4 Prong Electrical Plug

[Glenn F.]

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

Thank you,
Glenn F.

 

[wp6529]

Looks like a regular 50A 125/250V receptacle, used for RVs, welders, some larger electric stoves, etc.

 

[Loosehandle]

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

Thank you,
Glenn F.

My welders all have 3 prongs, but are older. I believe this 4 prong gives you neutral and ground.

 

[DoubleO7]

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

Thank you,
Glenn F.

14-50P for 125/250V
Current code for most anything new.

 

[stevieb49829]

My welders all have 3 prongs, but are older. I believe this 4 prong gives you neutral and ground.

What I heard was that for modern day 220 appliances, which have electronic controls, they had to be able to split off 110 volts to run the electronics, which didn't work when only a ground was used as the 3rd leg. Or was it the neutral as the 3rd leg? I obviously don't know what I'm talking about! steve

 

[MarkB_MI]

Most common use would be for 50 amp RV service or an electric range. Current code sez dryers and ranges need four-wire service; that's been code for mobile home appliances for a long time.

 

[Tony in SD]

50 amp RV / some welders / kitchen range. Maybe other uses as well. Line 1, line 2, neutral, ground.

 

[Janicholson]

What I heard was that for modern day 220 appliances, which have electronic controls, they had to be able to split off 110 volts to run the electronics, which didn't work when only a ground was used as the 3rd leg. Or was it the neutral as the 3rd leg? I obviously don't know what I'm talking about! steve

Almost. There was no true equipment ground (unless run to a pipe or separate rod. The neutral was used as the 120v leg. The 240 was across L1 to L2 with the Neutral not used for the higher voltage. Jim

 

[stevieb49829]

Almost. There was no true equipment ground (unless run to a pipe or separate rod. The neutral was used as the 120v leg. The 240 was across L1 to L2 with the Neutral not used for the higher voltage. Jim

Thanks, Jim. So to continue this, is the 4th contact on the modern plugs for ground? And why then does the 3 wire plug on my welder have two hots and no neutral? Because to get the 240 for the welder, you only need the two hots, and the third leg is equipment ground? steve

 

[wp6529]

Modern appliances are more likely to be true 240V only due to wide input range switch-mode power supplies being extremely common. In the old days electric clothes dryers would have 240V heating coils and sometimes motors but the timer controls had 120V motors and used the neutral as the return to get the 120V they needed. Everything today is electronic controls, inverter drives to motors, etc. and most likely just using 240V only.

Welders have pretty much always been 240V only with no need for a neutral, just the two hots of the 240V and a ground. My Syncrowave 250 even has a 120V receptacle on it to power the water cooler for the TIG torch and it is still 240V or 480V only input. The 120V for the receptacle is derived in the main transformer of the welder so still no neutral required on the supply side. Also nice since it is still correct 120V when the welder is being powered from 480V.

At any rate, beyond code, if installing a new receptacle it makes sense to run the extra conductor so you have the flexibility of having 120/240V available.

 

[NoDakInMN]

Thanks, Jim. So to continue this, is the 4th contact on the modern plugs for ground? And why then does the 3 wire plug on my welder have two hots and no neutral? Because to get the 240 for the welder, you only need the two hots, and the third leg is equipment ground? steve

Even though grounds and neutrals land on the same terminals in the breaker box, a neutral has to be an identified conductor (like the white wire on a 120 V circuit) to differentiate it as a current carrying conductor as opposed the ground.

 

[John T]

Mornin Glenn, good question so for you and other non sparkles here’s the deal

The receptacle shown is identified as a 3 Pole 4 Wire NEMA 14-50R Grounding Outlet. It has the two Hot UnGrounded L1 & L2 conductors slots side by side,,the center slot is the Grounded Conductor aka Neutral and the rounded slit is for the Equipment Grounding Conductor. It’s 240 line to line but 120 from either line to Neutral. It can supply a 50 amp rv with two legs of 120 and other tools or appliances that require both 120 and 240 which is why the neutral and ground are both available

If a 240 volt only welder is used a 3 prong plug and receptacle can suffice as it has 240 line to line and the third wire safety ground.

While 50 amp rv is a common use a range or maybe a welder that needs 120 and 240 could use such a receptacle. The grounded conductor neutral is for normal return current while then EGC is ONLY for fault current.
Hope this answers your question
Post back any other questions.

