Scored a welder. Is it any good?
- Thread starter Marada
- Start date
- Views: 24803
patrick_g
Elite Member
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.
++++++++++++++++++++++++++
Because watts delivered to the load do not only depend on the ampacity of the wire. The wire has a few ratings of interest to this discussion.
1. highest allowed voltage for the insulation to remain safe at the highest rated temperature.
2. staying within the limit in #1 above amps is what counts in sizing wire and only derivatively does watts delivered matter.
First the equations needed to make sense out of simple electrical stuff:
I = E / R ___ where:
I = current in amps,
E = electromotive force in Volts, and
R = resistance in ohms
P = I * E Power in watts is equal to the current in amps times the voltage.
Example: If you were to use 600 volts to power a circuit wired with a wire safely able to carry up to 40 amps you could deliver up to 24,000 watts.
Using the same wire with 12 volts you could safely deliver up to 480 watts.
The folks making and the folks selling the wire have no clue what voltage you will use. It makes sense that they tell you the amp capacity of the wire.
+++++++++++++++++++++++++++++++++++++
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.
+++++++++
That is totally correct
++++++++++++++
The widely used amperage ratings of common wire sizes kinda assume a set voltage.
+++++++++++++
No, not at all.
+++++++++++
Lower the voltage and it should be able to carry more amps right?? Given the automotive 12v systems as an example.
+++++++++++++++
Absobloominglutely NOT RIGHT!!!
+++++++++++++++
And as far as having 2 hot wires on 220v to "share the load" not being an acceptabe argument puzzles me too.
+++++++++++++++++++++++++
In a 220/240 VAC circuit all the current flows in both wires in series. The chief difference is that a 240 volt circuit with a given size wire will deliver twice the watts of the same wire running 120 VAC.
The two wires do NOT SHARE the load such that each handles 1/2 the current. They both carry all the current. In a 120VAC circuit all the current passes through the hot wire AND the neutral in series. IN a 240VAC circuit the same thing happens. The wires are in series NOT PARALLEL!!
+++++++++++++++++++++++++++++
Again, I'm not trying to be argumentative or unsafe, I just don't understand the logic of the code. If someone could shed a little light on it for me please am all ears.
BTW My powercord for the welder is not tucked behind any walls, and I don't feel the least bit unsafe running my welder to max with it's 12ga powercord plugged into a 40amp breaker. Call me crazy
I know a guy who walked across the street without looking either way. He did it several times and was not killed or injured. Does that constitute a safe practice? Because you haven't burned up the wire or your house yet doesn't make it a good idea to get others to try.
P.S. I'm not a degreed electrical engineer nor did I play one on TV and I didn't stay in a hotel or motel room, recently. My last job title was scientist but now I run a small cow calf operation on my 160 acres. (14 momma cows, a bull and 9 calves and counting) OK I confess I have in the past, (but only for a few years) made a living as an electronics design engineer.
Pat
LD1
Epic Contributor
If a 14ga wire is rated for 15amps at ANY voltage why is it rated for 40amps in a 12V system????
The more I research this the more i think I am starting to understand.
Transit: according to my calculations, 240v system with 12ga wire and 40 amps 30ft length = 4.6 volt drop. Which is only 1.9% and is well under the 3% and 5% standards that I have been reading about, so why would the insurance company have a problem with me being under the 2% that you mention????
Like I said, I don't completely understand it., but I have found two calculators online (just google wire size calculator) and entered 30ft @ 40amps and 220/240v and both have said 12ga minimum.
I know what the code says and I know what the standard is for given amperage. All I am saying is that there has got to be more to it than just amerage.
You guys are telling me that it is unsafe and my insurance company better not find out yet I have found two calculators that says it's fine, I am only at 1.9% voltage drop, and I know from experience that it works and the wire does not get hot. So why does the standard say for 40amp that I need at least 8ga wire. What am I missing? There has got to be more to it.
The more I research this the more i think I am starting to understand.
