Tig welder extension cord

The business had a little extra cash before tax time so my wife let me buy a Thermal Arc 185 TIG welder.
I sorted out the plug/socket and installed an
outlet for the unit. I also want to fabricate a 20' extension cord for the unit, and that's where I got confused.
The welder specs call out 38 amps/240 volts as the max current draw. The welder comes with a line cord with 12 gauge conductors with a 50 ampere plug on the end. Anyone see the apparent contradiction here?
I installed a 50 ampere breaker, the called-out 50 ampere socket, and 50 ampere-rated conductors between the two. Should be no issue there.
The problem is the 20 foot extension cord. 8 or even 10 gauge portable cordage would seem to be a waste given the 12 gauge cord on the unit. OTOH, there's just something wrong about putting a 25 amp cable on a 50 amp breaker running to a 38 amp load.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

what was the duty cycle of the unit at max? probably 20%
so for 2 minutes out of 10 the 12 gauge cord has to carry a 38 amp load
then the cable has eight minutes to cool down
What is the cost of the cable compared to the cost of the machine?
is it really worth saving the 20 dollars on the length of the extension cord to use 12 instead of 8 Gauge? comapred to the 1500 to 2000 dollar machine and the even remote chance of a fire hazard?
In fact if youre feeling extra cautious cut the breaker down to 40 amps and you should still never manage to pop it.
For what youre saving on cable the safety seems a better choice
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jim Stewart wrote:

The national electric code allows the conductors supplying an electric welder to be reduced according to the duty cycle. You didn't really need to use #6 conductors to wire in the circuit -- but if you ever replaced the welder with one that had a much higher duty cycle machine you might have to put in heavier wiring, and with what you used you'll never have to do that.
I'd probably make the extension cord out of #10 SE cable unless I just really needed something more flexible. (I think it's available in 10 gauge.) There would be nothing wrong with using #12 SJO (etc) cord here.
HTH, :-) Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ratings for power cords are not the same as ratings for in the wall cables in conduits. The cable has more of a chance to cool from ambient air and dissipate the heat.
There is also a good point made by posters who mentioned duty cycle.
I am also not sure why there is a need for an extension cord. I would go with 10 gauge for the extension cord.
i
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jim Stewart wrote:

As has been noted, the NEC allows the use of undersized conductors on circuits feeding welders. This is ok in a commercial environment, but not so good in a residential environment. If there is a 50A outlet on the wall, someone will eventually try to connect a 50A load to it in a residential environment, so everything up to it really ought to be appropriately rated even if code doesn't require it. On the same idea, I would make my extension properly rated as well to allow for other uses in the future. Perhaps you'll get a kiln or heat treat furnace or something.
Pete C.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Besides worrying about the cord heating up, you should consider voltage drop. You don't want to have a sagging voltage characteristic when you are running the welder at maximum output. I haven't done the math, but you should. (And, of course, this has nothing to do with duty cycle,)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
>OTOH, there's just something wrong about

Actually you do this kind of thing every time you plug a table lamp wired with 18 gauge wire into a wall outlet protected by a 20 amp breaker. As others have mentioned, this is allowed by the NEC under certain circumstances. My only concern in your case would be voltage drop if your extension cord was too long. I also have a T/A 185 tig. It's on a cart along with a Thermal Dynamics 51 plasma cutter. The cart has a 30' 10 gauge cord that powers both the tig and the plasma cutter ( but not at the same time ). I've never had any problems with this setup. The 10 gauge cord never even gets warm, and neither unit seems to suffer from low voltage due to a voltage drop in the supply cord. Enjoy your new welder 42
--
Posted via a free Usenet account from http://www.teranews.com


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That is not a very good analogy.
i
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 04 Sep 2007 16:08:17 -0500, Ignoramus15584

