Welder Extension Cord

[deereman75]

#8 is good from 58A up to 89A according to the calculator at 240 V, copper.

once again there no minumum amperage you can run a cable at, otherwise you could never turn a machine off.

 

[grsthegreat]

#8 is good from 58A up to 89A according to the calculator at 240 V, copper.

no, don't care what the calculator shows. The national electric code states ....unequivocally... the following

#14 - max 15 amps
#12 - max 20 amps (although the tables allow up to 30 amps, but law wont let it happen)
#10 - max 30 amps
#8 - max 40 amps
#6 - Max 52 amps
#4 - max 69 amps

All these figures are for wires rated at 60C (140F) which is how most extension cords are rated. Exceptions for wire rating depend on the type of wires involved. It doesnt matter if your working 120 v, 240 v 277 v or 480 volt these figures never change.

Now where it gets real crazy is that there are a few exceptions: that being for wires feeding a service or subpanel. Then #4 will be allowed to carry 100 amps.

The actual charts on wire carrying capacity involve probably 20-30 pages in the NEC code book, and it gets real complicated to figure it out sometimes.

 

[grsthegreat]

And heres a final note to really throw you for a loop. Manufacturers don't have to follow the NEC. Thats why you'll see a limp fixture with 22 Gage wire... real micro fine wire ... that plugs into a 15 or 20 amp socket. That wire is probably only rated at 5 amps, but they get away with it. Ive seen 5 HP air compressors with #12 pigtails /.... WAY undersized but thats how they were shipped.

If you look inside an electric water heater you'll find that the innerds are wired in #12 wire HOWEVER electricians are required to wire up to it with #10 (larger ) wire. Makes no sense at all.

Public utilities are also immune from the NEC. I reciently wired a 400 amp comercial building with an overhead service. I had to run Parallel 350MCM COPPER feeders up 20' of 3" rigid riser pole thru the weatherhead. The utility company dropped a wire about the size of a #6 aluminum wire to connect their side of things. According to the code book, that wire ig good from the range of 40 - 60 amps, but there powering up a 400 amp commercial shop with it, Their lineman just shook his head and told me if it proves too small they'll up-size it later on. No codes and no inspection on their end.

 

[Inspector507]

no, don't care what the calculator shows. The national electric code states ....unequivocally... the following

#14 - max 15 amps
#12 - max 20 amps (although the tables allow up to 30 amps, but law wont let it happen)
#10 - max 30 amps
#8 - max 40 amps
#6 - Max 52 amps
#4 - max 69 amps

All these figures are for wires rated at 60C (140F) which is how most extension cords are rated. Exceptions for wire rating depend on the type of wires involved. It doesnt matter if your working 120 v, 240 v 277 v or 480 volt these figures never change.

Now where it gets real crazy is that there are a few exceptions: that being for wires feeding a service or subpanel. Then #4 will be allowed to carry 100 amps.

The actual charts on wire carrying capacity involve probably 20-30 pages in the NEC code book, and it gets real complicated to figure it out sometimes.

You and I usually agree on what the NEC says you can do. However this time I have to disagree on a few things.

The NEC does not cover extension cords, period. UL and other testing laboratories probably follow the amperage charts listed in section 400 of the NEC when writing their standards. But the NEC does not cover cord assemblies.

There are several cases where the conductor sizes you listed can be protected at a higher amperage than what the charts you are reading says they can be. Look at the asterisk for 14, 12 and 10 wire listed in Table 310.16. The asterisk says to look at 240.4(D). 240.4(D) refers you to sections 240.4(E) through (G). 2404(G) is for Specific Conductor Applications. Notice the chart there? Air Conditioners, welders, motors and so on have different rules for ampacity. Some welder conductors can be fused at 200% of their ampacity. Some motor conductors can be fused at 800%. So 310.16 is for general wiring, but there special exceptions for certain conditions.

 

[grsthegreat]

You and I usually agree on what the NEC says you can do. However this time I have to disagree on a few things.

The NEC does not cover extension cords, period. UL and other testing laboratories probably follow the amperage charts listed in section 400 of the NEC when writing their standards. But the NEC does not cover cord assemblies.

There are several cases where the conductor sizes you listed can be protected at a higher amperage than what the charts you are reading says they can be. Look at the asterisk for 14, 12 and 10 wire listed in Table 310.16. The asterisk says to look at 240.4(D). 240.4(D) refers you to sections 240.4(E) through (G). 2404(G) is for Specific Conductor Applications. Notice the chart there? Air Conditioners, welders, motors and so on have different rules for ampacity. Some welder conductors can be fused at 200% of their ampacity. Some motor conductors can be fused at 800%. So 310.16 is for general wiring, but there special exceptions for certain conditions.

The asterisk is used to allow the wires to be used at their higher rating when you run multiple conductors in a conduit. For example, if i run 6 Current carrying conductors in a conduit i have to derate wires to 80%. This chart allows me to use the higher 29 amp rating for #12 then derate this to 80%.

