Dryer receptacle adapter

[M2HB]

I have a spare NEMA 10-30 receptacle in our new house. As I understand it this is two 30 amp 120 volt lines combined into one 240 volt circuit. Is this correct? Is it safe or feasible to fabricate an adapter to split this into two 120 volt circuits and connect to the two 120 volt legs of an RV 50 amp circuit? I am having an electrician install the proper 50 amp outlet at the new house next week so I will not actually be using such an adapter but I wonder if it would be useful if I found myself in a situation where I needed more power than a normal household 15 or 20 amp plug could provide.

[mahon1993]

Do not plug anything with any kind of adaptor into that outlet unless you are sure of what you got. Chances are it is a 240 volt dryer / welder outlet. Plugging a RV into it means instant expensive smoke. Have an electrican install the proper 50 amp rv plug for you.
Greg

[wa8yxm]

IS it feasible: Non sufficient data.. (I will explain)

Is it reasonable and proper: NO. in most cases.

Do I recommend it: NO.

Do I know how to do it.. Well, if it is possible (And I'm not saying it is)

Danger: There is still a company, present in every city or township or county, that makes house calls.. it's called Company __ of the Fire Department. And the danger is they may come a calling if you make an adapter.. Which is why I'm not going to tell you how to do it.

The problem: To run a proper 30 amp circuit you need fairly heavy wire, like 6 or 8 ga for any length of run, minimum 10ga for short runs. The problem is that the cable to that outlet is 3 wire.. (As you can deduce from the fact there are 3 slots in the outlet) now the two HOT leads, will be the right size, but the 3rd wire (Neutral) may be considerably smaller, since it is designed to carry current for only a brief period (Just long enough to make the breaker go CLICK)

Or to carry far less current.

If you plug in an RV with an adapter. You can easily overload this neutral wire unless your loads are properly balanced.

Second.. You will only be able to connect 3 wires, This leaves the safety ground floating, Normally one would think this is not a problem.. HOWEVER I can all but guarantee you will end up with the chassis at considerable voltage above ground unless you address this.

THUS.. I do not recommend trying it.

IF you pull a proper 4-wire cable, you could use a 50 amp RV outlet and without changing the breakers slap a label (Brother P-Touch is great for this) "30 amp limit"

That... Would be safe, IT would be better, You would run no danger of a neutral overload, and the safety ground would be there... The only danger is Eva Gabor syndrom (Turning 40 amps of stuff on a 30 amp leg and getting the CLICK of darkness,,, From the TV show Green Acres)

[bluepill]

Lack of a proper and sufficient ground with the NEMA 10 30 configuration is the killer. Pun Intended.

[GaryKD]

Hi M2HB,
The technical explanation is already posted. For me, I wouldn't touch this. If you want an outlet for the coach, do it correctly from the beginning. None of the parts are expensive.

[GWinger]

Quote:

Originally Posted by wa8yxm IS it feasible: Non sufficient data.. (I will explain) Is it reasonable and proper: NO. in most cases. Do I recommend it: NO. Do I know how to do it.. Well, if it is possible (And I'm not saying it is) Danger: There is still a company, present in every city or township or county, that makes house calls.. it's called Company __ of the Fire Department. And the danger is they may come a calling if you make an adapter.. Which is why I'm not going to tell you how to do it. The problem: To run a proper 30 amp circuit you need fairly heavy wire, like 6 or 8 ga for any length of run, minimum 10ga for short runs. The problem is that the cable to that outlet is 3 wire.. (As you can deduce from the fact there are 3 slots in the outlet) now the two HOT leads, will be the right size, but the 3rd wire (Neutral) may be considerably smaller, since it is designed to carry current for only a brief period (Just long enough to make the breaker go CLICK) Or to carry far less current. If you plug in an RV with an adapter. You can easily overload this neutral wire unless your loads are properly balanced. Second.. You will only be able to connect 3 wires, This leaves the safety ground floating, Normally one would think this is not a problem.. HOWEVER I can all but guarantee you will end up with the chassis at considerable voltage above ground unless you address this. THUS.. I do not recommend trying it. IF you pull a proper 4-wire cable, you could use a 50 amp RV outlet and without changing the breakers slap a label (Brother P-Touch is great for this) "30 amp limit" That... Would be safe, IT would be better, You would run no danger of a neutral overload, and the safety ground would be there... The only danger is Eva Gabor syndrom (Turning 40 amps of stuff on a 30 amp leg and getting the CLICK of darkness,,, From the TV show Green Acres)

wa8xym,
Not to dispute anything you said, but to clarify, your paragraph beginning with, "The Problem,..."
The NEC says 10 gauge copper wiring is SAFE for a 30 amp circuit. The only reason to increase it to 6 or 8 would be for a very long run. It helps to prevent voltage drop along the longer runs. As far as the neutral being smaller (#10) that isn't a problem a when the voltage between the other two legs is 240vac, the neutral carries only the 'unbalance' current.
Meaning if your pulling say 12 amps on one leg and 10amps on the other, the neutral is carrying only 2amps. On a circuit protected with a 30amp circuit breaker, the current on the neutral is never more than 30 amps, and most often, less. The danger in tapping off a three-wire circuit is that while you have a neutral, you have no Ground. The neutral normally carries current. The Ground is designed to carry only Fault current, which normally would occur when something shorts out.

The power for a 50amp circuit to an RV should NEVER originate from the same 120volt power phase. Which can happen when someone who doesn't understand electricity trys to adapt a circuit to an RV from a dryer or range home outlet.
GWinger

[Tallyrver]

I had a 50 amp installed at my driveway , a friend was going to do it .He thought it was the same plug as a drier...I did a little research. There could have been a visit from the big red truck if he had done it the way he wanted. I did the labor and had another electrician check it for me.

This link has some great information ,for you and the person that is doing the work .

Wayne

RV Electric

[wa8yxm]

I fully agree Winger.. I like to use oversize wire, (Safer, lower voltage drop, etc) in case you wonder.

I did say without a ground I can virtually guarantee a hot chassis (Voltage present) didn't I.. Thought I did.

In short don't do it.

[vermilye]

Although the neutral does carry the difference between the hots, in the case of RVs & some other types of loads, there is a good possibility that the load will not be balanced. Because of this it is important (and required by NEC) that the neutral be full sized.

I agree that even if there was a full sized neutral, because a 3 pole dryer receptacle combines the ground & neutral, there is no way it can be safely used to power a RV. At a minimum, you will be putting the neutral voltage on the frame of the RV. At the worst, you will annoy plumbers working on copper piping in the house & set up a condition that might result in a shock from a stream of water.