I presently have a 220V subpanel in my garage, the circuit is wired
with 6 gauge wire on a 60A circuit breaker.
This circuit is inside a 3/4" conduit. It is comprised of three 6
gauge wires (two hots and neutral, with conduit being the ground).
I now realize that choosing that low capacity was a mistake. (with a
big welder now in the picture) I would like to know just what would be
involved if I wanted to upgrade to 100A.
Can I be able to squeeze, say, two 4 gauge conductors (hots), plus one
8 gauge conductor (neutral), into a 3/4" conduit? Or will I have to
replace the conduit too?
I am very regretful of not doing the right thing and going for max
capacity. When I did it, the only 220V tool I had was a 3 HP
I have a 200A panel. The big loads that I may have is a 28A air
conditioner and a 50A kitchen range.
The garage circuit is used for my hobby stuff (compressor, welder),
and, as such, is used very intermittently. As you can guess, the
welder is also going to be used at a low duty cycle, it is not a
production style situation.
That's some data for me to ponder.
You could possibly squeeze two 4s and an 8 in 3/4" (39% fill) but if
there are many bends you will have trouble getting them in there.
That still only gets you 85 amps that you can "round up" to a 90a
breaker. 310.15(B)(6) does not apply to sub panels.
On the other hand, I wouldn't do anything until I had a problem.. I
ran a pretty big shop with a welder and AC on a 60a.
If you do upgrade, go to 125A, max allowed for a sub panel. Also note
the portion if the NEC pertaining specifically to electric welders and
Ieff which lets you undersize wire based on the duty cycle of the
(Just did the 125A upgrade thing myself)
I think the 60A you have is probably enough. Put the welder on a 50A
circuit; you can use 10 gauge wire as long as it's dedicated to the
welder (special exemption in the code for low-duty-cycle welders.)
You will seldom run the welder at its maximum current setting. On the
rare occasions that you do, turn off the air compressor -- IIRC from the
pictures you posted, it has a *big* tank you can charge up first if you
need compressed air and the welder at the same time.
Mine is actually 100% duty cycle at 200 amps, although I will never
run it anywhere close to 100% of duty cycle for any meaningful period
of time. With stick welding, the longest run time would for one stick,
perhaps 1-2 minutes, then I would need to change the electrode.
With TIG, it should likely be even less.
Yes, you are right 100%, I would definitely turn off the compressor if
I had to do big welding. You are also right that high amperages are
rarely necessary. With steel, I never had a need to go above about 150
amps, not that I have a great deal of experience. I never welded
aluminum, but people say that I need higher amoerages for that.
Anyway, do you know what NEC article 630 says about welder circuit
derating? I googled for a while and saw some references to that
article, but no actual tables.
Since your particular welder is rated for 100% duty cycle at high
current, the derating doesn't really apply. Use a 50A breaker and #6
copper wire (or, guessing here, #6 Aluminum SE cable.) If you are
popping the breaker, use a smaller electrode. :-)
BTW, you can use a 70A breaker in the main panel without increasing the
wire sizes if the wire is THHN, THHW, or THWN-2, and the breaker
terminals and the subpanel terminals are all rated 90°C instead of the
usual 75C. That would let you use a 60A breaker for the welder and
still have it trip first instead of tripping the feeder breaker in the
I seem to recall suggesting that you use 1" conduit when you posted
questions regarding the installation of your subpanel.
You can remove everything that you have already installed and put in a 100
amp subpanel circuit or you can run a new circuit just for the welder. The
book says that you can install 2-#4's in 3/4" emt. I think it would be a
tight squeeze with another conductor for a neutral.
Check the label on your main panel to see what is the maximum permitted
circuit breaker as that may influence your decision. The main panel may not
be rated for a 100 amp circuit.
I recommend that you pick up a copy of the National Electrical Code (NFPA
70) and figure out what your options are. You can buy the code book on
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