115 volt plasma cutter power cords

[cpurvis]

Bought a Miller Spectrum 375 plasma cutter at work.

Fired it up yesterday, only to have it start tripping breakers almost immediately. Quickly isolated the problem: Circuit breaker for the line it was on was 20 amps; cutter can draw up to 28 amps. Seemed simple enough to correct, so I asked the electricians to install a 30 amp breaker.

The electricians correctly refused to do so. The branch circuit was originally installed per code: 20 amp breaker feeding a 20 amp outlet using 12 gauge wire. They pointed out that to install a 30 amp breaker and it's accompanying 30 amp receptacle on this line would make the wire the weak link in the system--it could overheat before the breaker tripped. Not only that, they said the power plug on the plasma cutter is only rated for 20 amps, not 28.

I could not believe that a manufacturer would intentionally install a 20 amp plug on a machine that needs 30 amps to run at full power. Not only is it too small, it won't even fit in a 30 amp receptacle.

I called the factory to hear what they had to say about it, and they seemed to not even really understand what I was talking about. Maybe I did a poor job of explaining, but the way they have this machine configured would encourage a person (particularly a homeowner or small business) to simply replace the 20 amp breaker with a 30 amp and thereby producing something of a fire hazard. That is the only way to get this thing to run at full power on 115v.

I wasn't satisfied with the response I got from customer service on the phone, so I wrote them an email explaining it. I haven't heard anything yet.

To fix ours, I'm just going to cut the plug off and switch it to 230v. However, I wanted the portability of a 115v machine. I guess that's out the window.

edit: Forgot to mention that a 30 amp line needs 10 gauge wire.

[Sandy]

I would imagine the same derating that is allowed in the NEC for welders also applies to plazma cutters. Neither are considered 'continuous duty' pieces of equipment nor appliances. Your electricians need to familiarize themselves with that section of the NEC.


Maybe I did a poor job of explaining, but the way they have this machine configured would encourage a person (particularly a homeowner or small business) to simply replace the 20 amp breaker with a 30 amp and thereby producing something of a fire hazard.

Myself, I don't subscribe to that mindset. A straight road and a V-8 might very well encourage speeding but the responsibility still remains with the operator.

[whateg0]

My previous MIG welder was wired with a 15A plug. The mfr states that it can be run from that circuit as long as the settings are correct. I suppose the same applies to the plasma cutters. If they show a max setting for running it on a 20A circuit, then it's okay for them to wire it that way.

Here's the problem with installing plugs and breakers that are rated higher than the wiring in between. It's easy enough for you, the current owner, to assign that circuit to the plasma cutter. If you died tomorrow and the next owner came in and saw the 30A plug and breaker, he'd likely assume that the circuit is wired for such. Then when the building burns down because the wire overheated, he'd learn differently.

People seem to lose sight of the big picture when doing stuff like this. It always seems easier to take the shortcut, until there's a mountain in the way.

Dave

[cpurvis]

I would imagine the same derating that is allowed in the NEC for welders also applies to plazma cutters. Neither are considered 'continuous duty' pieces of equipment nor appliances. Your electricians need to familiarize themselves with that section of the NEC.



Myself, I don't subscribe to that mindset. A straight road and a V-8 might very well encourage speeding but the responsibility still remains with the operator.

I might be going out on a limb, but I'd be willing to bet that our electricians are familiar with every section of the NEC.

And there is no way they'd wire it up so that 30 amps could pass through that 20 amp plug.


My previous MIG welder was wired with a 15A plug. The mfr states that it can be run from that circuit as long as the settings are correct. I suppose the same applies to the plasma cutters. If they show a max setting for running it on a 20A circuit, then it's okay for them to wire it that way.

Here's the problem with installing plugs and breakers that are rated higher than the wiring in between. It's easy enough for you, the current owner, to assign that circuit to the plasma cutter. If you died tomorrow and the next owner came in and saw the 30A plug and breaker, he'd likely assume that the circuit is wired for such. Then when the building burns down because the wire overheated, he'd learn differently.

People seem to lose sight of the big picture when doing stuff like this. It always seems easier to take the shortcut, until there's a mountain in the way. I'll have to look through the manual again. I only remember seeing a blurb about "you may need to upgrade to a 30 amp circuit to run full-blast...." but that would really eliminate the fire risk because the 20 amp plug won't plug into a 30 amp outlet.

[Broccoli1]

"If the unit is operated from a 30* ampere, 115 volt circuit or a 15** ampere, 230 volt
circuit, a different input power plug must be installed on the power cord. See
Section 4-9 for instruction."

