Scored a welder. Is it any good?

[Transit]

Prove / data and information, lists, tables and links
http://www.bnoack.com/index.html?http&&&www.bnoack.com/data/wire-resistance.html
Page AV-info, four pages down. Shows the maximum allowable current in conductors.
Other tables list the current that will produce a FAILURE of the conductor and that in fact is 40 amps for a # 12 wire. A 20-amp breaker gives you a safety factor of 2. With a 40-amp breaker, the safety factor is 0. Why would you want to limit the current to a level that will destroy the wire and cause a fire?

 

[jsborn]

"code says 40A needs a min of 8ga"

If you don't believe this then there is no use trying to explain it any further.

If I where you I would keep plenty of wieners and marshmallows on hand cause soon or later you will have a fire.

The code was written by a lot of very smart people using sound engneering principles and a lot of testing and whether you believe it or not it has served well. So keep running you welder on 12 ga wire and one day you will load it up or the welder will short out (which is another part of the subject we have not even discussed ...Fault current ..) and your 40 amp breaker will not trip until the wire has melted and then its too late.


Good luck to you

 

[Transit]

"code says 40A needs a min of 8ga"

If you don't believe this then there is no use trying to explain it any further.

If I where you I would keep plenty of wieners and marshmallows on hand cause soon or later you will have a fire.

The code was written by a lot of very smart people using sound engneering principles and a lot of testing and whether you believe it or not it has served well. So keep running you welder on 12 ga wire and one day you will load it up or the welder will short out (which is another part of the subject we have not even discussed ...Fault current ..) and your 40 amp breaker will not trip until the wire has melted and then its too late.


Good luck to you

I got the same info from the site I listed. BTW, most of the NEC is written by Fire Marshals and insurance companies. Why is that?

 

[Brad_Blazer]

LOL
P=IV
V=IR
=>P=I*I*R
The rate of heat generation by resistance equals current squared times resistance. That's why they call them "I squared R" losses. Voltage is not a factor but duty cycle and thermal resistance are factors.

 

[LD1]

I think I found the formula for voltage drop so someone correct me if this is inaccurate

Vd=KID/CSA
K=resistivity factor........7 for Cu and 11 for ALU
I=amps
D=round trip length
CSA=cross section is circular mils

For a 12ga 30ft power cord on 40amp 240v circuit

7 x 40 x 60/6530(csa of 12ga)
16800/6530=2.57volt drop

2.57/240=1.07%

So is volt drop an acceptable way to size wires???

And if not, WHY??
And why do all the online calculators like use it to size wires??

According to this one, a 12ga wire @30ft and 240v would be good up to 60amps and still be under the 3%
Wire Size Calculator

They even say on their website "Our calculator yields results that are within code in most locations " and "Since we have tried to consider safety as our primary factor, any marginal decision factors are toward the safe side. We allow a maximum voltage drop of about 3% before the wire specification increase"

Are you guys saying that the information this calculator is giving is unsafe, and if so, WHY?

 

[gpflepsen]

LD1, look at the voltage drop for the "round trip" of the wires that make up the total conductor.

In this context i'm calling the conductor the bundle that is delivering the power; it consist of two current carrying wires, insulation, and more insulation.

Each wire is having just under 3% voltage loss. Combine these two wires in the conductor and you are looking at just under 6% voltage loss. Remember, voltage loss = heat generation which is what the whole fuss is about.

You may be quoting calculators that are assuming one wire, free or in a conduit. Your application is wires bundled into a conductor. Do you see this difference? The calculator is giving safe conditions for a heat generation rate of a wire. You are using a conductor with 2x the heat generation rate. The NEC, in part, derates current capability to accound for this.

 

[LD1]

LD1, look at the voltage drop for the "round trip" of the wires that make up the total conductor.

In this context i'm calling the conductor the bundle that is delivering the power; it consist of two current carrying wires, insulation, and more insulation.

Each wire is having just under 3% voltage loss. Combine these two wires in the conductor and you are looking at just under 6% voltage loss. Remember, voltage loss = heat generation which is what the whole fuss is about.

You may be quoting calculators that are assuming one wire, free or in a conduit. Your application is wires bundled into a conductor. Do you see this difference? The calculator is giving safe conditions for a heat generation rate of a wire. You are using a conductor with 2x the heat generation rate. The NEC, in part, derates current capability to accound for this.

The formula I quoted first for total round trip length of the circuit, that is why I used 60ft even though I only have 30ft of cord.

The online calculators are asking for 1/2 the total length so I plugged in 30ft. Is this incorrect??

I assumed that on the calculator when you check 240v single phase like we have in the US, that it would factor two power wires to carry the load.

 

[moeh1]

Brad got most of Ohm's formulas above. The remaining one is that Power is also equal to the volatge squared divided by the resistance. Voltage most definitely has a place here and it relates to resistance heating of the wires as the current goes thru it. The NEC looks at wire, types of insulation, resistance, residential and commercial wiring practices (conduit romex etc.) and publishes a set of generally accpeted safe practices that have been time tested and improved after learning from failure. I am not disparging any other Java calculator on any website, but I would use the codebook for residential work - the wire may hold up but something else might burn. Automotive etc, with individual wires and lower voltage are able to carry higher current that their residential counterparts.

