4 Prong Electrical Plug

[Janicholson]

John, So, if I want to use 110v (one hot leg), my neutral will be running current, but if I want only the 220/240, (both hot legs) the neutral won't have any current in it? I'm ignoring the ground circuit in this. steve

Assuming a pure 240 volt appliance (resistive or magnetic) the "grounded at the entrance panel" neutral will not have current. The 240 single phase Scope trace passes, at zero volts, exactly through the point that 120v would be at zero volts. So only using 120 would push current through the neutral. Jim

 

[wp6529]

John, So, if I want to use 110v (one hot leg), my neutral will be running current, but if I want only the 220/240, (both hot legs) the neutral won't have any current in it? I'm ignoring the ground circuit in this. steve

If you only need 240V the neutral is not connected at all. The ground usually will be connected though it might not if the device is "double insulated".

 

[John T]

John, So, if I want to use 110v (one hot leg), my neutral will be running current, but if I want only the 220/240, (both hot legs) the neutral won't have any current in it? I'm ignoring the ground circuit in this. steve

Hi Stevie another good question. Yes it’s 120 across one hot and neutral and the neutral carries the current returned from the load. If you place a 240 volt load across the two hots they carry the current and none in the neutral it’s not in that pure 240 volt circuit it’s not connected to anything just sitting there no current flows in it You got it my friend. !!!

John T

 

[stevieb49829]

Assuming a pure 240 volt appliance (resistive or magnetic) the "grounded at the entrance panel" neutral will not have current. The 240 single phase Scope trace passes, at zero volts, exactly through the point that 120v would be at zero volts. So only using 120 would push current through the neutral. Jim

Jim, I didn't understand much of that reply, but I am curious about why there is no "return path" when using both legs of the 220. I think it has something to do about the phases in each leg, but I don't understand that at all. Obviously, I'm not a Sparky kind of guy steve

 

[Janicholson]

Jim, I didn't understand much of that reply, but I am curious about why there is no "return path" when using both legs of the 220. I think it has something to do about the phases in each leg, but I don't understand that at all. Obviously, I'm not a Sparky kind of guy steve

The neutral is not attached to the component Resistor or magnetic load at all. An because of this the device "sees" a complete 60cycle 240 volts and uses the one leg to deliver the rising sine wave voltage and the other to act as a neutral. then the wave form goes back to Zero volts (one half way through the cycle) then the other hot leg becomes the supply and the first duplicates a neutral.
If 120 is desired, the neutral is used and the voltage to that does the same thing over the same amount of time but the supplied voltage is only one half as big. AC voltage is measured in our power grids by RMS value. This would be the same as equivalent power of DC voltage. is ,707 of the actual peak to peak voltage. Peak to Peak voltage on 120 AC is 169.7 volts. Jim

 

[MarkB_MI]

Jim, I didn't understand much of that reply, but I am curious about why there is no "return path" when using both legs of the 220. I think it has something to do about the phases in each leg, but I don't understand that at all. Obviously, I'm not a Sparky kind of guy steve

Jim, I didn't understand much of that reply, but I am curious about why there is no "return path" when using both legs of the 220. I think it has something to do about the phases in each leg, but I don't understand that at all.

Kirchoff's Current Law says the sum of the current into a node must equal the sum of the current out of the node. If you consider your dryer, for example, to be a 'node', it has three conductors attached to it: Two hots and a neutral. Now if you have only 240 volt loads in the dryer, then the current going into one hot is equal to the current going out the other hot, so there's no current flowing in the neutral conductor. However, there are in fact small 120 volt loads in the dryer; the timer and various control devices are 120 volt, maybe the motor as well. Additional current must flow through one of the hot legs to power the 120 volt devices. That current has to go out somewhere, and that somewhere is the neutral conductor.

 

[miangus]

The neutral is not attached to the component Resistor or magnetic load at all. An because of this the device "sees" a complete 60cycle 240 volts and uses the one leg to deliver the rising sine wave voltage and the other to act as a neutral. then the wave form goes back to Zero volts (one half way through the cycle) then the other hot leg becomes the supply and the first duplicates a neutral.
If 120 is desired, the neutral is used and the voltage to that does the same thing over the same amount of time but the supplied voltage is only one half as big. AC voltage is measured in our power grids by RMS value. This would be the same as equivalent power of DC voltage. is ,707 of the actual peak to peak voltage. Peak to Peak voltage on 120 AC is 169.7 volts. Jim

Excellent explanation. It all starts at the residential service transformer, where one could argue that the US has a 240-volt system. However, to provide the flexibility and safety of a lower voltage the transformer is center tapped which creates a neutral source that provides 120 volts with reference to each of the legs. This discussion explains why there are three common 240-volt 50-amp plugs. The old three prong with two hot wires and a neutral usually called a range plug, the four prong plug usually referred to as a dryer plug, which has two hot wires, a neutral and a ground and the three prong plug which has no neutral and only serves 240 Volt loads commonly called a welder plug.

 

[RedMF40]

What is this plag used for? I don’t think I’ve seen a four prong plug before.

Thank you,
Glenn F.

My electric dryer has that kind of plug. I had to change it when I bought a new dryer and seem to recall it had 2 hots, a neutral and a ground. Can't say for sure. Friend who's a master electrician checked my work to make sure it was correct.

 

[Watthour]

The assumption of balanced loading relies upon the further assumption that the load does not have leakage. When a load is inductive, such as a transformer, squirrel cage motor, or the front end of a drive with chokes, eddy currents induced into the core laminations of that transformer/choke or even the shaft of that motor can leak to ground. This is frequently exposed in motors by the bearings being etched prematurely, or in drives, the control electronics sensing ground leakage. With the proliferation of higher-end electronics being introduced into everything from welders to washing machines, the presence of more brushless/servomotors, and frequency control, this will become an increasing phenomenon. That grounded conductor will be put to greater use and the grounding conductor must be separated to maintain safety.

