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How long can a power cord be?

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  • How long can a power cord be?

    Don't have "big" power in the garage but many homes have either a dryer, stove or A/C, I am not above running an "extension cord" out a window for a welder, how long can I make it before its just pointless or stupid heavy?

  • #2
    It's all about voltage drop.

    Problems are these:
    Connectors add voltage drop and can melt causing fire.
    Smaller gauge wire is worse than heavy gauge wire.
    Longer wire is worse than shorter wire.
    Higher current is worse than lower current.

    Extension cords are meant for hand drills, trouble lights, and radios.

    Things like welders, water heaters, and driers need to be wired properly to the distribution panel.

    My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."


    • #3
      I use a 25' extension cord for my welder ALL the time. In fact my TIG has been plugged into the extension cord for the last 10 years. I want to get some adapter plugs for it so I can run my stove and stuff from it as well.

      So long as you get a good size wire and good plugs there is no difference between running 100' of wire in the wall or 100' of extension cord on the ground.

      My 25' was over $100 by the time I got plugs and stuff.


      • #4
        As an alternate to the foregoing..... consider:

        What is the difference between an extension cord and "proper facility wiring"?


        Extension cords tend to be undersized for wire gauge

        Extension cords lay on the floor where they can be tripped over.

        End of story......

        if the extension cord is properly sized for the load, and some precautions against tripping over them are used, there is NO real safety difference.

        Furthermore, there is some relaxation of the "properly installed facility wiring" wire size allowed in the electrical code for welders, in consequence of the "duty cycle" they are used at (not 100% "on").

        An extension cord will likely be more expensive because it should be "SO" cord, meant for extra heavy service, with a jacket, padding, properly rated connectors, etc.

        The power got to your house on wires, it can get to your welder in wires also.

        Keep eye on ball.
        Hashim Khan


        • #5
          What MM says is true. BUT... cords are often used for welders and large loads. There are many voltage drop calculators on the Internet, or you can look at the NEC (National Electric Code) chapter 9, table 9 for conductor properties. You also will need table 310.15 to find the ampacity for a given wire size.

          First you need to know the current draw of whatever you are going to power from the cord. Then you need to size your cord accordingly (i.e. 30 amps= #10 wire). Then you can calculate the voltage drop of that wire size. 3% voltage drop is about the limit; then you will need the next size up conductors. I have copied a voltage drop example to follow from Mike Holt's web site. Just plug in your own numbers.

          240 volt Single-Phase Example: What is the operating voltage of a 44 ampere, 240 volt, single-phase load located 160 feet from the panelboard, if it is wired with No. 6 conductors, Figure 5?

          (a) 233.1 volts (b) 230.8 volts (c) 228.4 volts (d) 233.4 volts

          Answer: (a) 233.1 volts

          Voltage Drop = I x R

          “I” is equal to 44 amperes

          “R” is equal to 0.157 ohms (Chapter 9, Table 9: (.49 ohm/1,000 feet) x 320 feet

          Voltage Drop = 44 amperes x 0.157 ohms

          Voltage Drop = 6.9 volts, (6.9 volts/240 volts = 2.9% volts drop)

          Operating Voltage = 240 volts – 6.9 volts

          Operating Voltage = 233.1 volts


          • #6
            There's an oft forgotten problem with long extension leads.

            What do you do when you don't need a lead that long?

            Using one coiled up has been the cause of many fires.

            Sometimes just plugging in a coiled up lead, even with no load, is enough.
            Paul Compton


            • #7
              Originally posted by EVguru
              There's an oft forgotten problem with long extension leads.

              What do you do when you don't need a lead that long?

              Using one coiled up has been the cause of many fires.

              Sometimes just plugging in a coiled up lead, even with no load, is enough.

              Many say that is myth. However I never "wind/coil up" my cord when I'm not using the full length. I somewhat fold it up in a out of the way corner of the floor.

              I forget what size my cord is but I do know it is OVERSIZE for what the welder needs. When it comes to electrical cords I found that bigger is better than that one time "its not big enough".


              • #8
                I have a couple of #6 ga extension cords that I use for welders, etc. Never have had a problem with heat buildup in them either. They are about 30' long and work just fine.


                THINK HARDER




                • #9
                  1) My wife didn't want to fully unwind a 100' cord one day (only needed 10' or so). The next day I want to put it away for her - it was still plugged in. It was wound on one of those cord reels. It was definitely warm. I didn't believe it myself until that day.

                  2) I think insurance will come into play here too if something goes awry if it's plugged into an extension cord and shouldn't have been. Any reason not to pay out...



                  • #10
                    It's not a myth, you can run it coiled but the maximum load capacity is down-rated. Some shop bought reels (maybe all) have the down rating printed on them.

                    Also I have a 25 meters of extension cable with significant heat damage to prove it.

                    Not sure about the no load senario though. No load generating heat sounds like over-unit to me.


                    Originally posted by vpt
                    Many say that is myth.


                    • #11
                      I always use bigger than recomend. 10 ga is my smallerst also 4 6,8 ga. I use a 4 ga for 3 phase but it hard to handle as it's close to 11/4" in dia. But it works well until I get the big tools set in they're permanent place in the shop. Soon I hope.


                      • #12
                        Just stick a decent size piece of ferrous metal through the coil. Problem solved.


                        • #13

                          What is the current rating of your welder and how long do you want the cord to be?


                          • #14
                            Originally posted by philbur
                            Not sure about the no load senario though. No load generating heat sounds like over-unit to me.
                            It's because of the inductance. Energy is being stored and withdrawn. If there was no resistance in the cable, there would be no power being drawn and no heat.

                            If you've got one of those energy consumption meters that will display watts and VA, you can see the VA go way up as you coil the cable.
                            Paul Compton


                            • #15
                              I use a 100' 8ga cord for my Lincoln AC225 and have no troubles.
                              It might not get the swoopiest bestest welding at the high end, but
                              I don't do stuff that needs every last electron of welderizationing...

                              For the most part, it's used uncoiled --- because I need the distance.
                              The last 10-20' might be sort of coiled up somewhat, ish, kinda sorta,
                              but I'm also outside there, so any heat is very quickly dispersed.

                              Welding machines are a special category in the NEC, they allow a higher
                              current draw for a given wire size than they otherwise would, everything
                              else being equal. The reason, so I've been told, is that welding machines
                              are highly intermittent in their load, so the wires can cool off. This is
                              allowed, though, only when the machine is hard-wired to the circuit.
                              If the circuit is pluggable (i.e. you could plug something other than a
                              welder into it) then it has to be rated for the continuous load. (I don't
                              have an NEC, I'm not an electrician, but that's what I've been told
                              independently by a couple of real live electricians ... ymmv)