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Thread: Extension cord for 240v

  1. #1
    Join Date
    Jun 2016
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    Extension cord for 240v

    There was a related post and Jim B gave a good answer about extension cords, but wanted to ask a case-specific question.

    I have a 240v jointer and just bought a 240v dust collector. Both 20 amps. I had a sub panel with 240v outlets installed but still need to use an extension cord for both.

    Is a borg 12 gauge, 9í oven extension cord (that is about 5í too long for each machine) acceptable, or should I get one of the thick rubber bulk cords and build a shorter diy cord with the appropriate connectors?

    If the latter, what gauge, and should they hang between the outlet and the machine so the donít touch the concrete?

  2. #2
    Quote Originally Posted by Todd Zucker View Post
    There was a related post and Jim B gave a good answer about extension cords, but wanted to ask a case-specific question.

    I have a 240v jointer and just bought a 240v dust collector. Both 20 amps. I had a sub panel with 240v outlets installed but still need to use an extension cord for both.

    Is a borg 12 gauge, 9’ oven extension cord (that is about 5’ too long for each machine) acceptable, or should I get one of the thick rubber bulk cords and build a shorter diy cord with the appropriate connectors?

    If the latter, what gauge, and should they hang between the outlet and the machine so the don’t touch the concrete?
    I would go the Black SJO cord route, with correct plugs. This way, you can make them the exact needed length. As for gauge, I would use 12 gauge, unless they are more than 25' long.. Second option would to be to use "oven cord," cut it to correct length, and add needed connectors. I would let it lay on the floor to avoid a tripping hazard.

  3. #3
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    Before I got an additional breaker box installed in my garage, I had to run a couple of 240V machines from an outlet on the opposite side of my 30'x30' garage.

    So I bought this 240v 20A extension cord from Amazon. By the time I would have bought the cable and two connectors, I probably would have saved about $10 tops versus buying the extension cord.

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

  4. #4
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    Get a good 12 ga 120 V extension cord (usually 50' or 100', as short cords are typically lighter weight), remove the molded ends, and add quality (e.g., Hubbel, etc.) 240 V ends.

    Buying cord by the foot is expensive, as is buying ready-made 240 V cords.

    If you cut your length from the middle of a long cord, you can make two nice 25' or 50' 120 V cords from the remaining ends with one of the molded ends each.

    Color the ends of the white wire black or red with a marker or tape, so it isn't mistaken for a "common" conductor.

  5. #5
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    The oven cord will work fine if it has the correct terminations. I don't like those kinds of cords, however. My preference is to make them up with the rubber coated bulk cord material in the appropriate gage/wire count because it's more durable, IMHO, but as you note, I recently used a couple of 12 gage exterior extension cords from the 'borg that I reterminated with twist locks which is my shop standard in my temporary shop to get power to a couple of machines. (those cords are not exposed to foot traffic as things are setup) Both of those machines only require 20 amp circuits. Actually, the PSC appears to only require 15 amp given the factory plug is a 15 amp blade-type 240v connector, but my circuits can handle up to 30 amps.

    One thing...ideally, any extension you use should only be long enough to do the job while not posing a safety issue with how it routes to the receptacle. That's an advantage of making up your own regardless of your cord material source.( I happen to like having only pigtails on the actual machines, too, but that's a different conversation)
    --

    The most expensive tool is the one you buy "cheaply" and often...

  6. #6
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    Mar 2003
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    Upland CA
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    I have made a couple. My solution was to buy a two pack of 12GA-50' extension cords at Costco, cut the ends off and put 240V connectors on the ends. If you want 25' make two out of one of the cords and keep the other.
    Rick Potter

    DIY journeyman,
    FWW wannabe.
    AKA Village Idiot.

  7. #7
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    West Lafayette, IN
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    This is why I pickup SO cord when I come across it and a garage sale or auction. It is pricey and makes excellent machine cord. Most of the time I find 4 wore that was used for 3 phase, but I just clip one wore short and abandon it. I know technically this is not good practice but I am a one-man hobby shop and and it is not permanently installed or anything.

