LD1
Epic Contributor
When they run the power through the transformer the voltage goes way up, but the amperage goes way down, the total wattage is still the same.
As far as the breakers go, I have not heard that, but I will look into it.
Scored a welder. Is it any good?
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When they run the power through the transformer the voltage goes way up, but the amperage goes way down, the total wattage is still the same.
As far as the breakers go, I have not heard that, but I will look into it.
aczlan
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True, but the point is that the higher the voltage is the smaller the wire needed to do the same work.
That is why a car starter needs a large cable to do what you could do with a 30 amp 120v circuit running over a 10ga wire.
When you have a 240 volt circuit (note I am speaking of the US system, it is different elsewhere) you have two 120v lines which, if compared to ground you would find that one is at +120v and one is at -120v, they switch which is which 60 times/second (which is why the US grid is known as a 60 hertz grid). The voltage between them measures 240 volts.
Aaron Z
I was with you jack and then you went into the ditch. The current in the two-pole circuit breaker leaves one pole of the breaker and enters the other pole to complete the circuit. There is no 50-50 split or any other such voodoo.
Example: 120 volt @ 15 amps, single phase, # 14-ga wire, one pole breaker.
120 x 15 = 1,800 watts. Maximum power attainable.
With a 4% voltage loss # 14-ga wire at 25-foot max length.
120 x .94 x 15 = 1,692 watts
# 10-ga wire will have the same loss at 50 feet.
Same problem; 240 volts @ 15 amps, single phase, two-pole breaker.
240 x 15 = 3,600 watts. Maximum power attainable.
With a 4% voltage loss # 14-ga wire at 50-foot max length.
240 x .94 x 15 = 3384 watts
# 10-ga wire will have the same loss at 75 feet.
You can see that doubling the voltage will double the power for the same wire gauge and increase the circuit distance.
There are other NEC tables taking other conditions into account such as insulation temperature range and operating temperatures.
jsborn
Gold Member
Its not Voodoo I will try to restate what i said ..IF you take a load of X and a Voltage of 120v then you have a current of Z. If you raise the voltage to 240v for the same load X the current will not be exactly Z/2.
if you really want to muddy the water you are correct that on a 240 system the current leaves one pole of the breaker and returns on the other one but not at the same time since one pole it one the neg side of 0 while the other is on the pos side 60 times a second the current is actually 0 on both poles.
I think the reason there is so much confusion about comparing automotive and household current is prob due to the duty cycle. Not to mention the fact that one is AC and the other is
dc. Household currents are given and designed for more of a 100% cycle and automotive loads are normally of a shorter duration. While a Car Battery is able to supply hundreds of amps under normal conditions it will be delivering that current for only seconds as opposed to all day or hours at a time therefore a smaller wire can be used. I will guarantee you if you short out your # 8 battery cable to ground and hold it there it will melt
One thing I am very sure of though is if you put 100 amps on a conductor that is rated at 50 amps it will melt no matter what the voltage is.
LD1
Epic Contributor
I understand the voltage of a 240v system but the amps and breaker is what I have a hard time understanding.
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.
LD1
Epic Contributor
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. Same 6ga wire is only rated for 50 of 60 amps @600v. This is why I am saying that there is more to it than amps.
I think we were onto it with the voltage drop. The NEC codes for MAX amperage and the standards that everbody referes to (12ga-20amp/10ga-30amp/8ga/40amp, and so on), what length of run are they figured at. Most auto wiring, like batter-alternator-starter wiring is 8-10ft max. Most 120v+ applications are 100+ft.
jsborn
Gold Member
you can make a 20 amp 230 volt breaker with 2 20 amp 120 volt and a common trip bar. But if you need a 40 amp 230v breaker using 2 20's wont work it just don't add up that way no matter how much you want it to.
aczlan
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Wow, what a response. Sounds like a lot of ways that hooking up a welder have been tried. I talked to the electrician and work and here's what I plan. 8 guage wire to the recepticle. This will be dedicated to a 40 amp breaker. That should handle about all this welder can throw out. That leaves taking care of times that I have to work on equipment that I can't move close enough to the welder. If the welder works good then I'll just get extra long leads. I remember seeing a Lincoln 225 with 100 foot leads so I figure that'll work. Now if I can score a plasma cutter!!
LD1
Epic Contributor
Exactally my point. That there is more to it than just plain old amps.
So far I have come up with these factors that affect wire size
1.Amps
2.Volts
3.Length of run
The two wire size calculators that I found on google, one of which I posted earlier, these are the three main things they ask. As well as 1 or 3 phase and copper if aluminum wire.
So I think I have pretty much come to the conclusion that the most accurate way to size the wire is base off the voltage drop. As that is what the online calculators are doing.
I know there is a lot more to it, such as solid vs stranded, open air vs raceway, # of wires in raceway of conduit. All of these pertain to how hot the wire will get. And obviouslly the hotter, the less current it can carry.
As far as my 240v welder on a 40A breaker with 30 ft of 12ga soow, i have yet to find anything that says it is too small, except the people on here. So if anyone has any formulas or proof that it is dangerous, enlighten me. And I don't mean "code says 40A needs a min of 8ga" or whatever. Show me formulas. Voltage drop, temp of wire carrying said current, etc.
Again I am not being argumentative or hostile, i just want some real #'s and some real reasoning. And not just the same old standards that we are all used to. 14ga/15a 12ga20a 10ga30a yadayadayada. I already know that. I'm just trying to learn some reasoning behind it with some actual formulas or #'s