Extension cords vs home wiring (noob question)

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slugboy6000

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Is there a risk when running long extension cords with high amp tools off of standard house wiring?
I use a 50 ft, 12 gauge extension cord with my 15 amp power tools, but often consider that homes are often wired with a smaller 14 gauge wire (?). I've seen plugs melt on extension cords which were too skimpy, could the same happen inside of a wall?
 
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John Gayewski

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14 gauge is for lighting only same for 15 amp circuits. At least around here that's the norm. I thought the NEC agreed, but I could be wrong.
 

jadnashua

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When running near max, it will generate at least a little heat. If the plug and socket aren't tight when you mate them up, replace as those will create heat which will reduce the tension which can create even more heat.

On a 20A circuit, the max continuous use should be 16A...on a 15A circuit, that would be 12A (80%).
 

Bannerman

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In Ontario, 14 gauge wire has been and continues to be most commonly utilized for lighting and general purpose circuits.

The correct circuit breaker/fuse to protect a circuit utilizing 14 gauge wire is 15 amps While a greater load than 15 amps will be usualy possible momentarially for starting a motor, the breaker/fuse will limit current draw to the maximum 15 amps. Connecting 12 gauge or larger wiring to a 15 amp breaker, will not result in higher current draw since the breaker is limiting the circuit to 15 amps.

Extension cords utilize stranded wire for flexibility, and with the additional insulation utilized for abrasion resistance, they don't dissipate heat as rapidly so the amp rating is often slightly lower than comparable solid conductor permanent wiring.

Your 12 gauge extension cord will reduce resistance through the extended wire length, which will assist to provide the entire 15 amps (1800 watts) possible to the tool that is connected.

If for instance you are using a table saw connected to a long length of 14 gauge extension cord, it is likely there will be sufficient resistance to cause the blade to slow while cutting a heavy piece of wood. Slowing the blade will result in higher current draw which will usually cause the breaker to trip. Using the less resistive extension cord will often allow the same saw fed from the same circuit to perform the same cut without overload. If using a 16 gauge cord, the saw may not even start while there is no load.

I've seen plugs melt on extension cords which were too skimpy, could the same happen inside of a wall?
Many extension cords utilize #16 or #18 wire, which are often used by people for operating devices beyond the capacity of that cord's wire and plug.
 
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jadnashua

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On a 50', 12g extension cord, from the wire only (not the plug and socket at each end), using 15A, you'd be supplying slightly over 1.2v less...over time, and if insulated, you might notice it getting warm. A 14g cord the same length would be losing about 50% more in voltage, about 1.8v A 16g one, would waste a bit over 3v. As you increase the resistance, you are creating a voltage divider, meaning that the supply voltage goes down at the end point, with a voltage drop over the wire from end-to-end. A small soldering iron you might use for electronics may only be a 10W device, and that can get to nearly 500-degrees F or so. That wouldn't work on soldering copper pipe, but works for much smaller leads to electrical components like on a chip. https://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table
 

wwhitney

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14 gauge is for lighting only same for 15 amp circuits. At least around here that's the norm. I thought the NEC agreed, but I could be wrong.
While that's a good practice, the NEC allows 15A receptacles on 15A circuits.

As to the OP, fundamentally, I see little difference between, say, a panel supply 25' of 14/2 NM, a 5-15 receptacle, 50' of 14 gauge extension cord, and a load, vs the same thing with 50' of 14/2 NM and 25' of 15 gauge extension cord. Of course, with 75' of 14/2 NM and no extension cord, you eliminate one cord/plug connection, so that may perform marginally better.

Cheers, Wayne
 

jadnashua

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The big differentiator is the quality and gauge of the plug/sockets, and the wire gauge. Every time you make a connection, it won't be perfect, and that will generate some heat, and your voltage will drop at the load. Do that enough, and you can run into problems. What might work today, might not tomorrow as the spring tension decreases. Plugging something into an old receptacle and the plug can almost fall out on its own. That's a problem! If the screws aren't torqued properly, and the current level is higher, the heating/cooling of things cycling can work the connections even looser, and worst case, you can literally melt the plug off the end of the cord and damage the receptacle...it also smells nasty!
 

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John Gayewski

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I remodeled a basement for my mother in law. Right exactly as I was moving some very minor electrical receptacles and lighting she started to get brown outs and would intermittently loose a leg of power on her house. I kept trying to explain how my work couldn't be the issue and I wasn't responsible for these events. She bitched and doubted me none the less.

After a few visits from the electricians they finally found the the utilities company had loose connections out in the transformer outside the house. Just from years of current running through the wires the connections were so loose it was like they had never been tightened. Tiny vibrations over years and years. I would have liked to smack my mother in law after this.
 
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jadnashua

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Do MIL's ever fully trust son-in-laws?

Electrical connections done with screws and screw-clamps should be tightened with the proper torquing tool. How often that happens, can't say. Heat does make almost everything expand. The connections aren't perfect, so they will have some slight resistance across them. Proper clamping force helps immensely, and there's enough tension for it to remain tight. The spring loaded connections used in a receptacle and some plugs is affected by the heat, too. The higher the current drawn, the more potential heat can be generated. Over time, and from repeated insertion/removals, that can loosen the connection and result in more heat, and sometimes, rapidly degenerating situations.

When I was in the Army, in one of our test stations, I happened to find the specs on one plug we used on our electrical meter. It was rated for ONE insertion...any time after that, the spring tension may no longer maintain specs, and the readings you might get from the attached probes might be suspect. Now, that was a real pain! Home plugs and receptacles are much more forgiving, but they can exhibit similar problems.

Bottom line, if the plug is easy to insert, it's time to replace the receptacle before you start to have real problems. Before I replaced all of them in my mother's house, if the cord was heavy, it might just fall out on its own if there was the slightest pull on it...not a good situation at all! I hadn't lived there for decades and only got there maybe once a year for a short visit, so didn't come across this earlier.
 
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