50 Amp to Welder outlet

[fez111]

I'm going to muddy up the water a bit here. I have never personally seen this, but I wasn't necessarily looking for it either. I've heard this for the last couple of years, that there are RV parks (newer ones being built) that are now using 208 3phase Wye from the transformers that provide power to the pedestals at their campgrounds. Has anyone here....who actually knows what I'm talking about, seen that scenario? On that power pedestal, you would read the following voltages. L1 to neutral 120VAC, L2 to neutral 120VAC and then from L1 to L2 the reading would be 208. Anyone seen it out there. Most folks wouldn't ever notice it unless they use a meter and test voltage before they plug into the pedestal power, and got 208 instead of the more normal voltages seen with a Split phase system of 230-240V

I'm going to muddy it up even more... I cannot confirm nor deny what you are saying about some RV parks, but I do know the following...

The main difference for using 208 volts instead of 220-240 is that in the U.S. our standard 'lower' distributed voltage is 460-480 volts three-phase. That gets stepped down to 220-240 three-phase for residential and smaller industrial distribution. Although there are some areas of the U.S that do distribute 208 volt three-phase power, that is seldom used to derive 110 volt residential voltage. I believe that, but I may be mistaken, 208 volts is derived through delta transformers, not wye, for the purpose of better balancing of the phase voltages.

Also, doing the math, in the U.S. we use 60 cycles per second. In much of Europe they use 50 cycles per second. Using a lower frequency at 220-240 with inductive loads (i.e. motors and transformers) causes the current to be higher and cause more heat. To remedy this problem they use 208 volts predominately with 50 cycles. Doing even more math, many motors sold for use around the world have both 50 and 60 Hertz frequencies listed on their data plates. At 50 Hertz the motors are rated 208 volts and at 60 Hertz are rated 220-240 volts. With both of these ratings the rated horsepower is the same. They have to reduce the voltage for 50 Hertz because less frequency means less electromotive resistance and more current and heat.

One more thing about 208 volts. In the industrial robot world, robot motors are operated by taking direct current voltage (think batteries) and using frequency inverters (servo amps) to create/generate the proper operating frequencies needed for the speeds required. Using a formula from the National Electrical Code that involves the square root of 3 to calculate, 208 volt three-phase voltage converts perfectly into a 300 volt DC voltage supply (think battery again). I have worked in many Japanese auto plants where their entire operations are powered with 208 volts three phase for that exact purpose. Just my 52 cents worth.

I apologize for the litany above. Its what I do. School is out. You all got A's.

[fez111]

This is correct, and even the neutral could be overloaded. With predominantly 240V or balanced loads, the neutral can be smaller than the hot wires. Strange as it sounds, with perfectly balanced 120V loads the average neutral current is 0. When you start pulling near rated capacity from only one hot, the neutral can be overloaded and it isn’t protected by a breaker or fuse.

Everything you said is completely true. However, the National Electrical Code states that the neutral wire cannot be a smaller than the line wires... And the reason the neutral wire current can conceivably be zero is because the two phases are 120 degrees out of phase.

[xrated]

Everything you said is completely true. However, the National Electrical Code states that the neutral wire cannot be a smaller than the line wires... And the reason the neutral wire current can conceivably be zero is because the two phases are 120 degrees out of phase.

The TWO phases are NOT 120 degrees out of phase with each other....they are 180 degrees out of phase. Maybe you are thinking three phase power.....in that, the three phases are 120 degrees out of phase....A to B....B to C....and A to C.

[xrated]

I'm going to muddy it up even more... I cannot confirm nor deny what you are saying about some RV parks, but I do know the following...

The main difference for using 208 volts instead of 220-240 is that in the U.S. our standard 'lower' distributed voltage is 460-480 volts three-phase. That gets stepped down to 220-240 three-phase for residential and smaller industrial distribution. Although there are some areas of the U.S that do distribute 208 volt three-phase power, that is seldom used to derive 110 volt residential voltage. I believe that, but I may be mistaken, 208 volts is derived through delta transformers, not wye, for the purpose of better balancing of the phase voltages.

Also, doing the math, in the U.S. we use 60 cycles per second. In much of Europe they use 50 cycles per second. Using a lower frequency at 220-240 with inductive loads (i.e. motors and transformers) causes the current to be higher and cause more heat. To remedy this problem they use 208 volts predominately with 50 cycles. Doing even more math, many motors sold for use around the world have both 50 and 60 Hertz frequencies listed on their data plates. At 50 Hertz the motors are rated 208 volts and at 60 Hertz are rated 220-240 volts. With both of these ratings the rated horsepower is the same. They have to reduce the voltage for 50 Hertz because less frequency means less electromotive resistance and more current and heat.

One more thing about 208 volts. In the industrial robot world, robot motors are operated by taking direct current voltage (think batteries) and using frequency inverters (servo amps) to create/generate the proper operating frequencies needed for the speeds required. Using a formula from the National Electrical Code that involves the square root of 3 to calculate, 208 volt three-phase voltage converts perfectly into a 300 volt DC voltage supply (think battery again). I have worked in many Japanese auto plants where their entire operations are powered with 208 volts three phase for that exact purpose. Just my 52 cents worth.

I apologize for the litany above. Its what I do. School is out. You all got A's.

The "normal" 208V 3phase power comes from a Wye wound transformer and is quite common in commercial/offices and is used largely in those instances for Lighting panels and for 120V receptacles. It can also be used for "low voltage" three phase motors.....as in dual voltage motors that can be 480V or 208V.....both of them being three phase. The only 208V 3 phase Delta that I know is is when you have a "wild leg" configuration.

[jkwilson]

Everything you said is completely true. However, the National Electrical Code states that the neutral wire cannot be a smaller than the line wires... And the reason the neutral wire current can conceivably be zero is because the two phases are 120 degrees out of phase.

The NEC only prohibits downsizing the neutral in a 120/208 3-wire circuits or when powering significantly non-linear loads. Otherwise, the neutral can be sized to carry only the unbalanced load on the circuit which can be very small. Most household power is derived from the sides of a single transformer which makes the lines 180 degrees out of phase rather than the 120 you’d see with three phase.