Thoughts on Welding

[ajoeiam]

In the electrical design world, the rating of any given wire or cable depends on where you put it.
Cables suspended in free air have a much higher rating than the same cables installed in conduits.
Cables in ductbanks have to be derated depending on how many cables are around the.
Wiring installed on high ambient conditions are derated per a chart.

I had to install an exhaust fan on one large temporary feeder that was on the roof.

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You still haven't addressed the concept of a duty cycle for cables or wires - - - - which was my question.

I hadn't mentioned anything to do with capacity de-rate based on conditions which is quite a different thing.
(There is the concept of duty cycle on welding machines. The way this concept is used is, imo anyway,
quite different between Europe and North America. But that - - too was not what my question pertained too.)

 

[GreenTwin]

I have never heard of duty cycles on wires or cables.

For conductors in ductbanks, there are columns for percentage load I think.
If you know you will have a continuous load, such as lighting loads, you have to design the conductors, panelboards, etc. at 125%, else they will overheat.

You can get standard welding cables rated for 75C, 90C, and 105C, but as I mentioned, the limiting factor is the rating of the termination.
Most standard terminations are designed for 75C.
The termination can determine the maximum current rating.
Using a high temp rated conductor with a lower temperature rated termination limits the ampacity to the rating of the lower rated termination.

A typical 225A Lincoln tombstone welder has I think a 30% duty cycle.
Per Lincoln: Duty cycle is the percentage of a ten minute period that the power source can operate at a given output current level before exceeding its thermal limit (i.e. the windings get too hot) and shutting down if it has thermal overload protection.

I have always added on to my welding cables, since my welder is inside the shop, and I weld outside the shop in the driveway.
Adding to the cable length causes voltage drop, and so I generally upsize my cables at least one size when I lengthen them.

I live in a high ambient temperature zone, and high ambient temperature directly affects how much current a cable can handle safely.
You can push more current through a cable without overheating it if you are welding in a cold climate.

The stock cables on a tombstone Lincoln are pretty minimal, and you can bet they are designed to be no larger than needed for a 30% duty cycle.
I tend to pushy my welder pretty hard sometimes, and thus another good reason to use one or two sizes larger than stock tombstone cables, since I probably exceed the 30% duty cycle.
I do sometimes trip the breaker that feeds my welder on long-time overload if I weld too long at too high a heat.

A Lincoln tombstone says 225A, but in reality a maximum with a standard stick is more in the 100-150 range maximum.
The 225A rating is exaggerated in my opinion, and you won't weld very long at all with a tombstone at 225A without exceeding the duty cycle, and/or tripping the breaker feed the welder.

As far as in the US, to my knowledge, conductors have a given continuous current rating at a given ambient temperature, with a given insulation rating.
Any deviations such as with higher ambient temperature, or a lower termination such as 60C, reduces the cable rating accordingly.

The power company looks at load demand factors, but the NEC basically says you need to size bussing for 80% of the face value of the connected breakers, or if the entire load is continuous, size the bussing at 100%.

I normally don't exceed 60% loading on any conductor, because terminations get old, lose, and corroded, and feeders often go through the top of industrial buildings where the ambient temperature can be very high.
I never design for perfect conditions, and I never design to me Code required minimums.
I consider designing designing to Code minimums dangerous in many applications, since there is no room for error or equipment/connection/contact degredation.

Below is a welding cable sizing chart from Lincoln.

 

[GreenTwin]

Here is a welding cable ampacity chart from IEWC.
Text in italics/blue are from the chart.

Note that there are several variable that factor into the stated cable rating, such as:

1. Don't use the ratings for anything other than welding cables.
2. The total circuit length includes both welding and ground leads (based on 4-volt drop) 60% duty cycle.
3. These values for current-carrying capacity are based on a copper temperature of 60C (140F), an ambient temperature of 40C (104F), and yield load factor of approximately 32% from the 2 AWG cable, approximately 23% for the 3/0 AWG cable and higher for the smaller sizes.
4. In actually service, the load factor may be much higher than indicated without overheating the cable as the ambiet temperature will generally be substantially lower than 40C.


40C is 104F, and in this part of the country, we often have 110F days.
South of here can have higher temperatures than 110F, so the converse is also true for item 4, in that you may need to increase the size of your cables from that recommended in the chart if you live in the south USA.

If you are exceeding a 60% duty cycle (item 2), then you would also need to increase your cable size from what is shown in the chart.

