extension cord for my MM 135

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my question on this is i heard its not good to use an extension cord.  why is that?  ive used a 10 guage cord thats 10 feet long with my welder and noticed no problems.  now if i use a cord of the same guage or bigger and rated for the same ams or more how would it hurt the performance?  my outlet in the garage has what looks to be 14 or 16 guage wiring and a 30 amp fuse at the braker box.  the cord on my mig is 14 guage and (i think)20 amps.  going with a considerably larger extension cord seems like it would be just fine considering my outlet is maby 14 guage if that.  when i weld i only run the welder on the outlet and nothing else is plugged in to be on the safe side.  i check the outlet to see if its getting hot and its barely warm if that.
Reply:You're right. There is no problem using an extension cord, as long as it is not too long and it is of the proper gauge.  When you get to 50 or 100' you'll get a drop in voltage which is harmful to the machine in use. The cord length and gauge you described are actually overkill for your application. It will hold out much longer than your duty cycle will allow you to continue welding.Hobart 140 Handler w/ gasHyperTherm Powermax 380 Plasmaoxy/acetylene
Reply:i would like to use a 20 foot cord.  so if i get a cord the same guage and amps as the machines cord ill be fine?  ill go 12 guage if needed.  the 10 guage was for my air compressor.  it wouldnt run with anything less than a 10 guage.
Reply:The same would be fine at 20', but I'd go with the 12 gauge myself to be sure.Hobart 140 Handler w/ gasHyperTherm Powermax 380 Plasmaoxy/acetylene
Reply:Rick has it nailed pretty good. The big problem arises when guys pick up those 25's, 50's or 100's out of the bargain bin. Most of those cheapos are 16awg or even 18awg. Heck I've even grabbed a 100 ftr because it was only two bucks more than a 50 ftr. The saw might moan and groan a little more but gets the job done. Your welder won't perform well like that.I think the message is; if you need a cord for your welder get a decent one with some beef and not a whole lot longer than is needed.  A 10awg cord should reach a ways for you tho.
Reply:Your 10AWG cord will be just fine for that welder.  Heck, you could use 10AWG and run a 100+ foot extension cord for that welder and be fine.  Look on page 15, section 4-7, of your owner's manual for the wiring recommendations (Miller says you can use 12AWG for a 50 to 200 foot extension cord).  All of that is for the 115V model.  If you have the machine/model wired for 230V, then your wiring recommendations are similar but Miller recommends a shorter maximum wiring length.And as folks have said, the problem with long or skinny or long/skinny extension cords is voltage drop over the length and also overheating of the cord during use.  Overheated cord melts or burns (neighbor had a long extension cord on a cord reel and was using it for something without taking the cord off said reel, he melted and then fried the cord from heat and then shorting out).  Too much voltage drop and the machine (saw, welder, etc) at the end of the extension cord doesn't get the proper voltage it needs to run right and so it 'loses power'.And you shouldn't or better not have a 30amp breaker wired with 14 or 16 AWG wire!  If your garage outlet is a 'standard' 15amp 120V one, it should be wired with 14AWG wire and be on a branch circuit with a 15 amp circuit breaker (US and Canadian standards, other places -may- be slightly different but I don't think so).  There is -NO- wiring (in the walls, conduit, etc) that could be thinner than 14 AWG on a branch circuit.  The wires or cords to/in a device MAY be thinner, depending on the device (16 or 18 AWG wire is common on devices that don't draw a lot of current during use, like household lights, small appliances, etc).And remember that the bigger the AWG number, the smaller/thinner the wire is (just like sheet metal gauge, bigger gauge means smaller/thinner).
Reply:well the outlet in the garage never got hot.  my air compressor is a 100 unit with a 10 guage cord.  it blows the 30 amp fuse if i plug it in and the the switch is in the on position.  but if its in the off position it don't ever blow the fuse.   i don't skimp on cheape extension cords. thats why i got that 10 guage but i need it to be at lest 5 feet longer.  20 feet would be perfect.   guess ill pick up a 20 foot 12 guage.   thanks