According to krw :
Thanks for the tip. But what does SO and SJ mean?

It's a rubber jacketed stranded wire cable. I believe SO insulation is
rated at 300V, where SJ is 600V. For 220V (8/3 w/ground) operation, I
think you need SJ.

SJ is medium duty. SO is heavy duty. SOW is "heavy duty, wet
locations".

SO is to be preferred. I'd only recommend SJ if the welder was
going to be stationary, and you can keep the cord out of the way
of getting cut/hit/splattered/walked on.

The heavy-duty "contractor duty" extension cords[*] you find at the
Borg are SO or SOW.

SJ is the step below "contractor duty", and a step above the thin
orange-ribbed stuff (light duty). Zip cord is a step below the
orange stuff ;-)

You don't need /3 for a welder. /2 will do. /3 in flexible cord
is pretty exotic stuff (combined 240/120 devices) except for 4 wire
ranges and dryers (preassembled cords).

[There's actually a whole host of "S" series specifications. S, SO,
SOW, SJ, SJO, SJOW etc. SJ prefix are medium duty. The "S" are
heavier. O means outdoor (ie: UV/freezing resistance). W means
wet. etc.]


What would you guess 25' is going to cost?

If you have to ask, you can't afford it. ;-) I bought some 12/2
w/ground SO at the BORG last weekend for a little over $1/ft. I'd be
surprised if 8/3 was less than $6/7 per foot.

A welder isn't going to need /3. It sounds like SO (or SJ)
8/2 would be the best choice.

I _suspect_ you'd pay around $3-4/foot for SO 8/2. Some years ago,
I paid $1.50/ft for SO 10/2.

Keep it as short as you can get away with.

NOTE that "Northern" (aka "Northern Hydraulics") probably has
welder replacement cords for a bit less than you can cobble them
together yourself.
[*] The fat things that come in all sorts of pretty colours, massive
molded connectors, and cost an arm and a leg.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.