 

[Danno1]

So far I have come up with these factors that affect wire size
1.Amps
2.Volts
3.Length of run

Other factors:

4. conductor material (Cu, Al, being the most common)
5. single wire in air (your alternator wire) or bundled (AC in a conduit)
6. Regulatory Agency (Mil-W-5088, NEC, UL/CSA, TUV, CE, AIA, FMVSS, etc)


There are others but this is what comes to mind at the moment.

.

 

[Danno1]

But, the question I have never got a straight answer to is why wires are rated in amperage and not watts??? Maybe theres an electrical engineer on here who could help us out.

It is my understanding of electricity that watts are what does the work/creates the heat. Wires are rated on how much current they can carry without getting to hot. Heat being the limiting factor. They have to stay under a certain temp to keep the insulation intact. Watts are what creates the heat. More watts =more heat.

Yes, the power does the work/creates the heat; and yes, more watts = more heat.

Where you are confused is the diff bet the power being dissipated at the load and the power being dissiapted in the wire itself.

The power at the load is xxxVAC times xxxAmps = P_load
The heating of the wire is caused by the 1-5% voltage drop times xxxAmps = P_wire

.

 

[gpflepsen]

LD1, take that java calculator you used. Put in a 1A load on a 50' extension cord. What do you get?

I don't trust the results. They are very overly conservative. I think in your specific examples, they are under conservative.

I use a 30' SOOW 10/3 extension on my welder. It uses 28A at 230V rated output. I have no worries.

My vacuum has a 30' 17AWG for 12.5A. It gets warm with use. I don't like that. It should have a 14AWG cord, but it is intermittent use. It's UL listed, go figure.

The Mrs. likes to use those 1500W heaters in the winter. I ***** about it because... they draw over 12 amps and some have 16AWG cords. They get warm and the circuirt breakers are probably 15A on the outlets she uses. Technically it gets the job done, but I don't like it. I guess we're OK because the insulation is rated for 105ｰC.

Go to TSC 12/3 Extension Cord and tell me what you would do if you had a 15A load 100' away? Plug the 1500W heater in an see how the package performs. Better yet, plug in a 1 1/2 HP saw in and see how it likes it!

In the end, you can use whatever cords you want, and you may be reducing the margin of safe operation. I think a 12AWG cord is decreasing the safety margin. Check out the following: Portable power cord cable SO 10 5 SOOW 12 4 16 3 10 2 . They have a decent lineup and "suggested" amp capacities.

 

[BigEddy]

LD1.
Think of electricity as water.
Think of voltage as pressure.
Think of current as volume or flow rate (gpm).

A 600V cable vs a 48V cable is like a 1/2" hydraulic hose versus a 1/2" garden hose. One can withstand more pressure (voltage) than the other before it leaks (read shocks you) but both can carry the same flow rate (gpm or amps) as the other.

A #4 cable versus a #14 cable is like a 2" hose versus a 1/2" hose. One provides a lot less resistance than the other. At low flow rates (low current) they both work just as well, but as the flow rate increases, there is more resistance to flow in the small hose than the large one - therefore some of the pressure (voltage) is lost travelling through the hose - that loss being in the form of heat, which further increases the resistance increasing the loss even more. That drop in voltage at the outlet also means more current has to flow to your tool / welder to accomplish the same work. It spirals.

I'm sure you can understand how more length also increases the amount of pressure lost (=heat generated = voltage drop) during transmission, hence why #14 may be okay up to xx', but #12 is required for longer runs.

Electrical code takes into account these factors, plus cooling factors (free air versus shielded), differences between AC and DC applications (we will skip eddy currents and so forth for now), solid versus stranded, as well as a number of other things, adds an appropriate safety factor to it, and determines a safe size of wire for each application. NEC also has a special section for welders where it takes into account the sporadic nature of the process and allows a smaller wire to be used - although a wise electrician will use the larger wire size any way.

Interestingly not all electrical authorities use the same rules. Here in Canada - #14 wiring is fused at 15amps for household use, I believe in the US it's 20amps.

Point of the matter is - use the right wire for the application, if in doubt - consult an electrician or someone familiar with the code. No one on here is going to use a garden hose as a poor mans substitute for a hydraulic hose (I hope!!) so why would one use the wrong wire to hook up their welder?

 

[gpflepsen]

Interestingly not all electrical authorities use the same rules. Here in Canada - #14 wiring is fused at 15amps for household use, I believe in the US it's 20amps.

US = 15A breaker for 14ga wire, 20A breaker for 12ga wire.

 

[LD1]

LD1.
Think of electricity as water.
Think of voltage as pressure.
Think of current as volume or flow rate (gpm).

A 600V cable vs a 48V cable is like a 1/2" hydraulic hose versus a 1/2" garden hose. One can withstand more pressure (voltage) than the other before it leaks (read shocks you) but both can carry the same flow rate (gpm or amps) as the other.

