Extension cord question

[Robert Todd]

Will using too light duty of an extension damage or destroy a motor?

[Dave Zellers]

Of course!

[Mike Henderson]

A too light extension cord will have a lot of voltage drop between where you plug it in and where the motor is. That means you'll be running the motor at too low a voltage. When you run a motor at too low a voltage, it will draw excess current. The excess current through the motor will generate excess heat and that can destroy your motor.

Mike

[Dave Beauchesne]

A too light extension cord will have a lot of voltage drop between where you plug it in and where the motor is. That means you'll be running the motor at too low a voltage. When you run a motor at too low a voltage, it will draw excess current. The excess current through the motor will generate excess heat and that can destroy your motor. Mike

Well said Mike!!

[Earl McLain]

It could be destructive to the motor in two ways--the one already mentioned (involving only the motor)--or--it could damage the motor in the fire that starts from the cord itself becoming overheated. I worked late last night, and saw the cord we supplied to our cleaning lady for the vacuum cleaner. I bet the plug was close to 100 f. I bought a 16 gauge cord on the way to the office this morning--would be embarrassing for an insurance office to burn due to too light of an extension cord!!

earl

[Robert Todd]

Thanks all. I knew you should always use a cord rated for the motor but I wasn't sure if an inadequate cord would harm the motor or just reduce performance.

[Steve Peterson]

There is often a small table buried in the 5 pages of warnings in the owners manual that lists the proper wire gauge depending on length and motor size.

Steve

[Keith Hankins]

yep bad news and could burn your house down. I've had to use them from time to time in the past and depending on distance from your main, it can be a real issue. I made the best one I had. Submerseable pump wire works great with the appropriate plug on the ends. If you do 20A use 12AWG min. If you use 30A, 10AWG. There are some good factory ones for sale but are pricey. They are found in generator supplies sections. I've got a good one made up so when power fails I can get power to the house. Take care and happy turkey day.

[Mike Henderson]

It could be destructive to the motor in two ways--the one already mentioned (involving only the motor)--or--it could damage the motor in the fire that starts from the cord itself becoming overheated. I worked late last night, and saw the cord we supplied to our cleaning lady for the vacuum cleaner. I bet the plug was close to 100 f. I bought a 16 gauge cord on the way to the office this morning--would be embarrassing for an insurance office to burn due to too light of an extension cord!!

earl
Unless you know that 16 gauge is sufficient and a 14 gauge is too bulky, I'd buy a 14 gauge. It's not that much more expensive and you will be able to use it for other things.

Mike

[Von Bickley]

Unless you know that 16 gauge is sufficient and a 14 gauge is too bulky, I'd buy a 14 gauge. It's not that much more expensive and you will be able to use it for other things.

Mike

I agree with Mike

I never buy 16 gauge cords.

Another thing to consider is when you are buying extension cords, if you need a 100 ft. cord, get two 50 ft. cords. Then when you need a shorter cord, you don't have to deal with a long one.

[fRED mCnEILL]

A number of years ago my son was living in my motorhome for a few weeks in the winter. We ran a 100 ft cheap extension cord from the house for an electric heater. One night it was especially cold (10-15 deg) and there was snow on the ground. My son said he aslmost froze and when we looked at the cord there was a line of melted snow when the cord ran. All the power had been used up in the cord with LITTLE left for the heater. Bought a 12 ga cord and it worked perfectly.

[Wade Lippman]

FWIW Harbor Freight has good prices on extension cords. That and nitrile gloves are about the only things I buy there.

[David Helm]

In all my years as a carpenter/builder I never allowed anything but 10 gauge extension cords on the jobsite. Many of the cords were 100 footers so anything smaller would have been damaging to tools due to the voltage drop.

[Myk Rian]

It could be destructive to the motor in two ways--the one already mentioned (involving only the motor)--or--it could damage the motor in the fire that starts from the cord itself becoming overheated. I worked late last night, and saw the cord we supplied to our cleaning lady for the vacuum cleaner. I bet the plug was close to 100 f. I bought a 16 gauge cord on the way to the office this morning--would be embarrassing for an insurance office to burn due to too light of an extension cord!!

earl
16 gauge is lamp cord. Get a 12 or 14 gauge. That 16 will do the same thing the other one did.

[Earl McLain]

My error, it was a 14ga cord, 16' long. The few I have in my shop are 12 ga, as short as functional--though I do have a pair of 10 ga that are 50' each for when I have to get outside.
earl

[Rick Christopherson]

Just to set the record straight on a couple of things. First, voltage drop does not damage a universal motor (such as a drill). It will cause the drill to run slower, which is the same method most drills use to control their variable speed.

