Can I plug my 50amp cord from my class A into a dryer outlet?

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.

Kirk

Well-known member
Joined
Oct 30, 2005
Posts
4,111
Location
Full-time , Escapee
But I bet I am not the first to make that mistake!
You are not even close to first and no offence at all. What you probably don't know is that my last name is one that probably the vast majority of people add an S to and since I don't have a middle name, some ever think that my last name is Kirkwood and want to know my first! :LOL:
 
Last edited:

Pedro Dog

Well-known member
Joined
Jul 9, 2022
Posts
559
Location
South Shores, CA
Man you are hard headed;)

Take a 12-volt car engine starter for an example. One side is hot, the other side is grounded.
There is no ground in a car electrical system. The rubber tires isolate the vehicle from earth ground. What you have is a closed loop 12 VDC system, one side is +12VDC (Anode) referenced to to the Cathode which in this case is basically floating.

If the starter motor itself is not grounded at the case, the current in the grounded negative wire is the exact same as in the positive starter wire and that is a lot of current.
Your analogy is flawed, the return path for the current through the load (starter) back to the battery (-) is not a ground wire, it is analogous to the neutral in the AC system.
 

Pedro Dog

Well-known member
Joined
Jul 9, 2022
Posts
559
Location
South Shores, CA
The term "ground" in a car system is a misnomer used by people to describe the lowest voltage potential in the car 12VDC system. It is the path for electrons to travel back to the energy source (return) to the battery.
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
8,271
Location
Auburn, CA or Reno, NV
It is the path for electrons to travel back to the energy source (return) to the battery.
It's a very commonly used term to ground a wire to an RV or auto frame. I have even heard the frames referred to as an "earth ground" (mostly British). That is where I would draw the line. To me that is a ground, but not an earth ground.

Reminds me of the EV term "regenerative braking". My Tesla has NONE at all. Absolutely Zero, even at the highest regen setting. My Chevy Bolt has a lot of it, added to the "regenerative deceleration" which my Tesla has a lot of.

But it will probably take more than you and me to get people to use the correct terms when the incorrect terms are in wide accepted use.

But even the earth can qualify for a return to the source. Think of how a GFI works with a human body between the hot (black wire) and earth. That is simply a path between the hot black wire and ground. That current is then missing from the white wire (very slightly lower) and trips the GFI as the differential amplifier detects the current difference between the black and white. They no longer match so it trips. But the earth is completing the path back to the source which is often the case even with a TRUE earth ground.

The earth can make a reasonably good conductor to complete some paths.

-Don- Phoenix, OR
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
8,271
Location
Auburn, CA or Reno, NV
And that is the reason that there no point in any of us responding.
So you're saying that is the case? Reread my message. It is saying that the tech people here probably know more about this issue than the 20 people at NFPA. If you guys cannot explain it, I will continue to believe it is NOT a safety issue at all, regardless of what the 20 people at NFPA say. AFAIK, those people at NFPA never explained it, but if they did, I would love to read it!

People here are probably better qualified than they are!

If somebody can explain it, I will be very quick to agree, if it even makes a little sense. But so far, the best techs in this forum have not even tried. Why?

Are the more tech people here only agreeing with the NFPA because those 20 did and for no technical reason at all?

-Don- Phoenix, OR
 

NY_Dutch

Well-known member
Joined
Nov 22, 2010
Posts
8,127
Location
Where our wheels take us!
If I were on it, I would have to straighten out the other 19 people! ;)

But are you saying of all the electricians in this forum, and other technical people, like you, Mark, Kirt, Lou and others (and myself) have no idea how to answer such a very simple question about the safety difference between the 3 and four prong dryer outlet? I need to go talk to that committee to go find out?

If that's the case, I am already decided that the three-prong is equally as safe as the four-prong. And I am betting my life with it because BOTH of my homes have the three-prong.

-Don- Phoenix, OR
With the 3-prong outlet it only takes a one wire failure, the combined ground and neutral, to create a potentially hazardous condition. With the 4-prong outlet, both wires would have to fail.
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
8,271
Location
Auburn, CA or Reno, NV
With the 3-prong outlet it only takes a one wire failure, the combined ground and neutral, to create a potentially hazardous condition. With the 4-prong outlet, both wires would have to fail.
I kinda thought that could have been it, and I think you have it.

