3 prong 50 amp plug to 4 prong 50 amp ????

Dutch_12078 wrote:

Groover wrote:
As others have observed there are only three wires coming into the house and both ground and nuetral go to the same bus in the breaker box. The reason for two wires going to the same place is redundancy to reduce the risk of a wiring failure preventing a proper ground and possibly leading to someone getting hurt. As a society we got by without it for many years but decided about 15 years ago to improve safety by doubling up.

If you look closely at the panel photo above, there are actually 4 wires coming in to the box. The two hots and neutral come in through the center conduit, and the safety ground from the outside ground post comes in at the upper left.

I meant from the utility company and am just suggesting that the same setup with a new ground would work on the outlet. If they need to be tied together as they are in the breaker box to be more effective that could be done in the outlet box as well. It might be a lot easier than pulling a new wire all the way back to the breaker box. Personally, I pulled 4 wires to my RV and still added a new ground rod. By the way, the purpose built RV power box I bought (just like the ones in campgrounds) have the ground and nuetral joined together in the box.

Groover wrote:
As others have observed there are only three wires coming into the house and both ground and nuetral go to the same bus in the breaker box. The reason for two wires going to the same place is redundancy to reduce the risk of a wiring failure preventing a proper ground and possibly leading to someone getting hurt. As a society we got by without it for many years but decided about 15 years ago to improve safety by doubling up.

If you look closely at the panel photo above, there are actually 4 wires coming in to the box. The two hots and neutral come in through the center conduit, and the safety ground from the outside ground post comes in at the upper left.

Groover wrote:
As others have observed there are only three wires coming into the house and both ground and nuetral go to the same bus in the breaker box. The reason for two wires going to the same place is redundancy to reduce the risk of a wiring failure preventing a proper ground and possibly leading to someone getting hurt. As a society we got by without it for many years but decided about 15 years ago to improve safety by doubling up.

So, if I were in this situation, I would first check to be sure that the 3-prong plug has the same size ground wire as hot wire. It most likely does. I would take out the 3 prong plug and replace it with a 4 prong plug then run at least a 10 guage wire from the neutral terminal to either the electrical panel or a ground rod. The addition of the ground rod is what lets the utility company get away with only one neutral wire going to the house. A new ground rod at the plug provides the same security that the rest of the house has. This wire does not have to be insulated any more than the one from the panel to the existing ground rod. A ground rod can be added near the outlet by drilling a hole in the floor and driving the rod in. Follow the wiring instructions from GlenLever and you will be good.

A separate ground wire back to the panel is acceptable and IIRC approved by code for updating older non-grounded circuits. For the relatively older three-wire dryer and range circuits, there is a neutral but no separate safety ground, and this neutral should be sized the same as the two hots. (It is also possible to have 220V circuits and receptacles that have a ground but no neutral for devices that only use 220V power, such as welders or other larger power tools, and for these the ground conductor is not a current carrying conductor and may sometimes be undersized relative to the others. Most of the common 220V only devices in residential use—water heaters, well pumps, central air conditioners—are hardwired, so this isn't especially common in homes.)

A separate ground wire running to a separate ground rod does not provide the same sort of protection because the impedance between the new ground rod and the neutral/ground bus in the panel is not insignificant. A ground fault in the motorhome (a hard short from hot to ground) may not cause the breaker to trip because the current flow through the ground is limited by this impedance.

The purpose of the ground rod or equivalent is to make sure the overall potential of the electrical system, and the neutral bus in particular, doesn't float too far from the potential of the general environment. The purpose of the ground wire going back to the breaker box is to provide protection against a fault in the wiring or in the chassis of a device that is connected. They're somewhat related purposes, but not identical.

As others have observed there are only three wires coming into the house and both ground and nuetral go to the same bus in the breaker box. The reason for two wires going to the same place is redundancy to reduce the risk of a wiring failure preventing a proper ground and possibly leading to someone getting hurt. As a society we got by without it for many years but decided about 15 years ago to improve safety by doubling up.

So, if I were in this situation, I would first check to be sure that the 3-prong plug has the same size ground wire as hot wire. It most likely does. I would take out the 3 prong plug and replace it with a 4 prong plug then run at least a 10 guage wire from the neutral terminal to either the electrical panel or a ground rod. The addition of the ground rod is what lets the utility company get away with only one neutral wire going to the house. A new ground rod at the plug provides the same security that the rest of the house has. This wire does not have to be insulated any more than the one from the panel to the existing ground rod. A ground rod can be added near the outlet by drilling a hole in the floor and driving the rod in. Follow the wiring instructions from GlenLever and you will be good.

