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...