Yes, please - some clarification is needed here. I'm a bit confused.
Yes, please - some clarification is needed here. I'm a bit confused.
OK, I have to apologize for any confusion I may have caused with my previous comments. I just had it explained to me by a friend who's more well-versed in physics than me:
Basically, I was confusing input and output when it comes to power being produced. A cutter operating at 120V requires more amperage to produce a given wattage than the same cutter operating at 240V. For example, let's say 3600 watts are needed to complete the cutting operation. At 120V, that would mean 30 amps of draw from the outlet (3600/120), whereas at 240V the draw would only be 15 amps (3600/240). So a 20-amp breaker would trip if the voltage was 120, but it probably would not if the line was 240V. At least, that's how I'm understanding it now...
Basically, I was confusing input and output when it comes to power being produced. A cutter operating at 120V requires more amperage to produce a given wattage than the same cutter operating at 240V. For example, let's say 3600 watts are needed to complete the cutting operation. At 120V, that would mean 30 amps of draw from the outlet (3600/120), whereas at 240V the draw would only be 15 amps (3600/240). So a 20-amp breaker would trip if the voltage was 120, but it probably would not if the line was 240V. At least, that's how I'm understanding it now...
Also Amps is the pressure in the water hose example, not volts if memory serves me right.
Also the reason that a 12v battery does not harm a person is not really the current size, it is more related to what is called Potential effect. Basically the 12v system does not have enough potential energy to electrocute a person. I dont remember from class where it starts but I think it is around 25v or so that the Potential is over come. This is the same principal that is used in how high voltage electricians (lineman) are able to touch the lines without being electrocuted. They are at the same potential as the lines (same voltage). It is when they are grounded and standing on the ground that they are a lessor voltage and able to be electrocuted. Then you start getting into Step Potential as well.
Ohms law is I=V/R
I is Amps
V is Volts
R is resistance (ohms)
Amps is found by dividing volts by resistance, resistance is found by dividing volts by amps, volts is found by multiplying resistnace by amps.
The is also the Power formula as well.
P= I/E
P is Watts
I is Amps
E is Energy or Voltage
To find out how many watts something is using you take I * E to get Watts.
Also the reason that a 12v battery does not harm a person is not really the current size, it is more related to what is called Potential effect. Basically the 12v system does not have enough potential energy to electrocute a person. I dont remember from class where it starts but I think it is around 25v or so that the Potential is over come. This is the same principal that is used in how high voltage electricians (lineman) are able to touch the lines without being electrocuted. They are at the same potential as the lines (same voltage). It is when they are grounded and standing on the ground that they are a lessor voltage and able to be electrocuted. Then you start getting into Step Potential as well.
Ohms law is I=V/R
I is Amps
V is Volts
R is resistance (ohms)
Amps is found by dividing volts by resistance, resistance is found by dividing volts by amps, volts is found by multiplying resistnace by amps.
The is also the Power formula as well.
P= I/E
P is Watts
I is Amps
E is Energy or Voltage
To find out how many watts something is using you take I * E to get Watts.
Sorry but your memory isn't.. Your formulas are correct and can be easily found but everything else is just wrong.. The reason a 12 volt battery won't shock you is because 12 volts isn't enough voltage to overcome the resistance of your body.
In other words.. 12 volts isn't enough pressure to push enough current through the high resistance of your body to hurt you.
This is a pretty good analogy and gets used often. Just remember, electricity can not be exactly related to anything but lets elaborate just a little. Remember for our example..
Volts - pressure
Amps - volume of water moved in pipe
Watts- Amount of water consumed over a period of time ( an hour)
Imagine the OP's plasma cutter but instead of using electricity to run it uses water (I said imagine). Ultimately, it needs a certain amount of water to do its job even though It was built to self adjust to handle 2 input pressures (voltages).
Still following? Note the bold.. Built to handle..... so dont get smart and try to send 240volts to your shop fan or anything not rated for it.
OK... At a pressure of 120v it takes a pipe that is twice as big as it would need to be if the pressure was doubled (or 240V) to deliver enough water to feed the machine. Does that make sense? Its two ways to ultimately fill a bucket of water at the same rate.
The benefit of higher voltage is being able to use a smaller pipe (wire) to move the same amount of electricity.
I'm going to go out on a limb and assume that the OP has a "CUT40" plasma cutter. I looked up the specs on one and the MFG list that the unit consumes 4.5KW of electricity at full load (4,500 watts ). WOW! So if we use OHM's law. 4500watts/120V = 37.5 amps -----
OR
4500watts/240v = 18.75 amps
as a rule of thumb, a breaker is only good for 80 percent of its rated capacity for continuous use ( a 20 amp breaker is good for 16 amps) so even if the machine is turned down to a half load of 18.75 Amps you are still going to trip the breaker.
OKAY now that we are totally confused.
The reason why a 12volt battery poses no imminent threat to a human is that our bodies have a certain level of resistance to its pressure (voltage) Just like a water hose can be stopped up by plugging it up with your thumb a human body generally can resist 50 volts (FACTORS AND INDIVIDUAL CHEMICAL MAKEUP CAN & WILL CHANGE THIS VALUE) So voltage is what makes electricity dangerous. Now with that said and without elaborating until the cows come home... Current is what actually kills. If My memory serves me well.... The minimum level of current determined to be death via electrocution is 50ma or .05amps. This is enough current to stop your heart but it MUST overcome the resistance of your skin.