There is a convention in the NEC that limits #14, #12 and #10 use, but i don't recall the actual wording...ill have to go look it up.

As for the extension cords, they were controlled in the last code changes...again id have to look up the actual referencer. We discussed this in my last code upgrade class 3 years ago *need my 2011 classes this fall). Also at that time, the NEC regulated us to 60C side of chart unless wires were specifically rated higher. By convention, the inspectors here in Idaho and wash state follow the 60C side of the chart....I don't necessarily agree, but i am forced to follow it.

 

[Inspector507]

The asterisk is used fto allow the wires to be used at their higher rating when you run multiple conductors in a conduit. For example, if i run 6 Current carrying conductors in a conduit i have to derate wires to 80%. This chart allows me to use the higher 29 amp rating for #12 then derate this to 80%.

My bad, I had an old code in front of me. Looking at the 2011 online now, check the ampacity chart 310.15(B)16 which was formerly 310.16. It is now a double asterisk which refers you to 240.4(D).

The derate chart for conductors you referred to is 310.15(B)(3)(a). That's not what we're discussing here.

 

[grsthegreat]

My bad, I had an old code in front of me. Looking at the 2011 online now, check the ampacity chart 310.15(B)16 which was formerly 310.16. It is now a double asterisk which refers you to 240.4(D).

The derate chart for conductors you referred to is 310.15(B)(3)(a). That's not what we're discussing here.

oN THE BOTTOM OF THE b310.3 CHART (2008 AS MY 2011 BOOK IS OUT IN WORK VAN) THE ASTRIX STATES THAT UNLESS SPECIFICALLY PERMITTED ELSEWHERES IN THE CODE (AGAIN IT WOULD DEPEND ON THE SITUATION) tHE OVERCURRENT PROTECTION of these conductors is
14 g = 15 amps
12 g = 20 amps
10g = 30 amps

Stupid caps key strikes again
I'm sure there are some exceptions, but they wont apply to things like shops and welders. Those need to follow these guidelines. I stated elsewheres that the #8 will prob be fine for the wiggle box welders used in a residential shop. But just try and get away with that on a commercial job and you'll be doing some rewiring.

Homeowners and farmers have been getting away with running heavy motors and welders on small extension cords for years, and I'm sure they work just great. But we in the trade have to rely on this stupid stupid book that gets worse every year.

 

[Inspector507]

I'm sure there are some exceptions, but they wont apply to things like shops and welders. Those need to follow these guidelines.

Yes it does apply to welders. The pictures attached are from the 2011 NEC and the same as in the 2008.

Riddle me this............how did I get by with running #10 to my 50A welder receptacle attached to a 50A breaker? Because Section 630 in the NEC allows it.

 

[crazyal]

I'm not an electrician nor do I know most of the codes. But why would NEC even deal with extension cords (not trying to be sarcastic, I would just like to know)? I could understand if the NEC was talking about an extension cord made by an electrician (say for job site power).

I have to believe that a company would hire an engineer (not an electrician) to calculate the load, duty cycle, and voltage drop to design any product, whether it be a welder or an extension cord.

 

[dstig1]

#8 is good from 58A up to 89A according to the calculator at 240 V, copper.

There have been several posts since you wrote this which should make it clear, but it is not code. I am going from (faulty) memory that is a few codes old, but I thought 8 ga Cu was rated for 45 A and 6 Ga was rated for 55A, per NEC. Then the code further says that if there is not a breaker at that size, that you are allowed to step up to the next available standard size breaker. Which would mean (if my recollection is correct) that 8ga could be run on a 50A breaker and 6ga on a 60A breaker. For a short run that would probably be fine, but I wouldn't do it for a long run as voltage drop would cause issues.

Then there is the issue of de-rating for welders. Which is probably why they sell 8ga extension cords with 50A plugs on them. Nobody using them would ever reach any sort of overheating capacity issue. If you need 400A, you have big service already...

 

[eastexan]

I found a heavy extension cord where I used to live that someone had left behind. It had a 50amp receptacle on one end and a 30amp plug on the other for plugging into a dryer outlet. I have used it at times for welding projects away from my shop and close to my house.

Last May, I used the extension cord in welding some 3/8" plate to some 1/2" angle with 5/32" rod to make a weight box for the front of my tractor, and it all went fine.
But the other day, after reading about welding extension cords, I got curious and decided to open the receptacle end up and see what size wire was in there.
I was surprised to see that I had been doing all that welding with 12/3 with ground. Of course the neutral wire wasn't hooked up, but that extra wire in the cable made it fatter and look as though it had bigger gauge wire than it actually had.

But the bottom line is that it worked fine, and when I rolled the extension cord up afterward, I never noticed it being hot.
I guess the reason being that I took my time between rods in chipping slag and wire brushing and kept within the welder duty cycle, and nothing got overheated.

If I had known it was only 12 gauge wire, I probably would have never even tried it. I've used both my Idealarc and Thunderbolt on that cord and hope the machines weren't hurt in any way, but I think they're fine.

