Using Dryer's NEMA 14-30 outlet for RV shore power

Hey folks,

UPDATE:
Skip all the banter and jump to the CURRENT PLAN using this link!

Original Post:
I've been reading lots of posts about using dryer hookups for RV shore power at home and lots of them are outdated (using the older NEMA 10-30 outlets). This question is about the newer NEMA 14-30 hookups.

(Edited to add this DISCLAIMER: For the sake of clarity, I am a degreed electrical engineer with ~20yrs experience and have worked around electricity my entire life. I have done plenty of wiring jobs at my own house and at the houses of friends and family. I understand electricity and the risks involved significantly well. I do plenty of electrical work, but do draw the line at installation of a new subpanel or main service entrance. :) I believe this thread is entirely useful for others who may wish to install a NEMA 14-50 outlet in their garage (whether for their RV or their Tesla). But, if you are not qualified to work on electrical systems, PLEASE do not take this thread as a suggestion that such a job is easy and without significant risk. I will not, nor will any other contributor to this thread, be responsible for anything you do as a result of this thread.)

For reference..

OLD style:
Link: Wikipedia NEMA 10 Style
Example:

NEW style:
Link: Wikipedia NEMA 14 Style
Example:

My house (build circa 2007) has the newer style NEMA 14-30 connector. When I put a multi-meter on it, it measures like this:

That seems to me equivalent to the necessary 50A hookup on an RV (albeit with only 30A's "actual"):

It also seems to me that I could use a 2-phase (DPDT) 30A switch to switch between my dryer outlet (inside) and a RV outlet (garage), using a switch such as the Leviton 1288 to switch power between the dryer and the garage outlets.

Leviton 1288:

However, I read over and over about people frying their RV trying to hook up shore power various ways from their house. SO I wanted to try and clarify what I think would work and get feedback.

It seems to me that I can use my dryer dual-30A hookup to power a 50A RV hookup with the stipulation that it will be limited to 30A per leg at the breaker box.

To be clear, our goals would be:

Park the RV in front of the house before/after trip for loading/unloading
Have Lights, A/C, and fridge running while loading/unloading
*NOT* planning on daily living use (microwave, etc)

It would seem to me that this circuit would be able to do the job.

My plan currently is:

Turn off dryer circuit breaker (safety first!)
Disconnect existing circuit from dryer outlet
Connect circuit from breaker to a DPDT switch such as the Leviton 1288 (linked above)
Connect one set of switch outputs to Dryer outlet
Connect second set of switch outputs to Garage RV outlet

Lastly, I want to again point out that this scenario would only supply 30A to each 120V leg even though we would be using a 14-50 style 50A RV hookup plug. This limitation comes from the breaker box itself. I cannot replace the breaker with a 50A because it would involve pulling new 50A wiring, and might violate dryer safety.

So, ..... thoughts?

cheers,
..dane

1320Fastback
Explorer
Sep 08, 2019
I have a unused 30A 3-wire outlet in our basement access tunnel which is conveniently very close to the driveway and my workshop. Over the years I have made many extension cords or adapters to plug various things into it and as long as you think about the wiring it's a non-issue.
Old-Biscuit
Explorer III
Sep 08, 2019
cavie wrote:
audiodane wrote:
cavie wrote:
Please lay down the tools and back away. Please refrain from doing any electric work.

I'm sorry, @cavie, but what is your reasoning? Because *you* are nervous to do electrical work? Please understand I mean no disrespect, but you shouldn't project your own uncertainty onto others without at least justifying your answer.

I am a degreed electrical engineer with 20yrs experience and have worked around electricity my entire life and have done plenty of wiring jobs at my own house and at the houses of friends and family. I understand electricity and the risks involved significantly well. I do plenty of electrical work, but do draw the line at installation of a new subpanel or main service entrance. :) Granted, I did not put that information in my OP and will go do that for future thread readers.

EDIT: OP updated to add disclaimer. :)

cheers,
..dane

If I was afraid of electricity I would not survived being a 45 year Master Electrician, Building Inspector, and present owner of two Electric Companies. Have a nice day.;)

At least have the courtesy to post your reasoning as you are the one that posted the 'step away' comment.
Why not be informative and use your 45 yr Master Electricain knowledge to educate vs just making snide remarks.
OP asked for your reasoning....provide it!
time2roll
Nomad
Sep 08, 2019
audiodane wrote:
wnjj wrote:
Are your 240V breakers already doubled up? Depending upon the breaker and panel you may be able to swap your dryer breaker for a double one like this.

They even make those with a 50 and 30 in the same breaker (here).

Whoa!! Thanks @wnjj! I've never seen that second one before. I could drop a short 50A receptical just below the panel that way! That would be SOOOOO much cleaner, meet code, AND not have to fiddle with the dryer switch.... WOW. BEST. POST. EVER. Thank you!

...

So this little booger could allow me to do this:

Click For Full-Size Image.

Perfect
JRscooby
Explorer II
Sep 08, 2019
ScottG wrote:

This thread may not apply, but often I see what I think are real simple electrical questions asked. I wonder if because the person know so little, must ask the question, if "Put down the tools" would not be the best answer?

Like you say, this thread doesn't apply.

Unless I missed it, until after the "put tool" the only thing I was sure of about the OP was he could move pictures on a site to another. I can understand the OP not like being told, if he already knew what was what. Bell, start telling me how I should shift my Super 10 might wad my shorts, if you did not explain you designed the transmission.
After the "offensive remark" we are told the OP should know everything about it. Now sometimes I will ask a question I know the answer to in hope of teaching, but who is the OP teaching? If just wanting to have the discussion for entertainment, fine. If wanting to learn things?
DrewE
Explorer II
Sep 08, 2019
larry cad wrote:

I don't agree with you. No reason why the 50 amp receptacle cannot be wired from a 30 amp circuit. I will concede IF you can point out the specific code section where this is stated. Typical residential duplex receptacles come in 15 and 20 amp configurations and are typically and legally used in both 15 and 20 amp circuits.

