Different 220volt plugs

[Phill Tibbetts]

Why are some 200 volt single phase plugs 3 prong and some 4 prong? What happens if you use 3 prong in a 4 prong receptacle. Just wondering as my welder has a 3 prong plug and my generator has 4 prong. Tesla uses a 4 prong plug when you use their adapter for home charging. I also know that 220 v only needs 2 wires and no ground to work. I'm sure there is a reason for this but curious.

 

[m16ty]

4 prong 220v is for appliances that require a neutral, usually because the appliance also has 120v loads. I have no idea why the Tesla uses a neutral, but that’s what the 4th prong is for.

Yes, you can use a 3 prong plug into a 4 prong socket, as long as they will plug together.

 

[a49deere]

Why are some 200 volt single phase plugs 3 prong and some 4 prong? What happens if you use 3 prong in a 4 prong receptacle. Just wondering as my welder has a 3 prong plug and my generator has 4 prong. Tesla uses a 4 prong plug when you use their adapter for home charging. I also know that 220 v only needs 2 wires and no ground to work. I'm sure there is a reason for this but curious.

Why are some 200 volt single phase plugs 3 prong and some 4 prong? What happens if you use 3 prong in a 4 prong receptacle. Just wondering as my welder has a 3 prong plug and my generator has 4 prong. Tesla uses a 4 prong plug when you use their adapter for home charging. I also know that 220 v only needs 2 wires and no ground to work. I'm sure there is a reason for this but curious.

3 won't fit in a 4 prong. 3 prong is two phases and ground, 4 prong is two phases, neutral and ground. welder is straight 220/240 with a ground, your generator when using the 4-prong outlet provides not only 220, but two separate 120 circuits plus ground, such as when using for your home backup power.

 

[Tony in SD]

The new code for stoves and dryers requires a 4 Prong plug. 1) an earth ground, 2) neutral, 3) L1 & 4) L2 (hot legs).
RVs use a NEMA 14-50P which has an earth ground, neutral, and two 50 amp 125 vac to neutral circuits. One circuit L1 to neutral and the other L2 to neutral. It is very rare for an RV to have any 240 vac appliances but they are feed with a 240 plug.

 

[a49deere]

The new code for stoves and dryers requires a 4 Prong plug. 1) an earth ground, 2) neutral, 3) L1 & 4) L2 (hot legs).
RVs use a NEMA 14-50P which has an earth ground, neutral, and two 50 amp 125 vac to neutral circuits. One circuit L1 to neutral and the other L2 to neutral. It is very rare for an RV to have any 240 vac appliances but they are feed with a 240 plug.

they are fed with a 240-volt cord/plug because the RV loads can be split between the two phases balancing the load more evenly on your generator.

 

[Phill Tibbetts]

All very interesting, thanks to everyone. I remember years ago an electrician told me to make sure I used a 4 prong plug when I hooked up my backup generator so it would balance the load from the house.

 

[MarkB_MI]

All very interesting, thanks to everyone. I remember years ago an electrician told me to make sure I used a 4 prong plug when I hooked up my backup generator so it would balance the load from the house.

Well, yes! It would be very bad to omit the neutral connection when connecting a generator to your home, since it could result in your 120 volt appliances getting anything between zero and 240 volts.

Note that you don't necessarily need a GROUND connection between your home and your generator, but you definitely need a NEUTRAL connection. John T might weigh in on this as he has some pretty strong opinions about floating versus grounded generators.

 

[a49deere]

Well, yes! It would be very bad to omit the neutral connection when connecting a generator to your home, since it could result in your 120 volt appliances getting anything between zero and 240 volts.

Note that you don't necessarily need a GROUND connection between your home and your generator, but you definitely need a NEUTRAL connection. John T might weigh in on this as he has some pretty strong opinions about floating versus grounded generators.

A lot of the newer generators have a bonded neutral, they also have a GFCI protected 220volt outlet. This is fine if using the generator for task that don't involve a home bonded service. More than likely when these types of generators are used for home back up, the bond between ground and neutral will need to be removed at generator head so as to not to trip GFCI. This is when you need /should drive a ground rod and ground generator with ground lug normally supplied on generator.

 

[miangus]

I would avoid driving a separate ground rod for a generator. It really does not provide protection for users; bonding is what provides protection against electrification. If the generator has a bonded neutral and the generator frame becomes energized, it should trip the breaker. If the generator has been unbonded and the frame becomes energized the ground rod will also be energized creating a step potential. The breaker will not trip.

 

[drsportster]

A supply house will have a chart on the counter If you don't use the chart you risk getting the wrong ones.

 

[chvet73]

A supply house will have a chart on the counter If you don't use the chart you risk getting the wrong ones.

https://cdn.shopify.com/s/files/1/0853/8964/files/NEMA_plug_chart_some_rotated_480x480.jpg?v=1605127706

Just to add further confusion check the many varieties of 220 plugs that are out there.

