Electrical question

[Wayne Spence]

I recently noticed an ad for a table saw with 220 volt motor and 100 ft of extension cord. I am not interested in the saw but the idea of running an extension cord from my house to work shed would be an economical way(I think) of getting 220 power to the shop. Use would be for an air compressor. Other uses such as saws and lathe would be a possibility but not needed as I do not have 220 v motors and are not needed. An air compressor with 220 would be a great help to me as I use an air hammer and chisel frequently.

My question is 2fold. Is the voltage drop for 100' or less too much for 220 assuming 4 hours use a day - would it damage the motor? Is an extension cord that long within code for most communities in the US.

 

[James Seyfried]

I recently noticed an ad for a table saw with 220 volt motor and 100 ft of extension cord. I am not interested in the saw but the idea of running an extension cord from my house to work shed would be an economical way(I think) of getting 220 power to the shop. Use would be for an air compressor. Other uses such as saws and lathe would be a possibility but not needed as I do not have 220 v motors and are not needed. An air compressor with 220 would be a great help to me as I use an air hammer and chisel frequently.

My question is 2fold. Is the voltage drop for 100' or less too much for 220 assuming 4 hours use a day - would it damage the motor? Is an extension cord that long within code for most communities in the US.

There are a lot of variables involved in answering your question…more information is required. Such as, the size of wire, material, amps drawn, and even ambient temperature. This is the basic formula: Vdrop=IR. However, there are many voltage drop calculators available online. Here is one: Voltage drop calculator

 

[john lucas]

All of the above however if you have a compressor that's large enough to need a 220 motor it won't be running 4 hours a day I don't think. It should run for a pretty good while before needing to refill the tank. I'll let the electrical experts give you a better scoop on that end.
I'm looking at sort of the same problem. I don't use my compressor as much so I figure I can run it first thing in the morning and then switch it off so I can run the other 220 tools on that line. Then if I need it I'll shut the other tools down and turn the compressor back on for few minutes to refill. That way I won't have to run an additional line out to the shop.

 

[Wayne Spence]

Correct-The compressor will not run for 4 hours. My experience with 115 volt compressors is that you are operating right at the limit in both amps drawn and cfm. Air hammers for stone use 4 to 6 cfm, the larger 8 to 10. Die grinders are a lost cause.

Do you have any experience using air hammers and chisels on wood? The variety of chisels is limited but I can see a use in roughing out. All of my work with air hammers is on stone, a combo on stone and wood could sure make the equipment list smaller.

 

[Bill Boehme]

There are all sorts of extension cords, but the most important factor is the wire size (shown on the jacket of the wiring as AWG (American Wire Gauge) followed by a number. Extension cord sizes range from as small as 18 gauge for some of the very light duty cords that could be used with LED Christmas tree lights to 16 gauge (the most commonly used extension cord size) and heavier duty for a heavier duty price tag. AWG 16 would be OK for something like a drop light or drill or sabre saw, but definitely not a non-portable tool. Sometimes you can find heavier duty extension cords in AWG 14 and AWG 12. AWG 12 will work with most stationary power tools (but not all of them -- I made up 10 gauge extension cords for my Delta Unisaw and my Mini Max MM16 bandsaw). Using 240 VAC actually has an advantage when used with extension cords since the current would be half of what it would be if the motor were configured to run on 120 VAC.

Extension cord wire size is typically a little smaller in size than permanent wiring even though the gauge is the same. However, if you buy the heavy duty black rubber wire off the spool (type SOOJ or SJOOW) and then install heavy duty connectors, you will have a better heavier duty extension cord with the same wire cross section as your permanent wiring.

Wire length becomes important whether talking about permanent wiring or extension cords and it is necessary to derate the wiring over certain lengths. You can probably find information on that by Googling "derating extension cords".

 

[Fred Belknap]

Worked construction for years and we used some extreme extension cords sometimes. Sometimes we would plug 2 or 3 100' cords together and run saws and drills ect. It worked pretty well. We didn't really care much about damage to the tools as (get er done) took precedent over tools.

 

[billooms]

The biggest issue with an air compressor is the start-up current. When it first turns on, there is a big jolt of current to get the motor running against the back-pressure on the compressor. With a long extension cord you might get too much voltage drop on the start-up surge (especially if it's not big enough wire). Saws and other equipment also have a start-up surge, but not nearly as much as with an air compressor.

 

[Dean Center]

A length of UF wire in the right gauge might make a pretty good 'extension cord'.

 

[Dale Miner]

The biggest issue with an air compressor is the start-up current. When it first turns on, there is a big jolt of current to get the motor running against the back-pressure on the compressor. With a long extension cord you might get too much voltage drop on the start-up surge (especially if it's not big enough wire). Saws and other equipment also have a start-up surge, but not nearly as much as with an air compressor.

To add to what Bill pointed out;

If the voltage does drop too low, with a single phase motor, the motor will not reach enough rpm's to open the centrifugal switch on the starting windings. Those windings are not meant to be continuous duty, and will burn out in a short time.

I have about 300' of #10 buried feeding the barn. My 2hp 110 compressor will start fine in warm weather, but in cold weather the tank must be drained to nearly zero pressure for the compressor to get up to speed. Once running the motor will fill the tank normally and shut off, but won't come up to speed again without draining. This compressor has an unloader valve to dump the reciever pressure to allow for an easier start, but the pressure builds in the reciever and prevents the motor reaching speed when fighting the cold oil and back pressure.

The cost of a good heavy drop cord is substantial, but will last for decades if taken care of.

 

[Dennis J Gooding]

Some further relevant comments: When computing the voltage drop remember that the length of conductor is twice the reach of the extension cord. Furthermore, unless the outlet is at the service panel you will get additional voltage drop in the interior wiring of the house. In the example cited by Dale, his 300 ft of #10 cable would have a total conductor length of 600 ft and a resistance of 0.6 ohms (from standard wire resistance tables). A 50 amp starting current would produce a voltage drop of 30 volts in the extension cord plus additional drop in the house wiring.

Dennis

 

[Ken Burns]

Type your numbers into this calculator and find the correct wire size (your 100 ft. distance is half the actual circuit length):

http://www.csgnetwork.com/wiresizecalc.html.




Ken

 

[Wayne Spence]

Thank you one and all. Some good information as usual. After the first of the year I will run the line to the other end of the house and put in a receptacle for the extension cord. It is then 25 ft to the work ched. I may at a later date put the line to the shop without interruption, there is a lot of concrete to go under but the electrician says it is no problem. All the while he is working on the calculator with a smile on his face.