IOW, It's all about a possible failure condition, not the normal condition.

But I have to question just a little how well a neutral works as a ground. Certainly better than nothing especially if balanced properly on each of the 120 VAC lines.

-Don- Phoenix, OR
 

Pedro Dog

Well-known member
Joined
Jul 9, 2022
Posts
559
Location
South Shores, CA
The neutral is the path for the current to travel back to it's source, the power station. It does not work as a ground. When the neutral and ground wire are bonded together to a copper rod driven into the earth at the service panel, it's to provide a reference. The electrons still go back to the power station, not to the earth.
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
8,271
Location
Auburn, CA or Reno, NV
The neutral is the path for the current to travel back to it's source, the power station. It does not work as a ground. When the neutral and ground wire are bonded together to a copper rod driven into the earth at the service panel, it's to provide a reference. The electrons still go back to the power station, not to the earth.
But do you consider the four prong safer than the three prong? If you do, please explain why.

And reference for what? I think of the neutral as being no more than the center-tap of the 240 VAC transformer that feeds a house. IOW, a way to get two 120 VAC lines as well as one 240 VAC line. Regardless if the neutral is grounded or not.

-Don- Phoenix, OR
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
8,271
Location
Auburn, CA or Reno, NV
I was just thinking about this, and I think NY-Dutch is perhaps close enough.

On the 3-prong, we can easily lose both ground and neutral at the same time. But let's say the neutral only goes open on a 4-prong. You still have the dryer frame at earth ground with all that 240 VAC safely floating around inside the dryer.

-Don- Phoenix, OR
 

Ex-Calif

Well-known member
Joined
May 15, 2020
Posts
3,813
Location
NorthCentral Florida
I was just thinking about this, and I think NY-Dutch is perhaps close enough.

On the 3-prong, we can easily lose both ground and neutral at the same time. But let's say the neutral only goes open on a 4-prong. You still have the dryer frame at earth ground with all that 240 VAC safely floating around inside the dryer.

-Don- Phoenix, OR

240VAC doesn't just float around.

The potential needs to find it's way back to the source. In the case of a WYE transformer you have 2 X 120V legs and a neutral.

The ground is intended for a path like a lightning strike. It is also a path of least resistance back to the source should the neutral leg fail.

I suggest you watch this video all the way through. It made a lot of things clear for me when I went to wire up my mobile home.


Note that when he demonstrates the potential on the neutral and ground legs he purposefully makes an imbalance load.

You've stated over and over that a 50amp service is 2 X 120V. It's actually a misnomer because at the pedestal it is 2 hot legs, a neutral and a ground.

RV loads can get extremely imbalanced depending on what is running off of each 120V leg. If the A/Cs are split and only one is running you could have a 15amp split right there.

I'll back up NY-Dutch on the 4-prong as you have both a neutral path and an EGC path.
 

NY_Dutch

Well-known member
Joined
Nov 22, 2010
Posts
8,127
Location
Where our wheels take us!
240VAC doesn't just float around.

The potential needs to find it's way back to the source. In the case of a WYE transformer you have 2 X 120V legs and a neutral.

The ground is intended for a path like a lightning strike. It is also a path of least resistance back to the source should the neutral leg fail.

I suggest you watch this video all the way through. It made a lot of things clear for me when I went to wire up my mobile home.


Note that when he demonstrates the potential on the neutral and ground legs he purposefully makes an imbalance load.

You've stated over and over that a 50amp service is 2 X 120V. It's actually a misnomer because at the pedestal it is 2 hot legs, a neutral and a ground.

RV loads can get extremely imbalanced depending on what is running off of each 120V leg. If the A/Cs are split and only one is running you could have a 15amp split right there.

I'll back up NY-Dutch on the 4-prong as you have both a neutral path and an EGC path.
Thanks for the informative video! To relate it a bit more to our RV's, we should note that an RV service panel is a sub-panel when connected to shorepower, with the neutral and ground separate as shown. The park stanchion is also a sub-panel. If anyone really wants to read all the details regarding acceptable RV wiring, NFPA 70 (NEC) Article 551 is the go to source.
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
8,271
Location
Auburn, CA or Reno, NV
You've stated over and over that a 50amp service is 2 X 120V. It's actually a misnomer because at the pedestal it is 2 hot legs, a neutral and a ground.
I don't recall saying that, but I don't see what you're saying or what the difference is. That seems accurate to me anyway, for the 50-amp service, but not for the 30-amp. 240 VAC center-tapped at a transformer secondary becomes two 120 VAC lines along with 240 VAC. The 240 VAC is usually not used for RVs, such as in this one (50 amp).