It is all explained in the manual regarding changing the PLUG:)

[Broccoli1]

I called the factory to hear what they had to say about it, and they seemed to not even really understand what I was talking about. Maybe I did a poor job of explaining, but the way they have this machine configured would encourage a person (particularly a homeowner or small business) to simply replace the 20 amp breaker with a 30 amp and thereby producing something of a fire hazard. That is the only way to get this thing to run at full power on 115v.


They absolutely do not encourage or even suggest just changing the 20A CB to a 30A CB.

In fact all they state is that you will need a 30amp individual branch circuit.:)

If a homeowner or or small business does not understand what this is, then they should consult a sparky.

[MAC702]

There's no danger with an electrician being unaware of the allowances for welding machines, because it just means he'll be overly safe.

But, yes, this machine CAN be on a DEDICATED receptacle and have the 20A breaker changed to a 30A. This would make it a 30A branch circuit that has the wiring rated according to NEC Section 630 for welding equipment.

The underwired 30A circuit should be labeled "welding equipment only" so the aforementioned next owner problems (and your own forgetfulness) are minimized. And it should really only be done in industrial settings anyway, but it is still legal and okay in residential, just be good with the labeling and don't leave it that way when you move out.

Obviously, if the circuit feeds more than one receptacle, you can't just change the breaker; that's what a dedicated receptacle means.

And the same derating rules apply generally to the plug and input cord from the manufacturer, which is why the machine can have a 20A plug (which can safely pass much more than 20A anyway, it's just a "20A" configuration.)

[cpurvis]

Got a response today.

Their explanation is: If you square the input amperage, then multiply it by the duty factor, then take the square root of that number, the result is 16.57 amps, which is less than 20. Hence, the 20A plug is OK.

I will try to explain this to the circuit breaker tomorrow but I doubt if he'll believe me that he really isn't seeing 20 amps.

[MAC702]

...Their explanation is: ....

Interesting. That isn't the formula in the National Electric Code.

And it really WILL pull its maximum amperage through the wiring (and circuit breaker.) That's not the issue. The issue is that the machine is not capable of doing it for very long, so there is a built in limiting factor on conductor temperature rise. Therefore, in a dedicated welding equipment receptacle, you are permitted to have a larger breaker on smaller wires/plugs, using the formula in NEC Article 630.

[hankj]

I will try to explain this to the circuit breaker tomorrow but I doubt if he'll believe me that he really isn't seeing 20 amps.

CB's do get tired. The one you have may be near the end of it's udeful life as an overcurrent protective device! You could try replacing it....

Hank

[Tom37]

I was getting ready to post pics of the cuts I made with my 375 x. Now maybe it was just the LWS where I purchased but they told my to look at the settings and when using 110 to keep the sttings in the 110 range, making a point to show me the white ring around the dial that says 110. Also said the only way to reach full power was to run on 220. I personally have only a days experince with the plasma, I am only reffering what I was told. As with anything new I havent sat down and went thru the details of the manual yet. Good luck.

[cpurvis]

I thought it was odd that I didn't remember seeing a white '110V' ring on our cutter, so I checked today.

There is no such ring. There is a white ring, all right, but it goes all the way around the dial and says nothing about line voltage. In fact, there is no printing associated with it at all.

Anyway, our problem is solved. It is now running happily on 230V.

[Sberry]

Its not unusual for electricians to miss 630.11, happens all the time. As Mac said, a 30 is allowed on a single wire single recept circuit dedicated to this machine. Personally it would run from 240, on some occasion I would convert if I had to for special job but its usually a moot issue as the machines tend to sit at home, often the need for portability is often over rated.

[TOMWELDS2]

I just dont like the fact that the company's are pushing to sell this stuff to 'homeowners and hobbyist'. Having a 20amp recep on a 30amp line, even labeled, in a residence, isnt a bright suggestion for a manufacturer. That's commercial stuff. ...NEC 'correct', application 'wrong'..IMHO. Me, i'd chop the plug, make it a 30amp. Not saying for anyone to do that, but i would. I would hate to see 'their suggestion' on some old rubber wiring! Bad news..
I just ran some welder outlets for a buddy of mine in his shop...50amp recep's, #8 wire and put a 30amp and a 50amp breaker in the panel. When he mig's, it's on the 30 and when he sticks, he puts it on the 50. I did this because his guys use extension cords and when it gets cut (and shorts), the breaker trips 'quicker'...lol...I try to design things for the 'real world' rather than 'duty cycle'.