 

[J_J]

How much difference would the voltage make in the selection of wire gage? Is it not true that as the voltage goes higher, the gage of the wire could change to a smaller gage wire. For instance in Jacksonville, I read a voltage of 240 , so does that make up for any voltage drop caused by the gage of wire? The machine calls for 208V.

I don't care to argue about the wire size, but when someone puts up a chart with diameter of the wire, the resistance, open wire, covered wire, length, what good is the chart/tables?

You ask 5 electricians about what size wire, and you get several answers. You could use this, you can safely use this, You must use the wire only, etc.

Some of the cords specify 2 #8 with #10 ground, don't understand that either.

Yes, I see the 50 ft cords with #8, but with a 50 A plug, and I am guessing for safety, not capability.

What current should #8 wire carry, in an extension cord.

The cord to my plasma cutter has #8

Can I get away with plugging it into #10 wire. I have only been using it that way for about 8 years, but was I totally unsafe?

I have been meaning to measure the current on the #10 wire at my max plasma cutter setting, using a Fluke amp meter.

 

[Lightnsound]

Some of the sources being used to find the data are questionable. A copy of the NEC or a $14 copy of Ugly's is the way to go.

Ampacity is ampacity, regardless of voltage. The insulation on the wire must be rated at or above the voltage being used, but an amp is an amp and it doesn't matter what the voltage is when determining the wire gauge.

 

[Short Game]

I came into a bunch of 6 and 8 cable and built various extensions to give me options for my 220 needs.

This one comes straight from my panel and is where my welder used to be. I back-to-backed two outlets on a scrap of plywood. It was interesting to find that some Leviton outlets of various amp ratings were identical inside and only the way the slots were made in the plastic was different.

I inherited this setup and added a second 220 pattern. I run my welder on that 30 amp breaker and never trip it, even when the compressor fires off at the same time. It's on a 2X6 with a screw eye at the top for hanging it. The cable is 60 feet of 8 gauge. One of the plugs goes to my disc sander and the other to my next extension, with the welder and compressor plugged in there.

This is the latest one I built and is way handy.

Luckily I'm not in business and won't be getting stuff disallowed (yet). All the connection points are soldered and solid. I know it's all good, and that's good enough for me.

Most of the outlets were gotten from garage sales and thrift stores for fifty cents or a buck, as were the 6 gauge plugs.

 

[eastexan]

Short Game, looks like you have a real handy setup. :thumbsup:

 

[JB4310]

Well I can understand how this topic has caused some division.

I checked my Miller ac/dc machine today, I knew the power cord coming out of the box was fairly small, but was shocked to see it's only a 12/3 wire :confused2:

Says right on the front cover it requires 47.5 amps, so of course I wanted to do the circuit legit and have a 50 amp breaker with 6 gauge wire to the 50 amp outlet. So I guess you could safely use a much smaller extension cord, probably get away with a 10Ga if not going to far???

Like I mentioned I have a monster 50+ foot, 6/4 cable, I got it for free, but if I paid what it would really cost, I might feel kinda foolish finding out it is way overkill. Mine doubles as a whole house generator feed, so I do need the heavier cable. My genny now is 10kw and has a 40 amp breaker, so I guess that 6 ga cable could handle 12kw or maybe more generator.

JB.

 

[J_J]

I saw this wire gage chart, does it have any value?

.

 

[JB4310]

I saw this wire gage chart, does it have any value?

.

I don't know, But it shows 6 ga wire needed for 20 amps at 30 feet

This chart is at the other end of the spectrum from what you referenced before.

Maybe I'm not reading it right???

JB

 

[dstig1]

Every power tool/welder these days has a similar chart in the owners manual telling you acceptable extension cord sizes by length. Easiest thing to do is use that. It would be different for 120v vs 240V as the voltage drop would be worse on the lower voltage.

 

[MikeD74T]

.....Ampacity is ampacity, regardless of voltage. The insulation on the wire must be rated at or above the voltage being used, but an amp is an amp and it doesn't matter what the voltage is when determining the wire gauge.

Sorry, that's just plain wrong. A watt (=volts x amps) is always a watt , but an amp is only an amp at a specific voltage. Ever notice that the 13.5kv line that feeds your entire neighborhood is smaller than either of the 120v lines that feed your house? Same with a welder, the 12/10/8 guage power cord is much smaller than the welding leads. That's because your welding with 1/10th the voltage so a much bigger lead is necessary to carry the increased amps. Otherwisw how could you get 180 amps from a machine on a 40 amp breaker???
Wire charts assume the reader knows that the amperage numbers are all given for the same specific voltage. JJ's chart may be being presented out of context for a purpose. If this chart is for 12 volt automotive work it makes more sense. For example 30 amps x 12 volts =360 watts or .48 hp, whereas 30 amps x 120v =3600 watts or 4.8 hp. #6 wire x 20' will carry either load( according to that chart) but 3600 watts at 12 volts is 300 amps which #6 will not carry for very long...MikeD74T