30-amp RV service is one hot, one neutral and one ground. No 240 VAC possible.

But it is possible from a 3-prong drier outlet because it uses two hots instead of one. 240, combined ground and neutral and another hot for 240 VAC. So from the dryer outlet, you can get both, 120 VAC and 240 VAC and get a total of 60 amps, unlike a 30-amp RV outlet that is only good for 30 amps total.

There is a reason why the RV plugs will not fit a dryer outlet. They are different voltages.

What I do recall saying is 240 VAC at 50 amps is a 100-amp total at 120 VAC. 50 amps per 120 VAC line or a total of 12KW either way. I have said that a few times here as many do not realize the difference between 30-amp RV service and 50-amp RV service is a total of 70 amps, not 20 amps.

-Don- Phoenix, OR
 

Gary RV_Wizard

Site Team
Joined
Feb 2, 2005
Posts
77,155
Location
West Palm Beach, FL
I am already decided that the three-prong is equally as safe as the four-prong. And I am betting my life with it because BOTH of my homes have the three-prong.
It is if you aren't trying to get 120v service from it. The concern is when the ground lug is used in lieu of a neutral. I'm not arguing that pro or con, but I yield to the experts on the NEC committees who have already made their opinion of it known.
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
8,271
Location
Auburn, CA or Reno, NV
I just watched the video. Soundls like the entire idea of keeping the neutral and ground seperate is the difference of possible current on a gas line when having very unequal loads between each 120 VAC line. Something I would have never thought about.

So perhaps the only issue are the gas lines when having an imbalance between 120 VAC lines. I still must wonder if that has really been known to cause a problem, such as causing a gas line to blow up.

His small amount of stray ground current even with seperate ground and neutral I would guess is because a centertap may not be at an exact center of the house transformer, so even when no load there is a trace of being unbalanced between the 120 VAC lines, even when seperate ground and neutral.

-Don- Phoenix, OR
 

DonTom

Well-known member
Joined
Apr 21, 2005
Posts
8,271
Location
Auburn, CA or Reno, NV
It is if you aren't trying to get 120v service from it.
But I guess I probably am. I think 240 VAC dryers usually have a lot of 120 VAC stuff in them. And if the motor is 120 VAC that is likely to cause a rather large imbalance between the two hots.

Should I be worried about it? ;)

They have been combining the ground and neutral for a very long time before the NEC decided it was not as safe as separating them. I wonder if this change was based on something that really happened, such as a gas explosion and somehow no separate ground was proven to be the cause.

-Don- Phoenix, OR
 

Pedro Dog

Well-known member
Joined
Jul 9, 2022
Posts
559
Location
South Shores, CA
If your house was wired with the 240 VAC 3 prong outlet and your appliance was made with a 240 VAC 3 prong cable, then you are going to be safe. The older applainces tied the ground and neutral together inside the unit.

If however you replace the 3 prong dryer with a newer one with a 4 prong connector, and decide to chop off the 4 prong and replace it with a 3 prong, you have to also modify the dryer to be safe (the neutal and ground are not bonded inside the unit). If you just chop off the 4 and replace it with a 3, you are playing with fire. If a hot shorts to the dryer body, the current has no way to get back to the panel and trip the CB. If you are standing barefoot and touch the dryer when this short is active, it's going to hurt.

The alternative to changing the 4 prong to a 3 prong, is to modify the wall wiring by adding a separate ground wire from the outlet to the service panel (if there isn't one there already)
 

Pedro Dog

Well-known member
Joined
Jul 9, 2022
Posts
559
Location
South Shores, CA
People make too much fuss about the so called imbalance. At a homeowner level the imbalance is not going to cause problems because at a maximum, the current will exceed the CB limit and trip. I think the imbalances tend to be more of a problem for the power companies. I may be wrong on this , but in my mind that is the way it works.
 
Top Bottom