[wmgeorge]

Its not unusual for electricians to miss 630.11, happens all the time. As Mac said, a 30 is allowed on a single wire single recept circuit dedicated to this machine. Personally it would run from 240, on some occasion I would convert if I had to for special job but its usually a moot issue as the machines tend to sit at home, often the need for portability is often over rated.

It depends on the rated Duty Cycle of the welder, and unless its been changed in the 2008 code you need to change the receptacle and plug both to a 30 amp and label. Hardly worth the effort when it can be changed to 230 volts.
Oh, forgot to add this until today, as far a portable don't forget you need a pretty hefty air compressor to run the plasma cutter. I don't remember the minimum CFM you need but I had at one time just a 1 HP portable one and it ran a lot.

[Sberry]

It depends on the rated Duty Cycle of the welder, and unless its been changed in the 2008 code you need to change the receptacle and plug both to a 30 amp and label. I doubt this is something that would get changed but where in the code is this? There are specifically exceptions for welding machines for it. I believe one is in 210.21 and 406 refers to it.

[Sberry]

It was never meant to run wide open on a 20A circuit.

[wsy]

/Read the fine print in the manual for the /spectrum 375.

It requires 20 amps at 110VAC; the 28 amps is the output current
after the stepdown transformer.

Yes, I have one, and yes, if I run it at full power I occasionally pop
the breaker (more often lately; the breaker is getting "soft"), especially
when I have a worklight plugged into the same circuit.

but- it does work fine and the current is under 20 amps while cutting at
maximum power.

- /bill

[Zrexxer]

/Read the fine print in the manual for the /spectrum 375.

It requires 20 amps at 110VAC; the 28 amps is the output current
after the stepdown transformer.That's funny, 'cause that's certainly not what the manual says:

http://www.hobartwelders.com/weldtalk/attachment.php?attachmentid=26635&stc=1&d=1214965080

[hankj]

[QUOTE=wsy;328842It requires 20 amps at 110VAC; the 28 amps is the output current after the stepdown transformer.....- /bill[/QUOTE]

:confused:

Bill, you gotta 'splain me how that machine can put out more power than it uses!

I'm an old dog electrician, 'n I can't recall ever seeing that phenomenon.

Hank

[RandynTx]

I'm new here. This is my first post but perhaps I can shed some light on fixing your electrical problem. I understand your problem because I just purchased a Hobart 400 Air Force and I have the exact same situation. It's not as complicated as it may seem.
I have chosen to go with a 230/240 connection because in my understanding this will give you a better quality cut. Also, trying to find a 110/115 connection like the one required by your machine in just any old place will be almost impossible. There's not very many places that have this type of 110/115 connection readily available.
Your electrician was absolutely correct. However, it doesn't sound like they fully explained the situation to you. You CAN NOT just change the breaker and the recepticle if the wire between the breaker and the recepticle is not large enough (in this case you would need at least #10 gauge wire.)
Please understand: the wire between the breaker and the plug recepticle is what is in question here. NOT the wire in the cord that was supplied with your machine. The cord that came with your machine is perfectly capable of handling any 110/115 or 230/240 connection.
Here are you choices:
#1) Go with a 230/240 connection. Have your electrician run a new line with a minimum 230/240v 30amp breaker (forget about the 15amp breaker. It is listed as minimum and you will be kicking the breaker constantly).
Then change the plug on your machine to match the plug recepticle that the electrician installed. Make sure the change over switch is set to the correct voltage. You're ready to go.
#2) If you must have a 110/115 connection (although I still suggest you go with a 230/240 connection) have your electrician run a new line with a 110/115v 30amp breaker and #10 gauge wire and a 20amp SINGLE recepticle. The 20amp SINGLE recepticle on the 30amp breaker is acceptable in most areas of the country because you can only plug in one item at a time. This way you don't have to replace the plug on your machine.
If for some reason this is not up to code in your area you will have to have a larger 110/115v recepticle installed and change the plug on you machine to match that recepticle. Again, make sure the change over switch on your machine is set to the correct voltage.
Hope this helps. Good luck.

[Broccoli1]

Welcome Randy-

"But, yes, this machine CAN be on a DEDICATED receptacle and have the 20A breaker changed to a 30A. This would make it a 30A branch circuit that has the wiring rated according to NEC Section 630 for welding equipment."

mac explains the reason back in post #7
:)

[hankj]

I doubt that Art. 630 could be used in this case, anyway. If there are multiple outlets on this circuit, as is the usual case for a 20-amp branch circuit in a dwelling, 630 is not applicable.

However, if in fact this is a single receptacle circuit, then the breaker can be changed to a 30 amp for the reasons specified in Art. 630, Table 630.11(A).

Hank