Best wishes

John T

 

[Mike(NEOhio)]

The four wire separates neutral and ground. A three wire uses the neutral as ground and the equipment has some type of bond from the frame to neutral. I converted our electric dryer from three to four because the duct started to arc to a nearby water pipe. Never happened in 40 plus years but it did it after a new dryer was installed.

 

[Janicholson]

Thanks, Jim. So to continue this, is the 4th contact on the modern plugs for ground? And why then does the 3 wire plug on my welder have two hots and no neutral? Because to get the 240 for the welder, you only need the two hots, and the third leg is equipment ground? steve

The neutral to the 3 wire device is from old code era that allowed it to carry that responsibility even if there was no actual load flowing in it. It also provided a path for induced voltage from the secondary windings and arc EMF. Jim

 

[wp6529]

The neutral to the 3 wire device is from old code era that allowed it to carry that responsibility even if there was no actual load flowing in it. It also provided a path for induced voltage from the secondary windings and arc EMF. Jim

To be clear, three prong, three wire receptacles do not have a neutral connection. 250V 3 wire, just two hots and ground. This is not something old or obsolete. The old and obsolete was three wire 250V with ground being allowed to place small 120V loads across one hot and the ground, thereby causing current flow in the grounding conductor and raising it above ground potential. The grounding conductor is only allowed to carry fault current now.

The neutral is the grounded conductor, is not connected to the metal chassis of most devices and is insulated all the way back to the service panel where the bond to ground is. The neutral is expected to be carrying current and not at ground potential which is why it is insulated. The grounding conductor is commonly uninsulated and is typically connected to metal equipment chassis.

 

[stevieb49829]

To be clear, three prong, three wire receptacles do not have a neutral connection. 250V 3 wire, just two hots and ground. This is not something old or obsolete. The old and obsolete was three wire 250V with ground being allowed to place small 120V loads across one hot and the ground, thereby causing current flow in the grounding conductor and raising it above ground potential. The grounding conductor is only allowed to carry fault current now.

The neutral is the grounded conductor, is not connected to the metal chassis of most devices and is insulated all the way back to the service panel where the bond to ground is. The neutral is expected to be carrying current and not at ground potential which is why it is insulated. The grounding conductor is commonly uninsulated and is typically connected to metal equipment chassis.

Those three replies just explained it the way I thought it worked, but wasn't sure. Thanks, Jim, WP, and NoDak.

 

[John T]

Thanks, Jim. So to continue this, is the 4th contact on the modern plugs for ground? And why then does the 3 wire plug on my welder have two hots and no neutral? Because to get the 240 for the welder, you only need the two hots, and the third leg is equipment ground? steve

Stevie, yes the 4th contact is the Equipment Grounding Conductor. However if a welder requires straight 240 volt only a 3 pin plug suffices for the two hot 240 volts while the third is the safety ground.

Remember The grounded conductor aka neutral is for normal return current while the EGC is ONLY for fault current.
Got it ?? If not post back

John T

 

[John T]

What I heard was that for modern day 220 appliances, which have electronic controls, they had to be able to split off 110 volts to run the electronics, which didn't work when only a ground was used as the 3rd leg. Or was it the neutral as the 3rd leg? I obviously don't know what I'm talking about! steve

Stevie you’re asking good questions and that’s the best way to learn. In the old days with only two hot legs and a ground there would be 120 from either hot to ground so they were using the ground as a live current carrying conductor and the ground could be bonded to outer metallic case frames of appliances whic you touch and that could be a hazard. So modern wiring used the insulated neutral to carry return current not the bare geeen ground wire which may be connected to the tools case. Ground for fault current only neutral for live normal return curent it’s insulated so you don’t touch it John T

 

[Janicholson]

Stevie you’re asking good questions and that’s the best way to learn. In the old days with only two hot legs and a ground there would be 120 from either hot to ground so they were using the ground as a live current carrying conductor and the ground could be bonded to outer metallic case frames of appliances whic you touch and that could be a hazard. So modern wiring used the insulated neutral to carry return current not the bare geeen ground wire which may be connected to the tools case. Ground for fault current only neutral for live normal return curent it’s insulated so you don’t touch it John T

Reality was a hazard! and other than that could still be! Jim

 

[stevieb49829]

Stevie, yes the 4th contact is the Equipment Grounding Conductor. However if a welder requires straight 240 volt only a 3 pin plug suffices for the two hot 240 volts while the third is the safety ground.

Remember The grounded conductor aka neutral is for normal return current while the EGC is ONLY for fault current.
Got it ?? If not post back

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