30A and 20A to 50A?

[stevejones]

Our trailer is a 50A trailer with two ACs. We're staying in a park where all I have is a 30A hook up. As I hooked up the dogbone to the cable and to the box I saw the 20A circuit that was also in there and wondered, can you use the 30A circuit and the 20A circuit together to make a 50A circuit or at least be able to run both ACs? Especially since we have Easystarts in both units. Maybe using something like this:

https://www.homedepot.com/p/Camco-50...B&gclsrc=aw.ds

Thoughts? Opinions?

Steve

[richard5933]

Many times the 30-amp and the 20-amp receptacles are fed from the same breaker on the main panel feeding the pedestal. It's a crap shoot - some have done it successfully and others have been waiting till the morning when the maintenance crew is around to resent the breaker on their main panel.

I'd suspect that in older campgrounds or sites without 50-amp service this is more likely to be a problem. Unless I asked and was told it was okay, I'd be leery.

[kscherzi]

Read the third review of this product on the Home Depot website.

[uncle_bob]

Hi

A 50A RV circuit is 50A at 230V. A 30A RV circuit is 30A at 120V. At 120V your 50A circuit is a 100A circuit. If you wanted to make up a "full" 50A circuit, it would take a bit more than three 30A plugs to do the job.

Next up, you would need to get half of the 30A current to be 180 degrees out of phase with the other half. That would give you 230 V between the two hot leads relative to the neutral. Far more importantly, it would mean that the hot currents would cancel running down the neutral wire.

The phase reversal is what lets you get away with a 50A wire / contact on the neutral for a "100A" circuit. Without that "feature" you would melt the contact / fry the wire. Since power goes up as current squared, you have 4X the heat going into a contact or wire at 100A compared to 50A.

50A feeds let you turn everything ( not just the A/C ) on in an AS. Knowing what actually *is* on sometimes is a bit interesting. The converter / charger is pulling something .... who knows how much. The absorption fridge switches over to AC and pulls a couple amps. The A/C's might pull 14A, they easily could pull 18A. None of that counts surge currents at (maybe) 45A per unit.

What gizmo goes to which phase? It's a pretty good bet the A/C's are each on a separate phase. Where the rest goes ... who knows. If you have 20A to one phase and that's the "wrong" one ... you have a problem.

So, can you get away with some sort of lash up? Sure you might. Could it fail in a fairly dramatic fashion? Yup ....

Bob

[Glenritas]

The 50 amp circuit is wired as two 25 amp 120 volt circuits going into your trailer .

The two circuits go to your distribution breaker box and from there to the various circuits in your trailer .

This is why you don’t use the same type outlet as a dryer or stove . That type of outlet is wired as a 220 volt outlet . If you somehow adapt your your power cord to plug into that outlet you will cause major damage to your trailers electrical components .

Now to use both the 20amp and 30amp outlets at the rv park to get 50 amp service good luck getting that into your 50 amp cord .

[richard5933]

Originally Posted by Glenritas

The 50 amp circuit is wired as two 25 amp 120 volt circuits going into your trailer .....

Don't think this is correct. A 50-amp pedestal provides two 50-amp legs at 120v. It also can provide one single circuit of 50 amps at 240v. It's often called 120/240v service for this reason, and most RVs will use it as two separate 50-amp legs.

For comparison:

A 30-amp outlet can provide up to 3,600 watts. Amps x volts = watts, so 30 x 120 = 3,600 watts.

A 50-amp outlet can provide up to 12,00 watts. Amps x volts = watts, so now we have two legs of 50 x 120 = 6,000 for a total of 12,000 watts.

One many pedestals we see nowadays there is a 50-amp, a 30-amp, and a 20-amp outlet which are fed from the main power panel by a double 50-amp breaker. This means that there are two legs of power (L1 & L2), each capable of supplying 50 amps. The 50-amp outlet is supplied by L1 & L2.

The 30-amp breaker and the 20-amp breaker in this pedestal would each be fed by one of the legs, so for instance L1 feeding the 30-amp outlet and L2 feeding the 20-amp outlet.

In this pedestal with 50-amp service you could either fully utilize the 50-amp out OR you can fully utilize both the 30-amp and 20-amp outlets. However, pulling full power from all three outlets would likely result in tripping the breaker feeding the pedestal at the main panel. Very few pedestals are wired with a separate feed for the 30-amp and 20-amp outlets, which is why many campgrounds have rules against using them all together.

Back to our pedestal with only a 30-amp and 20-amp outlet. It's likely fed from the main power panel by a single 30-amp circuit and has only one hot leg. With both the 30-amp and 20-amp outlets pulling from this pedestal like is being described by the OP, it would be possible to attempt to pull more current than the circuit is capable of delivering, either tripping the breaker on the main panel or causing other problems.

[Mollysdad]

Richard nailed it!
People get hung up on 30 amp + 20 amp = 50 amp when in reality, it's the watts that make the wheels go round. 50 amps is TWO 50 amp legs, where as the 30 and 20 amp are ONE leg, so although you can do it and there's dogbones for it you'll still only have half the watts.

