Upgrading garage circuit to 100A?

[Ignoramus18798]

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 vertical compressor.

i

[Toller]

Can't answer your question (at least not without looking it up...) but wonder if you have the electrical capacity in your panel for a 100a sub.

[Ignoramus18798]

Good question.

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.

i

[gfretwell]

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.

[Ignoramus18798]

The bends that I have are all open kind, that is, there is either a 90 degree turn with removable back cover, or a junction box.

Thanks... Maybe I will just follow your advice. I am not going to weld bridge sections or oceangoing ships.

i

[hallerb]

remember too that 60 amp main is really 120 amps at 120 volts.

just avoid running everything at the same time and you should be fine

[Ignoramus18798]

Well, if I run my welder at 200 amps, the 60A breaker trips after a few seconds (like 10 seconds or so).

i

[Pete C.]

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 welder.

Pete C.

(Just did the 125A upgrade thing myself)

[zxcvbob]

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.

Bob

[Ignoramus18798]

I tried to find article 630, could not find it, but will keep looking. Mine is 100% duty cycle at 200A, and 60% at 300A (the latter is my assumption). Good idea, thanks.

i

[Ignoramus18798]

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.

Thanks!

i

[zxcvbob]

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 house.

Best regards, Bob

[John Grabowski]

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 Amazon.

[PipeDown]

And that assumes the run is not too long or through a very hot area like an attic in which case you would need to further derate the ampacity of the conductor.

>

[Steve Barker LT]

the 60A circuit is more than enough for all the the hugest of welders. We ran a detached garage with a 250A welder on a 10ga 30A underground circuit for 30 years. How big a welder do you have?

[zxcvbob]

From his descriptions, I'd guess it's a 400A TIG welder. But that doesn't mean it won't operate just fine on a 50A or 60A circuit; he just can't crank it up all the way.

Bob

[Ignoramus8797]

Your memory is excellent, and I was wrong.

Got it. Perhaps staying within my current setup is the wisest choice.

Will do.

Thanks John.

i

[Ignoramus8797]

The area is all cool, but the run is long. However, all turns are "open" (go through a corner or junction boxes).

i

[Ignoramus8797]

It is actually 300A. It operates off my phase converter. I think that one of the issues with it is that it has a bad power factor, also. I tripped my 60A breaker at 200 amps.

i

[gfretwell]

My trusty old 230a buzz box has been running happily on a 30a circuit for 40 years at any setting