30amp 50amp Revisited

[cuts_up]

Our mh has a cord and plug for hooking up to 30amp shore power.  The mh is a 1993 and I'm pretty sure that the cord and plug are original equipment.  When we bought it the seller told us we can run only one a/c at a time while plugged into shore power, and showed us the switch for choosing which a/c we will run.  When we were connected to a 30amp service we weren't sure about the load so we turned off the one a/c before using the microwave, I don't know if we had to do that or not.  With the generator running we can run both a/c's.  In order to run both a/c's hooked up to shore power do I only need an adapter to plug our 30amp setup into a 50amp outlet and get the full benefit of the available 50 amps?  I read in another post about a 30amp or 50amp main breaker.  Do I need to check out what I have before trying to plug into more than 30 amps?  Does the generator power pass through that same main breaker?

We stayed at a state park that had 1-30amp outlet and 2-20amp outlets.  Is it possible (safe) to use a splitter to bring both 30amps and 20amps in at the same time if the mh will handle 50 amps?

Sorry if this is a repeat, but I've searched posts and the library and I didn't find answers to my questions.

 

[Ned]

Plugging your 30A power cord into a 50A outlet via an adapter will not get you 50A power as the main circuit breaker in your load center is 30A.

No, you cannot use the 30A and 20A outlets to get 50A power to your RV.  It's 30A at most, again because the CB in the load center is 30A.

If you had both A/C units running on the generator, you were just lucky in that both compressors didn't start at the same time.  That would have tripped your 30A main breaker in your load center.

 

[Jim Godward]

Ned,

Our old SeaBreeze was wired like this one.  On shore power, one AC; on generator, 2 AC.  I did some rewiring like the other thread indicates and with a second 20 amp extension cord, I coud run both ACs, one on the 20 amp circuit, the other on the 30 amp circuit.  Got to watch the wiring and really be sure of what you are doing!  VBG

 

[Ned]

Then the generator must have been a 4.5KW unit or so to run both A/C units at the same time.  That's more than the 30A shore power can supply and must have had a controller of sorts to handle it.

Yes, you can use a completely separate 20A circuit to power the second A/C unit, but the original question was asking about combining the 30A and 20A outlets to supply 50A to the RV.  That won't work.

 

[Jim Godward]

Ned,

That's what I get for not reading the whole thread!!

You are right that will not do it!!

yes it was a 4.5KW genny

 

[Bob Buchanan]

Ned,

Our old SeaBreeze was wired like this one.? On shore power, one AC; on generator, 2 AC.? I did some rewiring like the other thread indicates and with a second 20 amp extension cord, I coud run both ACs, one on the 20 amp circuit, the other on the 30 amp circuit.? Got to watch the wiring and really be sure of what you are doing!? VBG

My new used rig is 30amp w/2 airs -- and set up to only run both airs on genset power. Ned, I have done that for extended periods, plus done microwaving with no problems. Surely both compressors at least once started at the same time. However, you make a good point that I will check out. Like you and I though -- it isn't the running that is difficult, it's getting started that uses more energy then we have available.

On the use of splitters. I became familiar with them while at the CalExpo park in Sacramento. Seems that on some posts w/20 and 30 outlets, together did not equal 50amp. The 20 was coming from the 30 line in. So if a splitter is tried, it would blow the entire row of posts. This was posted in the office -- but many with 50amp rigs paying for 30 amp sites continually tried to steal extra power.

In this park, the State police were the ones that knocked on the door of the culprit user.

Anyway, my suggestion would be to get the OK from the park office if using a splitter. Seems only fair to the park - especially if they are having trouble with the extremely high costs of electric such as is the case in CA and AZ. Also, if you are not sure of how the post is wired. ?Parks by law cannot make a profit from the electricity used by an RVer. They can only pass on the cost "to" the RVer. That becomes very difficult on over night stays, for example, when trying to keep their nightly fees as competitive as possible - if someone is paying for a 30amp site and using 50amp to run 2 airs plus whatever.

 

[Ned]

Seems that on some posts w/20 and 30 outlets, together did not equal 50amp. The 20 was coming from the 30 line in. So if a splitter is tried, it would blow the entire row of posts.

That was my point, you can't know how the pedestal is wired, and run a big risk in trying to combine the two outlets in the hope of getting something for nothing.

 

[Tom]

In the boating world we use something called a Smart-Y adapter to connect two 30A posts to a 50A cord. In this case, since we need 240V, the two posts/receptacles need to be on different legs. The 'Smart' name comes from the fact that the Y prevents power from being passed to any pins unless two separate legs are present and powered. When it's not obvious whether posts/receptacles are on the same or different legs, I'll sometimes check them out with a multimeter. This isn't always easy if the posts are 30-50 feet apart.

For clarification, in these cases, we're not trying to get more power than we paid for (I'll often talk to the office or one of their workers), but some of our appliances and the heat/air systems are 240V. When two legs aren't available, I have an adapter that I made to power one leg in conjunction with some panel rewiring and I also practice load management (aka preventing my other half from switching too many 110V things on at the same time).

 

[Ned]

A multimeter won't tell you if the two circuits are on different legs.  You need something like the Smart-Y with control circuitry to prevent a problem.  Even so, combining a 30A and a 20A circuit will give 50A, if wired correctly, but RV 50A service is really 100A, 50A on each leg.  And the RV load center is only 30A so just feeding 50A to it won't help one bit.

 

[Tom]

A multimeter won't tell you if the two circuits are on different legs.

Eh? If they're on different legs, I'd read 240V between the hot pins. If not, I'd read 0V. Or, as we used to do it in the old days, hook a pair or wires to some unsuspecting soul and estimate the voltage from how high he jumps.

..... feeding 50A to it won't help one bit.

Didn't suggest it would. I was merely responding to the comment that "you can't know how a pedestal is wired". Yes, having the Smart-Y tell me is the best way, but sometimes it's not practical. That's when I get out the multimeter.

BTW when a co-worker accidentally touched a 3KV bus, it launched him across the substation. That gave us a new calibration point for measuring voltage  ;D

 

[Ned]

Ok, I was thinking about measuring each outlet separately, not in combination.  Your method is correct.

The original question was about combining a 30A and 20A outlet to supply 50A, and my reply was that it wouldn't work, for all the reasons discussed.  It wasn't in response to anything you wrote.

 

[Tom]

It wasn't in response to anything you wrote.

OK, thanks for clarification.

BTW you wanna be the audience participant next time I demo the "how high, how many volts" trick? It's a lot of fun for the audience, but not as much fun for the participant. We could rename it to "how high, how many legs".

A more civilized, albeit equally imprecise, method we used was a "test light" comprised of a couple of 240V bulbs in a wooden box with a couple of leads/probes. If the lamps shone brightly, it was 240V. If they were dim, it was 120V. Usually more convenient than trying to use one of those large, heavy, relatively fragile, analog multimeters of yesteryear, especially in a hostile environment. But, if neither bulb lit, it was time for the wet finger test.

 

[Ned]

Thanks, I'll pass, but may have some suggestions for volunteers   I do know from experience that high voltage DC can cause severe enough muscle contractions to propel a body across a basement.  After that, AC is easy