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

.