sevilla
Silver Member
Hi, I'm considering to buy a welder. My first choice would be a stick welder like the Miller Thunderbolt 225/150 AC DC. My question is how many Amp must the electrical outlet (and the breaker) be? Thanks.
Breaker/outlet Amps for Thunderbolt 225/150 AC DC
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Inspector507
Super Member
You're probably looking at a 50A 2 pole 3 wire outlet
without a serial number i can't be positive, but i did a quick look at the miller owners manuals for the thunderbolt series, and for 230v under full load, it looks like the maximum current draw would be 47.5a, so you would want a 50a breaker. for probably 95% of your standard stick welders owned by weekend warriors, you're going to be looking at a 50a max draw, so this falls right in line and sounds pretty reasonable.
you certainly need a 50a breaker, and for that, the normal wire size would be awg 6 (copper). this will support a 50a draw under 100% duty cycle. welders don't generally have 100% duty cycles, so there are exceptions to the wiring codes to allow smaller wiring, but i don't know what is allowed in your area, and even so, using that wire size reduction requires marking the receptacle for its use. to be honest, better to just use #6 copper and have a 100% duty 50a circuit.
i'm not an electrician, but i've done a lot of work to two homes i have owned - often replacing poor work done by others, so i've learned a lot as i go. if you're not confident in this area of expertise, get some qualified help, as there's no guarantee my knowledge is correct
yomax4
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40 amp and 50 amp breakers are the same price. I'm sure you have a 100 amp service at least. Go 50 amp for now and the future.:thumbsup:
smfcpacfp
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According to the Miller Service Manual for your proposed welder, if you have a time a delayed circuit breaker 50 AMP, for a normal circuit breaker 70 AMP. They describe these as the maximum that you would need. It is a little confusing, so check it out yourself. I found the simple solution when I got my Millermatic 211 was to call Miller technical support and talk to a person.
CharlieS
Gold Member
The proper way to size a breaker is rated amp load X 125%. The reason for this is circuits must be derated to 80% for continuous duty use. Thus the previously mentioned 47.5 amp load x 125% = 59.375 amps or a 60 amp breaker. (Thus 59.375 x 80% = 47.5)
Also dont forget to size conductors to the welder plug accordingly. 60 amps would require a minimum #6 copper or #4 aluminum. For long runs some voltage drop adjustment may be required also.
Also dont forget to size conductors to the welder plug accordingly. 60 amps would require a minimum #6 copper or #4 aluminum. For long runs some voltage drop adjustment may be required also.
Mark @ Everlast
Advertiser
Duty cycle limited machines have different rules. Actually much lighter gauge wires can be used in duty cycle limited machines. Breaker sizing is also a little different. If I can find the link to some of the info from the NEC, I will post it.
patrick_g
Elite Member
I have always used 50 amp breakers on my Lincoln AC/DC Tombstone and pretty much ignore duty cycle. So far so good. Welder is at least 15 years old and works just like new A N D I have NEVER popped a breaker with it.
(Side note... I treated my Lincoln WeldPak 100 (MIG) the same way for 15 years, welding till it shuts itself off and doing it again when it lets me. A couple days ago it started acting "funny" and sounding weird (noisy airy arc) and I suspect the rectifiers are fried making it have AC output.)
Pat
(Side note... I treated my Lincoln WeldPak 100 (MIG) the same way for 15 years, welding till it shuts itself off and doing it again when it lets me. A couple days ago it started acting "funny" and sounding weird (noisy airy arc) and I suspect the rectifiers are fried making it have AC output.)
Pat
breakers and duty cycle aren't really the issue. your breaker must be able to resist the entire current draw that you are putting on it, otherwise it will trip. the downsizing issue is about the wire you use between the box and machine. this is where you can downsize due to duty cycle. normally, a 50a load requires #6 wire, but wiring does not fail instantly the way that a breaker trips instantly when overloaded. the wire will get hot over time and then eventually cause failure and possibly a fire.
since welders generally have a duty cycle (10%-60% generally), meaning that they will only work (draw current) for so many minutes in a row. because of this, the current draw will cause a smaller wire to heat up, but not to the point of failure. when the machine hits its duty cycle the draw stops, and the wire will cool down. a properly sized smaller than normal wire will work fine for this application.
this may seem a little sketchy to some people who have never heard of it, but i can tell you that it is a common occurrence. i have an older craftsman 30a-230a welder, and the power cord that the manufacturer put on it is a 12/3. normally people consider a #12 wire to be good for only 20a, i can guarantee the welder draws more than 20a at times. as you can see the manufacturers are already doing the wire downsizing, so it is perfectly common and safe. i think i remember reading somewhere that most common stick welders will operate safely on 10/2 nm cable.
again, this is just my layman's description of what happens. if unsure, always consult a professional. i do know that to meet code, you need some special sort of labeling on any circuit where the wire is downsized due to duty cycle.