  8. #8
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    Lake Gaston, Henrico, NC
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    I'm still using SO cords that I put together in the mid 1970's. I've replaced some ends, but not that many. SJ will not last nearly as long. The important letters are the first two -S, and O. There will be all sorts of combinations behind those that mean something each, but those aren't that important for a woodworking shop. If SOOW is all you can find, that is just fine.

    I find that dedicated electrical supply stores, if your state is one that allows people off the street to buy from them, to be no more than half what the box stores get for it.

  9. #9
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    Cambridge Vermont
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    I make my own cords to the length I want. SOOW has a thicker rubber jacket and is rated for 600v while SJOOW has a thinner rubber jacket and is only good to 300v. I don't care for extension cords that are too long. Also Avoid using cable for an oven as the jacket isn't going to provide the same protection as SOOW from something accidentally falling on it. One of the last thing I would want to witness in my shop is 20 amps shorting across both legs of a 240v line.

  10. #10
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    Houston
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    The responses remind me that I still have a lot I need to learn about shop safety as the machines in my garage get bigger and more numerous.

  11. #11
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    Quote Originally Posted by Todd Zucker View Post
    The responses remind me that I still have a lot I need to learn about shop safety as the machines in my garage get bigger and more numerous.

    True for all of us; both for new information and refreshing what we've already learned, but, um...mentally neglected.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  12. #12
    Join Date
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    E TN, near Knoxville
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    I buy heavy duty flexible cord and quality connectors from an electrical supply house to get the exact length and wire gage I need. To size the wire calculate the voltage drop based on the total distance from the panel to the machine including the wire in the wall. Using a larger wire size than required doesnít hurt.

    The last 240v extension cord I made is 25í long and carries 50 amps to feed welders and plasma cutter when working on projects and equipment outside the shop. I canít remember the gage but the cable diameter is huge.

    JKJ


    Quote Originally Posted by Todd Zucker View Post
    There was a related post and Jim B gave a good answer about extension cords, but wanted to ask a case-specific question.

    I have a 240v jointer and just bought a 240v dust collector. Both 20 amps. I had a sub panel with 240v outlets installed but still need to use an extension cord for both.

    Is a borg 12 gauge, 9í oven extension cord (that is about 5í too long for each machine) acceptable, or should I get one of the thick rubber bulk cords and build a shorter diy cord with the appropriate connectors?

    If the latter, what gauge, and should they hang between the outlet and the machine so the donít touch the concrete?

  13. #13
    Yes, there's a lot of reading to be done on this to understand voltage, current, and power. It's not completely intuitive.

    Your 240 power cord in fact transmits the same power by raising the voltage. This allows the amps to decrease. It's amps that are at risk of burning a cord, blowing a breaker, and causing loss over long distances. So, in fact, your gauge constraints on the extension cord would be less on a 240v extension cord than a 120v extension cord - for a machine drawing the same power.

    You should size your breaker to the amp draw of your tool, and your cord to the max amp allowed through that breaker. You may know all this...

    I will say that I bought this cord for my jointer/planer and bandsaw:

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    It is 12 gauge. It works fine for my loads. I've made my own cords, but the ends always end up pulling away from the cord over time. YMMV.

  14. #14
    Join Date
    Feb 2021
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    Western North Carolina, USA
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    Hi Todd,

    You may want to take a look at a simple online voltage drop calculator.
    Here's one, of many:
    http://wiresizecalculator.net/calcul...oltagedrop.htm
    I would go for no more than 1% voltage drop.
    (5% V drop or even more can usually work for a temporary situation.)
    Fancier calculators take into consideration heat from a bunch of wires stuffed in
    an underground conduit, ambient temperature, insulation temperature rating and more.

    For 20A circuits, 12ga is the common minimum gauge, regardless of length.
    For your short lengths 12ga is plenty adequate.

    Thanks and good health, Weogo

  15. #15
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    Mar 2003
    Location
    Vermont
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    All of my 240V machines run from extension cords at the moment. I used 12-ga SJOOW bulk cord and Hubbell connectors. Been working fine for years. I try not to step on my cords but it doesn't seem to hurt them if I do.
    Jon Endres
    Killing Trees Since 1983

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