I was wondering when someone was going to use the good ole water analogy

Quite simply the flow rate isn't going to be the same. a 1/2" ID garden hose @50psi is going flow a lot less than 1/2" ID Hyd Hose @ 3000psi

For this reason is why I have never liked the water analogy. Everyone compairs amps to flow, but with water, increase the pressure, you increase the flow. with electric, if you increase the volts, the watts go up, ant not the amps.

 

[LD1]

LD1, take that java calculator you used. Put in a 1A load on a 50' extension cord. What do you get?

I did that and it said 14ga. I also lowered it to .001amp and 1ft and it still said 14ga. So I have come to the conclusion that that particular calculator doesn't go smaller than 14ga

Other factors:

4. conductor material (Cu, Al, being the most common)
5. single wire in air (your alternator wire) or bundled (AC in a conduit)
6. Regulatory Agency (Mil-W-5088, NEC, UL/CSA, TUV, CE, AIA, FMVSS, etc)


There are others but this is what comes to mind at the moment.

I did mention those things except the regulatory agency.

For the sake of argument, pretend their is no regulatory agency. Because what I am trying to do is understand the science and math behind the reccomendations they make, and not just because "We are the big bad NEC, or whatever, and because We said so"

 

[gpflepsen]

For this reason is why I have never liked the water analogy. Everyone compairs amps to flow, but with water, increase the pressure, you increase the flow. with electric, if you increase the volts, the watts go up, ant not the amps.

The two act exactly the same. If you increase the voltage, the current and power go up. The flow will find it's balance with the given source of effort (pressure or voltage) and the resistance seen.

 

[bobodu]

I sure as **** wouldn't run anything smaller than 8 ga. for more than two feet......

 

[BrentD]

I was wondering when someone was going to use the good ole water analogy

Quite simply the flow rate isn't going to be the same. a 1/2" ID garden hose @50psi is going flow a lot less than 1/2" ID Hyd Hose @ 3000psi

For this reason is why I have never liked the water analogy. Everyone compairs amps to flow, but with water, increase the pressure, you increase the flow. with electric, if you increase the volts, the watts go up, ant not the amps.

You're confusing a few things here... There is a difference between the current carrying capacity of a wire and the power used by a tool. "Watts" as a measure is typically used to determine how much "power" is required to do a certain task such as spin a wheel, light a filament, heat coffee, etc.

In other words, "Watts" is typically used in reference to loads or generating capacity. Let's say you have an electric motor that has wiring terminals for either 220V or 110V and a power rating of 1hp. (1hp = ~746W) If you have the motor wired up for 110V it's going to be pulling about 6.8 amps. But if you switch it over to the 220V wiring, it's only going to be pulling 3.4 amps. Either way it's still a 1hp motor and it's still using 746 watts. Granted, these are ideal numbers that would be larger in the real world due to inductive losses, etc but it gives a good example of why Watts don't necessarily increase with voltage. If you hooked those 110V windings up to the 220V supply the motor would still draw close to the 6.8 amps that it did on 110V but it would also be spinning twice as fast or producing twice as much torque, at least until the windings overheated and the whole thing melted.

As for breakers, that's simply a matter of how the ratings are calculated. In a normal single-phase 220V system in the US, you have 3 wires. 2 Hot wires and a "neutral" wire. 110V breakers are rated for a circuit flowing from 1 hot wire to 1 Neutral. 220V breakers, on the other hand, are rated for the total current flowing through it's internal contacts between the two hot wires.

If you used a 220V 20 amp breaker to power 2 110V loads with power flowing from the breaker through the load to neutral then yes, you could have 20 amps on each leg because 20 amps is all that would be flowing through the contact for that leg. But if you're running a 220V breaker, then you're measuring current leg to leg and a 20 amp 220V load is causing a 20A flow through "BOTH" contacts. If you want to visualize it as DC you can think of it as flowing out one contact, through the load and then back through the other breaker contact to the other leg, where the 110V load would only be out one contact through the load then on to the neutral wire.

 

[patrick_g]

I have been told before that you could use 2 20amp breakers to make 40amp 220, as long as you connect the switches, so they trip together and you dont single-phase whatever your hooked to with 110v power.

You were told very wrong!

A 40 amp circuit uses a "twin" 40 amp breakers. You can substitute a pair of 40 amp single pole breakers and connect the levers together so that an overload on either leg will trip both breakers.

Pat.

 

[patrick_g]

My truck has a 130amp alternator and is connected to the battery with a 6ga wire and I can drive all day long and the wire doesn't melt.

It is very unlikely that your alternator puts out anywhere near 130 amps for more than a small fraction of "all day long."

If you put on enough driving lights and such you may be able to pull enough current for long enough time to experience melting the insulation off your alternator leads. Alternatively yo may be able to melt down the alternator.

Think duty cycle. I crank the engine of my diesel truck. I have two each 100 AH batteries in parallel. They supply oodles of amps from the battery to the starter (briefly.) Then after the engine starts the alternator supplies many amps to the battery but on a declining curve as the battery recharges. In a very few minutes the alternator output is quite low unless I am running lots of lights and stuff.

Pat