The voltage drop is probably not too big of a concern, but you would not want to exceed about 5% maximum.

Copper and aluminum conductors have different current ratings for the same size cable.
Note that the chart below is for copper conductors only (item 3).

I would read item 3 as saying that cables based on the chart below could operate at 60C (140F),when the ambient is no more than 104F, and the cables need insulation rated at a higher temperature than 140F.
Typically cable charts give a maximum voltage rating for the cable, but I don't see that in this chart.

I don't know what the "yield load factor" is, so I will have to research that.

So again, I don't know of a duty cycle on conductors, but you do take duty cycle into consideration when sizing a welding cable.

Hope this helps clarify.


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[GreenTwin]

Here is another welding cable chart that deviates significantly from the one above, which I find rather unusual.

This chart is far more conservative with cable sizes, and I am not sure why.
I tend to size conductors conservatively, and so I would probably follow the chart below if I were setting up a commercial welding shop.
For home shop use, the chart above woud be sufficient.

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[GreenTwin]

The National Electric Code NEC article 630 covers circuits and overcurrent protection for welders or groups of welders, but says very little about welding cables.

There are other industry standards for welding cables, such as UL and SAE.

I still have not found a "yield load factor" as it would relate to a welding cable.

I found multiple cable current rating charts from multiple cable manufacturers, and they all use the same identical boilerplate language about "yield load factor".

So I have to guess this is driven by some Code and/or standard of manufacturing or testing.

I guess it could be a physical yield of the copper due to pulling on the cable?

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[Steamchick]

The weldercwho cooked cables was using a single power and single earth and the insulatiob rubber was smoking! Too hot to handle. He had thick padding onnhis dhouldef because of the heat so we doubled up and although heavy, the cables stayed cool. They melted the snow where they lay before we doubled up. Minus 12C.
It was common practice to double up earth cables on the aluminium MIG welders. They were joining busbars 6in x 30 in section. Doing a half- inch vee-butt welds 30in long in a single pass... not home/small workshop or garage welding.

 

[TimTaylor]

Steamchick - re: post #25

Good info. I agree that fuel tanks can be successfully welded with proper cleaning and purging to keep vapors below the LEL. For smaller tanks, you can additionally flood the interior with N2 gas at a couple inches WC to scavenge any O2 - this also helps reduce weld oxidation.

For thinner walled workpieces, 0.125" or less , I prefer to use TIG/Argon with an appropriate filler metal rod.

For thicker materials, I'll use MIG. CO2 shield gas is cheap, and works well for plain old carbon steel, but an argon/CO2 mix gives you more versatility for other metals.

 

[Steamchick]

Not having TIG, I braze or silver solder thin stuff. I have heated with both flame blow-torches and a carbon-arc torch - which is great when you get the hang of it. I'm just not sure if it gives off shorter wavelengths than UV though... Maybe nothing worse than metal arc welding I guess? You do need a really dark lens in the hood though.
K2

 

[Steamchick]

Any tank that has contained hydrocarbons can be classed as a fuel tank. e.g. Motorcycle oil tanks, hydraulic fluid containers, etc.
Water with detergent and steam work successfully for me, as I do not have inert gases to hand. And steam is hot so helps vaporise any soaked-in fluid (in the seams, rusty patches, cracks, etc.).
K2

 

[ajoeiam]

In the electrical design world, the rating of any given wire or cable depends on where you put it.
Cables suspended in free air have a much higher rating than the same cables installed in conduits.
Cables in ductbanks have to be derated depending on how many cables are around the.
Wiring installed on high ambient conditions are derated per a chart.

I had to install an exhaust fan on one large temporary feeder that was on the roof.

.

Hmmmmmmmmmmm - - - - still haven't seen anything related to a 'duty cycle rating' on cables.
I am quite aware of cable and wiring de-rate due to a large number of factors.

 

[ajoeiam]

Here is another welding cable chart that deviates significantly from the one above, which I find rather unusual.

This chart is far more conservative with cable sizes, and I am not sure why.
I tend to size conductors conservatively, and so I would probably follow the chart below if I were setting up a commercial welding shop.
For home shop use, the chart above woud be sufficient.