 

[Janicholson]

The assumption of balanced loading relies upon the further assumption that the load does not have leakage. When a load is inductive, such as a transformer, squirrel cage motor, or the front end of a drive with chokes, eddy currents induced into the core laminations of that transformer/choke or even the shaft of that motor can leak to ground. This is frequently exposed in motors by the bearings being etched prematurely, or in drives, the control electronics sensing ground leakage. With the proliferation of higher-end electronics being introduced into everything from welders to washing machines, the presence of more brushless/servomotors, and frequency control, this will become an increasing phenomenon. That grounded conductor will be put to greater use and the grounding conductor must be separated to maintain safety.

Yes. (I think I indicated that in my post above) the control of "leakage" is GFIC and spark detection circuitry. Both are getting quite a bit of active duty, and attention. Properly used, those devices will keep electrons in motion out of that equipment ground path. Jim

 

[JMOR]

The neutral is not attached to the component Resistor or magnetic load at all. An because of this the device "sees" a complete 60cycle 240 volts and uses the one leg to deliver the rising sine wave voltage and the other to act as a neutral. then the wave form goes back to Zero volts (one half way through the cycle) then the other hot leg becomes the supply and the first duplicates a neutral.
If 120 is desired, the neutral is used and the voltage to that does the same thing over the same amount of time but the supplied voltage is only one half as big. AC voltage is measured in our power grids by RMS value. This would be the same as equivalent power of DC voltage. is ,707 of the actual peak to peak voltage. Peak to Peak voltage on 120 AC is 169.7 volts. Jim

Not peak-to-peak, 169 is simply peak. Double that for peak-to-peak (339.4).

 

[MarkB_MI]

The assumption of balanced loading relies upon the further assumption that the load does not have leakage. When a load is inductive, such as a transformer, squirrel cage motor, or the front end of a drive with chokes, eddy currents induced into the core laminations of that transformer/choke or even the shaft of that motor can leak to ground. This is frequently exposed in motors by the bearings being etched prematurely, or in drives, the control electronics sensing ground leakage. With the proliferation of higher-end electronics being introduced into everything from welders to washing machines, the presence of more brushless/servomotors, and frequency control, this will become an increasing phenomenon. That grounded conductor will be put to greater use and the grounding conductor must be separated to maintain safety.

When a load is inductive, such as a transformer, squirrel cage motor, or the front end of a drive with chokes, eddy currents induced into the core laminations of that transformer/choke or even the shaft of that motor can leak to ground.

Hmm. So you're saying current induced by an AC circuit can somehow drain current from that circuit? That does not happen, assuming the circuit is properly insulated. Kirchoff's Current Law applies always.

Eddy currents in a motor or transformer do not exit the device. That would be a violation of Kirchoff's Current Law. It is, however, possible to have a ground loop, where induced currents travel through multiple ground connections. But those currents do not affect the net balance of current in the circuit that induced them. If there is an imbalance in the current entering and leaving a device, there is a short circuit somewhere in the device.

 

[stevieb49829]

I'm outa here. I got my answer, to the best of my understanding. steve

 

[John T]

I'm outa here. I got my answer, to the best of my understanding. steve

Glad you got the help you need Don’t feel bad if the chat got so deep in the weeds you felt lost, that can easily happen anytime sn electrical question is posted here and there are a ton of answers both by lay persons as well as a few engineers and professional electricians who help out here, all a bunch of good gents trying their best to help. Often someone posts an answer but it’s just NOT to the question asked lol and things go off on a tangent that may last for days until the poor old horse is beat to death. I’m guilty as anyone and enjoy helping anytime and it’s fun reading the comments.

Best wishes to all here and for all the help people provide

John T. Stephen Foster State Park old tractor show White Springs Florida

 

[JMOR]

I'm outa here. I got my answer, to the best of my understanding. steve

Especially for stevieb: the transformer is on elect co pole

https://imgur.com/bt1WJkX

 

[stevieb49829]

Especially for stevieb: the transformer is on elect co pole

https://imgur.com/bt1WJkX

Yup, when folks with a lot more knowledge in electicity start talking about wave forms and scopes, I just stick my fingers in my ears and hum a tune. I understand what they are talking about, I just don't have the need to understand it that deeply. Knowing that L1 and L2 cancel themselves (because of their wave patterns), so there is no need for neutral was all I needed to confirm why my welder was only using a ground, and not a neutral. steve

 

[JMOR]

Yup, when folks with a lot more knowledge in electicity start talking about wave forms and scopes, I just stick my fingers in my ears and hum a tune. I understand what they are talking about, I just don't have the need to understand it that deeply. Knowing that L1 and L2 cancel themselves (because of their wave patterns), so there is no need for neutral was all I needed to confirm why my welder was only using a ground, and not a neutral. steve

Gotcha! added more for others

https://imgur.com/E7vb1DJ

 

[JMOR]

Gotcha! added more for others

https://imgur.com/o1AJstz

 

[buickanddeere]

Back in the bad old days they tried to make do with a three prong . Sharing the neutral and ground on one prong for electric clothes dryers and electric cook stoves .
Was not uncommon for People using them to receive shocks .

 

[buickanddeere]

Surprising how many people have never seen a proper 120/240 four prong plug and receptacle . In order to separate the ground and the neutral .
I do realize that there are some people that no matter how many times they are told and what proof is provided . They perceive no need for a four prong plug receptacle .