[uncle_bob]

Originally Posted by Glenritas

The 50 amp circuit is wired as two 25 amp 120 volt circuits going into your trailer .

The two circuits go to your distribution breaker box and from there to the various circuits in your trailer .

This is why you don’t use the same type outlet as a dryer or stove . That type of outlet is wired as a 220 volt outlet . If you somehow adapt your your power cord to plug into that outlet you will cause major damage to your trailers electrical components .

Now to use both the 20amp and 30amp outlets at the rv park to get 50 amp service good luck getting that into your 50 amp cord .

Hi

Nope

The 50A circuit is a 240V circuit. Each hot leg it 120V to the neutral. You get 50A at 120V off of each leg. Take a look at the AC panel in your trailer or the panel on the post at the campground. On either one you will see a dual 50A breaker controlling the circuit.

Indeed pulling 100A at 120V is unlikely in an AS trailer. You can most certainly pull more than 50A without doing anything very crazy. That's steady state and not counting any surge currents.

Bob

[Glen Carter]

That adapter should work, however as mentioned some of your system will be on a 20A circuit and some on the 30A circuit. You can plug into the 30A and see what works and what doesn't. Your main panel should have a dual 50A main breaker 3-4 circuits on either side. Labels should indicate what is powered. You will need to be more careful what you run on the 20A leg .... If the A/C and converter are on the 20A side, turn off breaker to converter ..... if running A/C, it will trip a 20A breaker.

[Glen Carter]

Originally Posted by uncle_bob

Hi

Nope

The 50A circuit is a 240V circuit. Each hot leg it 120V to the neutral. You get 50A at 120V off of each leg. Take a look at the AC panel in your trailer or the panel on the post at the campground. On either one you will see a dual 50A breaker controlling the circuit.

Indeed pulling 100A at 120V is unlikely in an AS trailer. You can most certainly pull more than 50A without doing anything very crazy. That's steady state and not counting any surge currents.

Bob

Agreed, the supply is most likely 50A/240V however the Airstream doesn't have any 240V split phase appliances. Agreed, the Airstream could pull more than 50A, but not on one leg.


If the site post has 30A on one phase and 20A on the other phase they could easily pull 50A or more with both A/C, water heater, converter and microwave. Plugging into the 30A+20A>50A will require close management of what's being used at one time. The Owners manual should show the power requirements for each circuit and what's connected.

[DaveG]

Will you be feeding the jury rig adaptor to an EMS before it gets to your trailer?
Ask yourself, do you feel lucky?

(In an ideal world: Circuit breakers are gate keepers. Wire (in most cases) is sized to the circuit breaker. So are receptacles. A 20 amp circuit is just that, and a 30 amp is just that. Wiring may vary in style and performance (distance from source, shared load on a circuit, etc. plus who did the work and condition of the components. Amps is the amount, volts the pressure, watts is resistance to the flow of electrons. We see it in our electric bill as a measurement of consumption. Smoke does the work. If you let the smoke out it will quit working. Old joke, sorry )

[Mollysdad]

Some confusion comes from calling it a 240 v. circuit. It COULD be 240 v. but the Airstream never uses 240v. Remember, the 50 amp plug has 4 pins, a ground, a neutral, leg 1 and leg 2. IF you were to take a meter and stick it across the pins leg 1 and leg 2, the meter would read 240 v.ac. But the trailer doesn't do that. Instead, meter from the neutral to leg 1 and it will read 120 v. The meter across the neutral and leg 2 will read also 120 v.ac. That's how we get two legs of 120v ac.

K.I.S.S.

[DaveG]

Originally Posted by Mollysdad

Some confusion comes from calling it a 240 v. circuit. It COULD be 240 v. but the Airstream never uses 240v. Remember, the 50 amp plug has 4 pins, a ground, a neutral, leg 1 and leg 2. IF you were to take a meter and stick it across the pins leg 1 and leg 2, the meter would read 240 v.ac. But the trailer doesn't do that. Instead, meter from the neutral to leg 1 and it will read 120 v. The meter across the neutral and leg 2 will read also 120 v.ac. That's how we get two legs of 120v ac.

K.I.S.S.

........
And a thought to consider - A shared neutral has a risk in that if it ever goes open the result may be 240 volts passing through 120 volt devices. Possibly another reason to avoid unconventional connections. In the case of the 20 + 30 connection it could be both ungrounded legs are off the same buss in the source load center...? "Hey it works so it must be okay" is not always a sign that it actually is okay.
........

[Thiss]

I think you will just have to live with one AC at this location.

[uncle_bob]

Hi

The 50A RV circuit very much needs to be fed with 240V. The lack of or presence of 240V loads does not matter. If you feed both hot wires in phase then all the current goes down the neutral. You get no cancellation. Since you have 50A breakers, this could be 100A of current down a 50A wire and connector.

The breakers will not trip since you are under 50A on each of them. In this respect the neutral is "unprotected". That's because it's intended to be used with 240V.