See 210.20B(3): "Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.20(B)(3) ....", followed by a few exceptions that would not apply.

The table says that for 30A circuits, only 30A receptacles are permitted. (For 20A circuits, either 15 or 20A receptacles are permitted. For 15A circuits, though, 20A receptacles are not permitted.)

I do agree that there is no immediate safety issue with putting a 50A receptacle on a 30A circuit; it's obviously more than capable of handling the current that it could carry. I also don't claim that the code is entirely self-evident or perfectly logical. Presumably the idea is to prevent excessive tripping of breakers or running the undersized circuit at the very edge of its capacity all the time or something similar (and maybe also to encourage the makers of equipment to provide appropriately sized power cords and plugs, rather than oversizing them for "convenience" or other reasons).
audiodane
Explorer
Sep 08, 2019
Old-Biscuit wrote:
You stated you were going to use a NEMA 14-30 receptacle.....which is for 30A so not sure why the 50A discussion :H

Dual 30A CBs (or even the 30A/50A combo CBs) would require pulling new/additional wires

EE hat on and back to the drawing board

Ha! You made me have to go back and re-read my OP. Nice work!

But no, I was stating that I had a NEMA 14-30 outlet for my dryer, which gives me 2x 120V @30A circuits, that I could then run into a 14-50 RV outlet (with the limitations of the breaker @ 30A each)

I admit that perhaps I wasn't the most clear though. Once a solution is settled upon, I'll go back and update the OP again to point to a final solution post on a later page...

cheers,
..dane
audiodane
Explorer
Sep 08, 2019
stevemorris wrote:
yes the drier outlet/circuit can be used for a 50 amp rv, so can the kitchen stove circuit

BUT, in ontario, canada and probably other provinces, it is against the electrical code. both the drier and stove outlets must be dedicated circuits and the electrical code specifically states that other outlets on those circuits are not permitted. a switch in that drier circuit, even rated for that heavy current, is likely not permitted either
i have seen a similar situation, a guy i know wired a 30 amp, 240 v circuit into his garage using the central air circuit, thinking he would never heat his garage while using his central ac unit. good assumption BUT later somebody else could use that 30 amp plug for something else(big power tools for example) while the ac was on
my electrical knowledge is also extensive as is my knowledge of the electrical codes and in ontario this is NOT allowed

Thanks @stevemorris for that explanation of code. I totally agree that there is risk involved in a 50A outlet on a 30A circuit, or both the dryer and RV hookup at the same time. My original idea of a switch was at least to attempt to solve the easier of the two problems (only one at a time).

I think the later solution to change some of the breakers and just work in a double 50A breaker is a far simpler solution and is currently my preferred choice. Gets rid of the switch, protects against future dummies (maybe even a forgetful self!), meets code, and can be touted as "supporting the latest in-home Tesla charging station" with a fully-powered 14-50 outlet.

..dane
audiodane
Explorer
Sep 08, 2019
JRscooby wrote:
I'm just a dumb truck driver. I would get the heavy wire, run thru walls as you plan. Mount and wire a 50 AMP RV outlet where handy. On the other end, put a drier plug. Could only plug in one at a time, so no overload issue. Inspector coming? Hide the plug.

lol thanks @JRscooby. I wouldn't call a truck driver "dumb" by any means (unless you're that one that swerves back and forth and cuts off drivers with a fully loaded rig that I see on the interstates from time to time -- in which case we need to have a come-to-Jesus talk! :D ).

Actually your idea is what I was thinking FIRST. However the dryer's inside, and I was wanting something on the garage side. A big hole in the wall for a pass-through cable would not be good for heat-insulation, nor for bugs. So my next thought was a switch between the two outlets, essentially accomplishing the same goal as what you describe, but without having a hole in the wall to pass a plug through. :D

I think the "double up on some breakers and add your 50A double breaker with an outlet below the panel" is the best idea, and is most likely what I'll look to do ... BUT -- I did have the SAME thought as you first! Keep it Simple, right? :D
audiodane
Explorer
Sep 08, 2019
wnjj wrote:
One word of caution here before you buy everything: my panel only allows doubles in the lower section of the panel. Since I needed more room in order to install a normal sized arc fault breaker, I put one like that in the bottom and put the arc fault and another up top. That said, they do make specific breakers that allow doubling in the top but I’m not sure if they come in mixed sizes. What you could do if you can only fine 2 the same is combine two existing ones, freeing up a spot for a 50.

The way you can tell is by the depth of the slot in the back of the breaker. The fins in the top of panel are solid and the ones that allow doubling have a fork. The deeper doubles are much more expensive, presumably to prevent common use of them up top.

If you do need to rearrange anything in the panel, you can splice the wires with wire nuts if needed since the panel also meets the requirements of a junction box.

Info here: http://m.startribune.com/how-to-know-when-tandem-circuit-breakers-can-be-used-aka-cheater-breakers/140688183/

Thank you AGAIN, @wnjj. i will pull the cover off the panel and have a look. I wonder if I need to actually remove a breaker to tell. I'll check the links you gave before I get started.

I suppose I could very easily rearrange a few of the 15A circuits in there and really open up a spot anywhere to put in a double 50A breaker... If I'm doing panel work anyway, it doesn't really matter at that point.
Learjet
Explorer
Sep 08, 2019
As I said in post #2 do it right and add the circuit. The double 240 or if you have some single 120 CBs you can get those in double to make space for another standard 240 breaker. :)