Sure isn't, because the 1 amp table lamp is on a 7 amp cord in a 15 amp circuit.
However, when running a welder on an extention cord, you want a cord capable of handling AT LEAST 120% of the expected load to reduce voltage drop. I like a good tec table 4-3 or 12-3 extention cord (15 or 20 amp capacity) to run things like table saws, light duty welders,pressure washers, etc. A lighter cord can sometimes prevent popping a fuse on startup because it limits the load - but not a good idea. My old repulsion start table saw would occaisionally pop a standard 15 amp fuse when started plegged into the wall. When on a 16 gauge cord 25 feet long it took longer to come up to speed but never popped a fuse. Went to using "slo-blow_ fusetrons - no more blown fuses.
--
Posted via a free Usenet account from http://www.teranews.com


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 04 Sep 2007 18:48:18 -0400, clare at snyder.on.ca wrote:

Seems like a perfectly good analogy to me. The cord is sized considering the nature of the load, not the capacity of the circuit that's feeding it. The welder in question draws about 30A @ 30% duty cycle.

Unlike induction motors, most welders are tolerant of low input voltage. The 185T will operate on 208V circuits, so if it's being supplied by a typical 240V feed there'd have to be an awfully big drop to bother it.
--
Ned Simmons

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

My little "MIG" welder runs on a 15 amp circuit on 110 volts. On a 50 foot 16 guage cord at full output the voltage drops to about 96 volts. That reduces the maximum current of an already borderline welder significantly.(14% voltage drop roughly 28% power drop?????)
--
Posted via a free Usenet account from http://www.teranews.com


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
clare at snyder.on.ca wrote:

A TIG welder uses a constant-current power supply. It's much less susceptible to voltage drop in the power feed than a MIG welder (which uses a constant voltage supply).
Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 04 Sep 2007 23:28:21 -0400, with neither quill nor qualm, clare at snyder.on.ca quickly quoth:

Time to bite the bullet and go buy a 12/3 contractor's extension cord. They're about $60 here in the States. Dunno 'bout Canuckistan.
========================================================== Save the Endangered Bouillons from being cubed! ==========================================================
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 05 Sep 2007 04:54:26 -0700, Larry Jaques

I've already got a couple of them. I don't use the light cords anymore for anything with a full load draw of over about 7 amps
--
Posted via a free Usenet account from http://www.teranews.com


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 04 Sep 2007 23:28:21 -0400, clare at snyder.on.ca wrote:

In this case, a 20 foot, 12 ga extension with a 38A load @ 240V results in a 2.5% drop, or 234V at the welder. Also note that the 185T is an inverter welder - it acts like a switching regulator and draws more current as the supply voltage drops, so I doubt you'd notice any difference at the output.
I get about 30A running thru a 50ft, 16 ga extension for a 14V drop. Are you sure the whole loss is in the cord?
--
Ned Simmons

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Did you factor in both the power and the neutral? 100 feet of conductor in total.
--
Posted via a free Usenet account from http://www.teranews.com


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 05 Sep 2007 22:01:51 -0400, clare at snyder.on.ca wrote:

Yup. This calculator says 33A to get a 14V drop... http://www.powerstream.com/Wire_Size.htm
--
Ned Simmons

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You're assuming the conditions of setting the duty cycle of the welder also apply to the duty cycle of the cord. I don't see *any* reason to believe that's going to be the case. When I see a duty cycle rating for an extension cord, I'll believe that it applies to it. In the mean time, I'll use a cord rated for the peak load that it will be called on to handle.

I'll agree that this is a different, and almost unrelated, question.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 04 Sep 2007 21:34:16 -0600, Joe Pfeiffer

See the NEC article on welders. It recognizes the intermittent nature of welding and allows conductors with an ampacity lower than the breaker on a welder circuit.
There's a similar situation with motor branch circuits, though the rules for sizing the breaker and wiring are very different from than those for welders.
--
Ned Simmons

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You're right (and I'm surprised) -- the supply to a welder can be lower than called for by the peak current draw by roughly the square root of the duty cycle. Given that the duty cycle is defined over a ten minute period, this means you can run double the rated current through a cord for roughly two minutes! Yikes...
Though that's also assuming the welder doesn't have a specified I1eff rating -- if it does, that trumps the calculation.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.