 

[a49deere]

I would avoid driving a separate ground rod for a generator. It really does not provide protection for users; bonding is what provides protection against electrification. If the generator has a bonded neutral and the generator frame becomes energized, it should trip the breaker. If the generator has been unbonded and the frame becomes energized the ground rod will also be energized creating a step potential. The breaker will not trip.

good luck getting a generator with a GFCI protected 220-volt outlet to hold on a home service that has a bonded neutral and ground! You do know that when unbounding a generator and using the correct 4 conductor cable the frame of the generator is grounded through the service in the home! The one time that you would not want to unbond the generator was if you have a transfer switch that breaks the neutral as well as the phase conductors!

 

[Ray,IN]

Why are some 200 volt single phase plugs 3 prong and some 4 prong? What happens if you use 3 prong in a 4 prong receptacle. Just wondering as my welder has a 3 prong plug and my generator has 4 prong. Tesla uses a 4 prong plug when you use their adapter for home charging. I also know that 220 v only needs 2 wires and no ground to work. I'm sure there is a reason for this but curious.

Although this website is for RV's, it explains your questions in detail. https://www.myrv.us/electric/

 

[MarkB_MI]

Although this website is for RV's, it explains your questions in detail. https://www.myrv.us/electric/

Only 50 amp RV service is 240 volts. 30 amp RV service is 120 volts. So a 30 amp RV plug is not the same thing as a three-prong 240V 30 amp dryer plug.

 

[Ray,IN]

Only 50 amp RV service is 240 volts. 30 amp RV service is 120 volts. So a 30 amp RV plug is not the same thing as a three-prong 240V 30 amp dryer plug.

Right, and the plug prongs are different! Many professional electricians have made that mistake when wiring in an RV receptacle at a house. The old horror stories are found on any RVing discussion forum website.

 

[Tony in SD]

Right, and the plug prongs are different! Many professional electricians have made that mistake when wiring in an RV receptacle at a house. The old horror stories are found on any RVing discussion forum website.

The 30 amp RV plug is easy to wire wrong. I've seen electricians wire it wrong. That is why I always carry my Fluke meter and check the voltage before i plug in my RV

 

[John T]

Why are some 200 volt single phase plugs 3 prong and some 4 prong?

Good question Phil, here's the reason plus other FYI:

A typical 240 Volt 3 Prong receptacle is for 240 ONLY (IE NO 120) tools, like say a motor or welder etc., and has 240 L1 to L2 plus a safety Equipment Grounding Conductor EGC. NOTE this EGC is not necessarily the same as what some might call an "earth ground" but that's a whole other thread.

A typical 4 prong 240 Volt Receptacle has 2 Hots L1 and L2 (240 L1 to L2), a Neutral Conductor (120 L1 or L2 to Neutral), plus an EGC.

Some old appliances that only used a 3 prong receptacle but had both 240 and 120 loads, used the EGC as a Neutral which is long now forbidden.

Modern appliances that have BOTH 120 (such as clocks or electronics or 120 receptacles) and 240 (such as heating elements) internal loads therefore use a 4 prong receptacle such that the 120 volt loads have a Neutral current return versus returning it via the EGC

Many portable gensets supply 120 volts as well as 240 volts and are configured similar to how households are having BOTH 240 Line to Line as well as two legs of 120 L1 or L2 to Neutral. They may have a 4 prong receptacle (similar to the above) plus maybe a standard 120 Volt 15/20 Amp Receptacle, maybe a 30 amp 120 volt 3 prong RV TT 30R receptacle.

Many smaller portable gensets come from the factory with a Floating Neutral, others a Bonded Neutral. There are reasons when and why a Floating Neutral should be used versus a Bonded Neutral, but that's beyond your question. Basically its if or how a genset is connected to your home that determines if the Genset has a Floating versus a Bonded Neutral. Just another FYI there are times when a Grounding Electrode (such as a rod driven into earth) is required when using a portable genset and others its NOT required, another thread but a brief example a single RV powered by a genset does NOT require connection to a Grounding Electrode. A basic FYI rule is that there shall be ONLY ONE Neutral Ground Bond.

John T Retired n rusty power engineer but believe this to be accurate yet NO warranty, consult the NEC.

 

[John T]

I would avoid driving a separate ground rod for a generator.

GENERALY SPEAKING ONLY there are times when connection to a Grounding Electrode (such as but not limited to a rod driven into earth) is required for portable gensets and others when its not (but its more complicated than only one sentence) thats my current understanding of the NEC but no warranty consult it NOT me lol see my post above

PS its my recollection that per OSHA for construction site gensets you are RIGHT they may use a Bonded Neutral BUT DONT WANT connection to a rod driven into earth !!!!!!!!!!! Old memory noooooooooo warranty grrrrrrrrrrrrrrr

Nice sparky chatting with you Im trying to stay out of the weeds on this to avoid confusion to non electricians but such happens lol

John T