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View attachment 150178

Hmmmmmmmmm - - - you're making it sound like the recommendations from Lincoln Electric are inadequate for commercial use.
Point of fact - - - I've never seen even the big industrial fabrication sites even use any heavier welding cables - - - and if you think were were not very strictly controlled on every aspect of the process you would be dreaming.
This second table is an example of what I call hyper-conservatism - - - meaning - - - - well you're being conservative so to prove that I'm even more better (deliberate word choice to reflect . . . ) than you are I will be even more conservative than you are. The only entities that win such contests (imo often sponsored by regulatory agencies and/or their persons) are the suppliers - - - who are laughing all the way to the bank.

(There was a comment in an earlier message about duty cycle and welding cables - - - I have been pushing to see if there is such located anywhere. I think it is quite clear at this point that such information is quite 'vaporware'.)

 

[GreenTwin]

Yes, I have to guess that "duty cycle" for a welding cable is just someone's idea of how to not overheat a welding cable.
I have not found anything about it anywhere.

The more money that is at stake, and the bigger the industry, the more conservative they tend to be about everything, because saving a few dollars can cost them millions in minutes. One company that called me melted a 6,000 amp service entrance when they thought their conductors were sufficient (they were not), and it cost them $20,000,000.00 over a 4 day period. Other companies I have worked for can lose 20M in an hour if they get shut down.

I have worked with some big name worldwide companies, and believe me, they never ask for the cheapest method.
They want the most reliable method and materials, and what has the best long-term cost, not the best initial cost.

Any given setup of welding cables for industry is going to depend on their duty cycle and their ambient operating temperature, and so you cannot generalize about all companies doing this or that; that is just speculation.

There are some manufacturers who post conservative numbers in order make more profit, but I can tell you that 600 amps in a 100 foot #4/0 cable seems to really be pushing things, and you would have to look very closely at duty cycle, ambient temperature, termination ratings, etc if you go to that extreme.

A typical commercial/industrial #4/0 stranded copper THHN conductor in conduit is good for about 230 amps.

If you are in a position to design a welding installation as I have been (a long time ago I did a bicycle plant that had a welding operation), you have to accept liability for any failure of your design, so it never pays to design close to the failure limits; and no good design engineer does that because it is not a perfect world, and things happen.
Folks who don't have to stamp drawings and accept the huge liabilities that goes with stamping drawings tend to talk as if risk-taking is no big deal (no big deal to them anyway).
It can be a big deal, even if you just burn down your shop.
Do your homework and make your decisions wisely in any endeavor.

.

 

[L98fiero]

Steamchick - re: post #25

Good info. I agree that fuel tanks can be successfully welded with proper cleaning and purging to keep vapors below the LEL. For smaller tanks, you can additionally flood the interior with N2 gas at a couple inches WC to scavenge any O2 - this also helps reduce weld oxidation.

For thinner walled workpieces, 0.125" or less , I prefer to use TIG/Argon with an appropriate filler metal rod.

For thicker materials, I'll use MIG. CO2 shield gas is cheap, and works well for plain old carbon steel, but an argon/CO2 mix gives you more versatility for other metals.

FWIW, and not suggesting anyone else do it, but when I was younger and at least thought I knew more, I used to braze automotive fuel tanks. Granted, it's not welding but it has some relevance.

Where I lived had no paved roads so car fuel tanks were pretty beat up along the leading edge from stone impacts and cracks would form along sharp edges. At the time the recommendations were to flush multiple times with water or run the exhaust from an engine into the tank, neither seemed like a good idea.

The way I brazed the tank was to fill the tank to within a couple of inches of the crack and proceed to do the braze. The logic was that the heat would vaporize enough fuel to put it over the concentration where it would burn and the braze could be done safely. I probably brazed 50 tanks that way and I'm still here, none the worse for having done it, but to repeat the usual disclaimer, make no recommendation that anyone else try doing the same.

 

[GreenTwin]

The problem I have sometimes when trying to repair copper water lines around the house is that it can be tricky to get all the water drained out of the pipe, and so the residual water flashes to steam, and ruins the solder joint.

I would think a water-filled tank would have similar problems with the water boiling and coming out the joint as steam.

The inert gas filling sounds like it could work, if you happen to have some on hand.

My dad warned me about welding fuel tanks, 55 gal drums, etc.
He knew a guy that worked down the street who blew his arm off while welding an empty and "clean" 55 gal drum.

He may have been cutting it with a cutting torch, and could have filled it with unburned gas or something.

At any rate, use caution.
Spare arms are hard to find, and even harder to attach.

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