Since you are putting 4X the heat into the contacts and wires at 100A, it's a pretty good bet that you will have big problems. Even at a much lower current level, you are likely to get into trouble. Just what level depends on the temperature outside and what sort of shape this or that is in.

Normal duty for a 50A wire and connector would be 80% of 50A (so 40A). You are already getting it a bit warm at 50A. Not dangerously warm, but still heading that direction.

Bob

[GeeSag]

I was wondering how are typical RV campgrounds wired from the main breaker to the 30 + 20 amp pedestal.
Is it common for the 20 amp to be on a separate phase from the 30 amp?
This question applies to the OP situation of a pedestal without 50 amp receptacle.
Do campgrounds wire the pedestal off one phase, or separate phases for the 30 and 20? Probably anybody's guess. it would be easy enough to measure the voltage between the two hot sockets and see if it measures 120 or 240.

So I went looking for a typical pedestal.
This one from Home Depot:
https://www.homedepot.com/p/GE-RV-Pa...32SS/203393633
and I looked at the details.


Does anyone else see a problem.
Is the schematic wrong, or do I just have in my mind the hot and neutral side of a plug backwards.
Look carefully at figure 2.
Do they show running the hot lead to the neutral side of the receptacle?

[uncle_bob]

Hi

A 30A RV circuit is single phase / 120V. When you run a cable over to it, you would have a single phase feed. The typical setup is to put a 30A breaker ahead of it and let the camper decide if he wants 15A or 20A or 30A. The operative word there being the or rather than and. Since it's single phase, it goes hot to neutral. That's how all single phase AC wiring is done.

*Could* you wire it up with a 240 V feed and split it at the post? Sure, if you wanted to maximize the cost, that would be a great way to do it. Wire is a big part of the budget and you have one more chunk of copper in the 240V feed. It's just money. ( Any bets about the local RV park going with the higher cost option? ..... )

Is this "one at a time" sort of thing against the rules? Nope. You house is wired the same way. Pull max current on all the circuits in the house and the main breaker trips. Plug a 15A load into more than one outlet at a time an the breaker on that circuit trips. It's a very common way to do things.

Bob

[ITSNO60]

Originally Posted by GeeSag

So I went looking for a typical pedestal.
This one from Home Depot:
https://www.homedepot.com/p/GE-RV-Pa...32SS/203393633
and I looked at the details.



Does anyone else see a problem.
Is the schematic wrong, or do I just have in my mind the hot and neutral side of a plug backwards.
Look carefully at figure 2.
Do they show running the hot lead to the neutral side of the receptacle?

Yes you have a good eye, that diagram has the 20 amp receptacle wired backwards. Ironically an electrician wouldn't even bother to look at the diagram because it's such a basic hookup but an inexperienced DIY or park maintenance person might carefully follow the diagram and end up with reverse polarity which gives credence to the whole "qualified persons" thing.

Over the years I've seen incorrect instructions on appliances, more so now that nothing is made or printed here anymore. There were some big name clothes dryers coming with instructions to bond the ground and neutral on a 4 wire hookup and some speed ovens with instructions for the circuit in violation of code. Don't believe everything you read.

[richard5933]

Originally Posted by GeeSag

I was wondering how are typical RV campgrounds wired from the main breaker to the 30 + 20 amp pedestal.
Is it common for the 20 amp to be on a separate phase from the 30 amp?
This question applies to the OP situation of a pedestal without 50 amp receptacle.
Do campgrounds wire the pedestal off one phase, or separate phases for the 30 and 20? Probably anybody's guess. it would be easy enough to measure the voltage between the two hot sockets and see if it measures 120 or 240.

So I went looking for a typical pedestal.
This one from Home Depot:
https://www.homedepot.com/p/GE-RV-Pa...32SS/203393633
and I looked at the details.


Does anyone else see a problem.
Is the schematic wrong, or do I just have in my mind the hot and neutral side of a plug backwards.
Look carefully at figure 2.
Do they show running the hot lead to the neutral side of the receptacle?

My guess is that lots of older campgrounds and those done on lower budgets will have one circuit feeding both the 30 and 20 amp outlets. Some newer ones might have two circuits, but if they have two then they're likely to just install the 50-amp service and be able to charge more for the site.

Me? I'm going to assume that on a pedestal with just 30 & 20 amp outlets that they're both sharing the same 30-amp breaker and play it safe unless I'm told otherwise.

[jeffmc306]

Originally Posted by stevejones

Our trailer is a 50A trailer with two ACs. We're staying in a park where all I have is a 30A hook up. As I hooked up the dogbone to the cable and to the box I saw the 20A circuit that was also in there and wondered, can you use the 30A circuit and the 20A circuit together to make a 50A circuit or at least be able to run both ACs? Especially since we have Easystarts in both units. Maybe using something like this:

https://www.homedepot.com/p/Camco-50...B&gclsrc=aw.ds

Thoughts? Opinions?

Steve

Steve, if you have Easy Starts on both A/C units, you can run both on 30A service. At least that’s what they told us at the MicroAir booth in Fryeburg. No need to mess with the 20A circuit.