NOW for my disclaimer. The content above is not cited and is given with the express use that the reader takes the information and use it at their own risk. no guarantee expressed or implied. The above was written to give an insight to how electricity works not the exact science of it
Thanks for the elaboration! I had been looking at the problem from the wrong angle, but now that I've got the right perspective in mind, I can see how Ohm's Law and 120V vs. 240V work out. Also, the cutter in question is a Thermal Dynamics Cutmaster 38, which at full load consumes 3220 watts. That's 26.8 amps at 120V, so with continuous use at partial load, the cutter could still trip a 20-amp breaker. Makes sense, because I can run the cutter for 10-12 seconds before the breaker trips. So an upgrade is in the works (of course, done by a professional!)
And to confuse things even more positive and negative terminals indicate hole flow not electron flow.
Sorry if my explanation is hard to read. I wouldn't make a good tech writer.
Another neat little tidbit of information of anyone cares to know....
There are lots of different kinds of breakers the most common of which is the thermal magnetic type ( and there are sub-kinds of them also). It does not see a pre-determined level of current and then trips like some people think. As current flows through an element inside heats up in respectively. More current makes more heat where it eventually trips the circuit ( opens the circuit). The reason for this is because a lot of things (mainly with motors). Motors pull many times their rated current in the instant they start. Thermal trip (HACR Rated specifically) breakers factor start-up into their operation. When I was doing service for computer rooms some clients required up to test breakers before we used them. We had engineers draw us up a spec that included calculating the trip time ( min and max). many people would be surprised to learn that most modern 20 amp breakers on average can hold ( and more importantly interrupt) over 600 amps for just a couple of seconds.
Also, Poor connections among other undesirable things produce heat. so, A poorly connected breaker in a hot shop wouldn't act the same as one properly installed in a conditioned space
Now for a little rant if you'll humor me. Since we are talking about breakers I'd like to express my dislike of Federal Pacific breakers that are no longer made ( Zinsco are not much better) A joke in the industry is that you can (and I have actually seen people do it) weld directly off of one. They simply do not work. A friend of mine hired a contractor to remodel their kitchen and install an under counter electric range in addition to the other one they had. The contractor Did not have room in the panel so he double tapped 2 single pole 20a breakers...... One of the 20's fed recepts that were commonly used to vacuum the house ( about 14 amps for a good vacuum and The range pulled 40 amps with both elements on ) They used it that way for years and when they did they always smelled a foul odor. Come to find out the odor was the oil in the Bakelite recepts and romex in the walls cooking off. Poor install into a poor system almost burned down the entire house.....
Disclaimer again. The content above is not cited and is given with the express use that the reader takes the information and use it at their own risk. no guarantee expressed or implied. The above was written to give an insight to how electricity works not the exact science of it
ETA: Here are some cool youtube videos
http://www.youtube.com/watch?v=uMV1jmDn3o4
http://www.youtube.com/watch?v=MkVMCAPnKGY
Another neat little tidbit of information of anyone cares to know....
There are lots of different kinds of breakers the most common of which is the thermal magnetic type ( and there are sub-kinds of them also). It does not see a pre-determined level of current and then trips like some people think. As current flows through an element inside heats up in respectively. More current makes more heat where it eventually trips the circuit ( opens the circuit). The reason for this is because a lot of things (mainly with motors). Motors pull many times their rated current in the instant they start. Thermal trip (HACR Rated specifically) breakers factor start-up into their operation. When I was doing service for computer rooms some clients required up to test breakers before we used them. We had engineers draw us up a spec that included calculating the trip time ( min and max). many people would be surprised to learn that most modern 20 amp breakers on average can hold ( and more importantly interrupt) over 600 amps for just a couple of seconds.
Also, Poor connections among other undesirable things produce heat. so, A poorly connected breaker in a hot shop wouldn't act the same as one properly installed in a conditioned space
Now for a little rant if you'll humor me. Since we are talking about breakers I'd like to express my dislike of Federal Pacific breakers that are no longer made ( Zinsco are not much better) A joke in the industry is that you can (and I have actually seen people do it) weld directly off of one. They simply do not work. A friend of mine hired a contractor to remodel their kitchen and install an under counter electric range in addition to the other one they had. The contractor Did not have room in the panel so he double tapped 2 single pole 20a breakers...... One of the 20's fed recepts that were commonly used to vacuum the house ( about 14 amps for a good vacuum and The range pulled 40 amps with both elements on ) They used it that way for years and when they did they always smelled a foul odor. Come to find out the odor was the oil in the Bakelite recepts and romex in the walls cooking off. Poor install into a poor system almost burned down the entire house.....
Disclaimer again. The content above is not cited and is given with the express use that the reader takes the information and use it at their own risk. no guarantee expressed or implied. The above was written to give an insight to how electricity works not the exact science of it
ETA: Here are some cool youtube videos
http://www.youtube.com/watch?v=uMV1jmDn3o4
http://www.youtube.com/watch?v=MkVMCAPnKGY