Secondly, a long extension cord (of proper size) in itself does not pose a fire hazard. The cord will not heat up any more that it would if it were shorter. The wire gauge and amperage determines whether the cord overheats. (A coiled cord is different, and even a properly sized cord can overheat because the heat cannot escape the inner coils.)

Thirdly, the majority of voltage drop occurs at the plug, not the cord. So using two 50-foot cords will result in more voltage drop than a single 100-foot cord.

[Chris Friesen]

Thirdly, the majority of voltage drop occurs at the plug, not the cord. So using two 50-foot cords will result in more voltage drop than a single 100-foot cord.

Got a reference for this? A plug/receptacle connection in good shape is direct metal to metal contact, and should cause minimal voltage drop. The voltage drop in the cord is due to Ohm's law and is simply related to the size of the conductors and the length of the cord.

[Rick Christopherson]

Got a reference for this? A plug/receptacle connection in good shape is direct metal to metal contact, and should cause minimal voltage drop. The voltage drop in the cord is due to Ohm's law and is simply related to the size of the conductors and the length of the cord.Yeah, "Me". I designed and fabricated the equipment to test them. The tester in the picture below is intended to run several diagnostic checks, including load-banking, on power cords ranging from simple 15-amp, 120V, on up to 100-amp, 3-phase wye.

The cord-and-plug connection is a simple sliding compression fitting. It therefore does not have a very large surface area of contact, nor a very low resistance (relatively speaking) connection, due to the light compression of the fitting.

All voltage drop is related to Ohm's Law. It doesn't apply to just the length of a piece of wire.

http://www.rts-engineering.com/tempgraphics/PDT-R5-lo.jpg

[Dave Zellers]

Awesome. A real life movie scene!

[Rob Feldner]

This seemed like a good page to take a look at:
http://www.mikesenese.com/DOIT/2011/04/whats-the-right-extension-cord-length-for-my-tools/

Especially the pictures at the bottom. I've had bad cords melt on me, and all of them burnt up at one of the plug ends. Those pictures should make anyone think twice about using a questionable or overloaded cord, especially if it is left unattended.

[Mike Cutler]

Yeah, "Me". I designed and fabricated the equipment to test them. The tester in the picture below is intended to run several diagnostic checks, including load-banking, on power cords ranging from simple 15-amp, 120V, on up to 100-amp, 3-phase wye.

The cord-and-plug connection is a simple sliding compression fitting. It therefore does not have a very large surface area of contact, nor a very low resistance (relatively speaking) connection, due to the light compression of the fitting.

All voltage drop is related to Ohm's Law. It doesn't apply to just the length of a piece of wire.

http://www.rts-engineering.com/tempgraphics/PDT-R5-lo.jpg

Rick

Now that is a nice machine. I want one!

To back you up a little;
A few years back I had to prepare a class/lecture on extension cord use in an industrial environment. I happened at the time to actually get on the phone with the person responsible for testing and certifying extension cords at UL, Underwriters laboratory. At that time, he stated that no testing had been performed at UL to certify one extension cord being plugged into another, specifically for the reason you mentioned, heat at the mechanical connection of the two cords.
If you own the patents on that test box, and sell them, please PM me. The fallout from my class was good in that anything smaller than 12AWG is banned on site, but we are no longer able to make our own extension cords, or repair them, because we cannot certify them.

A 100' 10 AWG extension cord is about $120- $140.00, so unless folks can buy "SO" cord in 1000' rolls, it will be hard to make a cord cheaper than you can buy it.

[Rick Christopherson]

Rick

Now that is a nice machine. I want one!

If you own the patents on that test box, and sell them, please PM me. Thanks. I never bothered to patent it because the brains are in the software, and I have that locked out with a password in both of the processors it takes to run it. I haven't built one in years because each unit is custom designed for each client, and I got tired of creating new code for each model. The one shown was specific for a cable manufacturer, so it has all of the bells and whistles.

After building the first one nearly 2 decades ago, I got into the habit of photographing ever square inch of the internal wiring just in case one of them ever needed service. That paid off when one of them had a forklift driven through the LCD display and I had to walk a technician through the process of replacing it with a new one that I pre-programmed specifically for their model.

Lest anyone thinks it is just putting some plugs on the outside, here is a picture of the inside of that particular model. The program is so complex that I got the PLC to do things that the original design engineers didn't know their PLC was even capable of doing. (That was an entertaining email exchange, let me tell you. :D). To keep it sort of woodworking-related, I used to build my own enclosures in the woodshop, until I discovered it was more efficient to hire it out to a specialty shop. But in the mean time, I got pretty good at welding plastic.

