with 15 amps, at a minimum.

In the specific instance of the OP,
a shop vac draws maximum current when the vac hose is removed and the vac sucks the most air. 300 degrees is hot but believeable. Glad you weren't a story in the local newspaper - man injured when overloaded extension cord sets house/garage on fire.

[Russianwolf]

also note that constantly running a powertool on a long extension cord can reduce the life of the motor.

[onedash]

Is there any reason not to make an extension cord out of Romex? Other than the fact that its a lot stiffer wouldn't it beat most extension cords with an outlest and good plug???
My friends had home made extension cords in high school for their amps and lights and whatever else (band) and I know there were boxes with 2 or 4 outlets and I cant remember what kind of wire. They also had a big plywood box with switches to control their lights. pretty high speed huh?

[LarryG]

Is there any reason not to make an extension cord out of Romex?

I've done that, as a temporary measure. Works fine, apart from the stiffness issue you mention. Wouldn't be surprised to learn that there's some prohibition against it, say because the jacket isn't sufficiently durable or shouldn't be exposed to oils or whatever. And repeated flexing of the solid conductors wouldn't be good for them ... that's why extension cords use stranded wire. Still, it works, in a pinch.

[LCHIEN]

Is there any reason not to make an extension cord out of Romex? Other than the fact that its a lot stiffer wouldn't it beat most extension cords with an outlest and good plug???
My friends had home made extension cords in high school for their amps and lights and whatever else (band) and I know there were boxes with 2 or 4 outlets and I cant remember what kind of wire. They also had a big plywood box with switches to control their lights. pretty high speed huh?

Romex (type NM) would not make a good extension cord, one because its stiff (because it has solid and not stranded conductors) and repeated rolling and unrolling or folding would cause the wires to fracture and break. Second because the jacket is not designed for rough handling and wear that a extension cord would get. Third because there are not may fillers designed to spread the load should it be run over by vehicles or set upon by heavy objects. Fourth it is not moisture resistant - it has paper-like fillers.

There are heavy duty industrial jackets made for heavy duty cords, they'll be labeled, like SJO (oil resistant), SJ, and SJT (Thermoplastic for high temperatures), where they get a lot of wear and traffic. J is for Junior duty and is probably what you find on the typcail orange extension cables. These have heavy, oil and cut and moisture resistant jackets and better filllers to make them round and able to be driven over, repeatedly. Far superior to Romex and probably cost quite a bit more per foot, too, for comparable gauges. Also rated for different temperatures. Extra heavy duty S, ST and SO are for even heavier service.

Link to service types:
http://www.belden.com/pdfs/MasterCat...s/09_Portable%

Another useful article:
http://www.aces.edu/pubs/docs/Y/YANR-0055/

I have a number of extension cords of SJ or SJO cable where I put a double-wide conduit box on the end and two duplex outlets. You need a good conduit strain relief. I often attached a 6" long 2x6 piece of wood on the bottom as a weight to keep it upright.
You can also include a duplex switch/outlet combo and pilot light and circuit breaker is not a bad idea, you can get triple and even quad-wide conduit boxes in both plastic and metal.
But, nowadays, those outlet strips have all that and are much cheaper, especially if you are couting labor.