Transit: according to my calculations, 240v system with 12ga wire and 40 amps 30ft length = 4.6 volt drop. Which is only 1.9% and is well under the 3% and 5% standards that I have been reading about, so why would the insurance company have a problem with me being under the 2% that you mention????
Like I said, I don't completely understand it., but I have found two calculators online (just google wire size calculator) and entered 30ft @ 40amps and 220/240v and both have said 12ga minimum.
I know what the code says and I know what the standard is for given amperage. All I am saying is that there has got to be more to it than just amerage.
You guys are telling me that it is unsafe and my insurance company better not find out yet I have found two calculators that says it's fine, I am only at 1.9% voltage drop, and I know from experience that it works and the wire does not get hot. So why does the standard say for 40amp that I need at least 8ga wire. What am I missing? There has got to be more to it.
patrick_g
Elite Member
It is good that you are researching the issue. There are a number of peripheral issues such as type of conduit, if any, enclosing the wires, how many strands in the conduit, and on and on.
It is not surprising that you may have found conflicting information on the internet. It certainly would not be the first time. Context of each reference is important as well as the source of the information. Not every source is of equal stature.
Pat
LD1
Epic Contributor
How is this true when "according to code" it would require a 8ga wire for the 600v/40amp application, when an 8ga wire is rated for 150amp in an automotive application.
jsborn
Gold Member
14 ga wire could be rated for many different amperages depending on type of use. example in conduit is less than in air which is less than in free air (outside like on a pole). It is based on a lot of factors none of which Can be omitted thus the need of charts and specs. Just to muddy the water more there are different ratings based on allowable temperature rise of the wire.
Just keep in mind if you use a breaker bigger in amperage than the wire can safely carry as per the NEC regardless of the voltage you will eventually have a fire and you will not be insured if the fire Marshall finds it.
patrick_g
Elite Member
LD1 I said nothing about code, automotive design standards, or anything resembling those two things.
What I said is a simple fact that is true. Neither of us may choose to use the same wire for both applications but so what? I was giving an example that was supposed to make something clearer for someone who wanted to understand, not quibble.
I could have chosen #2 welding lead as the wire in the example and the comparison would still be clear, concise, correct and communicative. This is true even though that neither of us might choose #2 welding cable for either application. It was an EXAMPLE not a how to for any specific wiring task.
Pat
What I said is a simple fact that is true. Neither of us may choose to use the same wire for both applications but so what? I was giving an example that was supposed to make something clearer for someone who wanted to understand, not quibble.
I could have chosen #2 welding lead as the wire in the example and the comparison would still be clear, concise, correct and communicative. This is true even though that neither of us might choose #2 welding cable for either application. It was an EXAMPLE not a how to for any specific wiring task.
Pat
LD1
Epic Contributor
I did not say you mentioned anything about code. But you said "safley handle the load" which is where I went to the code for my example.
I am not trying to quibble either, just understand.
But the part where you said that 14ga wire is rated for 15 amps at "any" voltage is what I was disagreeing with, because it simply isnt true. And that is where the 12v auto example came in at.
If there is a difference in allowable ampacities between 12v and 120v, why is their no difference between 120v and 600v?????
I am no electrical engineer, but I do understand the basics of electricity which everyone is quoting. I understand ohms law, watts law, voltage drop, # of wires in a raceway, open air, temp rise, and all that good stuff.
What I don't understand is how amperage is the only way wires are measured for capacity. If that were the case, a 1000amp auto battery would require a wire about the diameter of a golfball.
aczlan
Good Morning
- Joined
- Mar 7, 2008
- Messages
- 16,985
- Tractor
- Kubota L3830GST, B7500HST, BX2660. Formerly: Case 480F LL, David Brown 880UE
In the US a 40 amp 240v circuit has two 40 amp legs, not two 20 amp legs, if you look at 40 amp 240v breakers, they are (often) a pair of 40 amp 120v breakers permanently connected to each other.
True, but at higher voltages the required wiresize is smaller, that is why they run transmission lines at such high voltages (.5 megavolts IIRC)
Aaron Z