Oh, not to burst your bubble, but this unit was $8000 several years ago.

275920

[Chris Friesen]

Yeah, "Me". I designed and fabricated the equipment to test them. The tester in the picture below is intended to run several diagnostic checks, including load-banking, on power cords ranging from simple 15-amp, 120V, on up to 100-amp, 3-phase wye.

The cord-and-plug connection is a simple sliding compression fitting. It therefore does not have a very large surface area of contact, nor a very low resistance (relatively speaking) connection, due to the light compression of the fitting.

That's a pretty sweet setup. I've considered building something similar to test A/V patch cables and ethernet cables. (I did Engineering Physics in university.)

Anyways, just for fun I just did a test. I had a 25" 12-gauge extension cord handy, and the female end is one that I put on so it was easy to take off to provide good measurement points.

Measuring the resistance of the individual conductors with a DMM gave 0.15 Ohms for each conductor, which is about as low as my little meter will reliably go. (For an ideal copper conductor of that size it should be about a quarter of that.)

I then plugged the cord into a contractor-grade receptacle I had laying around and measured the resistance of the cord+receptacle combination, and observed no measureable change.

So while I'm sure there was some change, it's below the level that a couple-hundred-dollar multimeter can measure. To do any better I'd need to pull out the lab-grade current supply but I'm too lazy to do that right now. :)

Now sure, if you take a crappy plug and stick it into a worn-out two-dollar extension cord, then you're going to have problems. But a contractor-grade plug into a contractor-grade receptacle seems to be a different story, at least in my simplistic test.

[Ole Anderson]

Probably like many others, I have cut extension cords to make two smaller cords. Did that for my RV using a 12 ga cord and a quality male plug on the cut end. I tinned the stripped conductors and inserted them in the clamp style screw clamps, not the type where you wrap the conductor around the screw. I use the cord to power the RV when it is in my drive at home. The RV has a power management panel and when you select 20 amp (vs 30 amp) is sheds loads to maintain no more than a 20 amp load. Running near 20 amps for an extended time severely overheated the male plug melting the plastic. When I took it apart, the overheating appeared to take place at the conductor/screw clamp interface, even though the screw was tight. I bought an exact replacement plug, this time skipped tinning the conductors. Ran the same loads again, this time the plug was barely warm. Go figure.

[Steve Milito]

275920

Nice clean work there.

[Rick Christopherson]

..... I tinned the stripped conductors and inserted them in the clamp style screw clamps, not the type where you wrap the conductor around the screw......... I bought an exact replacement plug, this time skipped tinning the conductors. Ran the same loads again, this time the plug was barely warm. Go figure.The reason is that when you tinned the end, you created a single, round conductor instead of a bunch of smaller ones. The surface area of contact was much lower than it would be when many strands of wire are in contact with the clamp.

[Phil Thien]

The reason is that when you tinned the end, you created a single, round conductor instead of a bunch of smaller ones. The surface area of contact was much lower than it would be when many strands of wire are in contact with the clamp.

I'll just add that many instructions for clamp-type connectors specifically instruct the user to NOT tin the wires. When you tin the wire the clamp cannot "smoosh" the strands to into the right shape to get maximum contact area. Also, solder is somewhat plastic even when set and over time a clamping connector that once seemed tight will loosen.

[Sal Kurban]

I would like to insert a question here (sorry if I am hijacking the thread :) I recently wired a rotary phase converter using a 60 amp circuit and 6 awg wire. But I used a 50 amp receptacle/plug and plugged the RPC cord (again 6 awg) into it instead of direct wiring. This way I can move the RPC around when not in use which sits on a cart (with rubber tires to absorb the vibration). Question is: does using a 50 amp receptacle/plug combo on 60 amp circuit degrade the power? Beyond 50 amps the receptacle/plugs are harder to find.
Thanks,
Sal.

[Chris Friesen]

I would like to insert a question here (sorry if I am hijacking the thread :) I recently wired a rotary phase converter using a 60 amp circuit and 6 awg wire. But I used a 50 amp receptacle/plug and plugged the RPC cord (again 6 awg) into it instead of direct wiring. This way I can move the RPC around when not in use which sits on a cart (with rubber tires to absorb the vibration). Question is: does using a 50 amp receptacle/plug combo on 60 amp circuit degrade the power? Beyond 50 amps the receptacle/plugs are harder to find.

The plug/receptacle you are using is rated for 50A. Using it for more than that for extended periods of time is a code violation and possibly unsafe.

(I specify "extended periods of time" because any plug/receptable is rated for brief amounts of overcurrent, as seen in motor inrush current for example.)