GlennLever wrote:
I have been using my welding outlet in the garage to power the motor home for over a year.

It is true that the three prong outlet has no neutral, it contains two hot leads and a ground, 110 on one led to the ground and 110 on the other leg to the ground. There is 220 cross the two hot legs.




The four prong plug contains two hot leads, one ground, and one neutral.

It also has 220 potential across the two hot leads.





The different between the two is that the four prong contains the neutral.

What most people forget is the natural and ground are connected together on the same buss bar in the breaker box.



Note in this circuit breaker panel that the white netrual wire and the bare ground wire are connected to the same buss bars.



So if the natural and ground are connected together at the plug it will work just fine. It is not code. Every electrician will tell you not to do it, but it works.

What I did is I went to Home Depot and purchased a drier cord, and a four pin outlet that fits the Motor Home. I wired the plug and wire to the outlet, one outside wire (one leg) to one hot prong, the other outside wire to the other hot prong (other leg)and connected the ground and neutral together.

VERY GOOD! Right on the money.

Go look at the transformer on the utility pole and see how many wires are coming out of the transformer and how many are not for a typical 240 Volt home/shop hook up.

You really want to get dangerous, run one hot wire, sink a copper rod into the ground deep enough to create a good ground and connect your ground wire, and you will have a 120 Volt circuit. BUT DON'T DO IT!

Anyone want to discuss ground loops? Lightning induction?

It has been a LONG time since I slept in a Holiday Inn Express!

Neutral has to be able to carry the full current of either leg and do it for hours if needed.

Ground needs to carry more than the leg breaker rating, for less than 1/2 second

Current causes the wire to heat,, but it takes both current and TIME for it to get hot (If you do not believe me ask your wife..The iron she uses on our shirt does not get "instantly hot" when she turns it on) so the ground can be smaller because in theory it should NEVER carry current, and if id does it only needs to haul the load for ..Well CLICK and no current.

Ivylog wrote:
Like GlennLever (I'll bet) we are over 60 and remember when 120V only used two wires and 240V used three. Like him I have an adapter that lets me hook into my brothers 3 wire 240V welder outlet to power my MH. We can lead you to the water but we cannot make you drink. For those that cannot understand that the ground and neutral are one and the same at the circuit breaker box and cannot look outside and see that there are only three wires coming into your house; I guess you could run a neutral wire out of the 4 outlet box and plug it into your standard three prong 120V outlet so the neutral is still separated (until it gets to the circuit breaker) box if this will make things right.
I wonder how much liability insurance this guy has for selling this adapter?

Some of us, even though we are of the older generation, are still observant enough to not only see the three wires, two hots and a neutral, in an overhead service drop to a residence, but we also see the fourth safety ground wire connected typically at the meter box to a copper ground rod and continued on to the main panel ground bus.

So you can make it work, with a DIY adapter... using the ground for a neutral
IF YOUR installed ground wire is large enough
That does not make it a safe practice, or something to describe on this board
What you are describing, is an emergency/disaster make do situation, because lives depend on having power
Because you have to and it might work
That is not something to post here

I realize this is old, and I'm not licensed, but I wanted to clarify what y'all are saying. The point most people miss is the word "branch". I have a 3 prong 50 amp welder circuit in my garage. I installed it, and I know that it goes directly from the outlet to the panel. I can add an adapter to that to connect to an RV with no problem. If I had not installed it, I may not be able to use it, and here's why.

Under normal circumstances, the complete circuit is between the two hot wires, and there is no current on my ground wire. In the event of a short, the current takes the ground wire and goes right to the breaker. But, if I had another appliance on this "branch" that was also connected to that ground wire, the current would go there first. If you happened to be touching something on that appliance that made you the path of least resistance, you would get shocked.

Expand this to the 4 wire; the neutral is always carrying the 120v half of the current. It can't ever be connected to a ground on another appliance because it risks someone else being the path of least resistance. As you say, it is connected to ground at the breaker box, but there's no chance in a properly installed system of anything further out on that ground wire being less resistance than the directly connected ground rod in the panel. So if the current manages to make it all the way back to the breaker box, it won't travel back up to an appliance and energize it. So if anything else shares that "branch", they share ground wires, which won't normally carry current, and they share neutrals and hots, which are expected to carry current. All of the appliances and such are designed to isolate you from the wires expected to carry current, but not from the ones that aren't expected to.

So, back to my garage circuit, I can use it (provided my ground wire is big enough, which I don't recall for certain) because I know that the ground wire is NOT shared by anything else on the branch. But if you have a connection in your garage that you didn't install, it MAY be connected to ground on something else, and could be a danger if you adapt it to 4 prong for the RV.