Could someone describe 50A shore power systems?

[DavidM]

I am making the transition from boats to RVs. Most electrical systems are the same but one I am a bit confused about is 50A shore power systems on RVs.

On boats, very few marinas have a single phase 120V/50A service. Almost all have 240V/120V/50A where the two legs are usually split inside the boat and serve two separate 120V busses. Sometimes there is also a 240V service like a big A/C that is served from a separate breaker.

On RVs I am not sure. I do know that 30A systems are the same as both RVs and boats use a single leg 120V supply but boats use a round twist lock connector and RVs use a crowsfoot spade connector but besides that difference they are the same.

Can someone explain the typical 50A service in RVs?

Thanks, David

[Goodspike]

I think your boat situation is basically the same, except that you probably have to get into a $500,000 plus RV to get a device that has 240 volts. Often the second circuit is dedicated to a second A/C unit., so only 20 amps of the second 50 amp side is being used.

As to 30 amp, my RV does use a round locking twist connector (which has a second proprietary twist lock too) on the power inlet, like what most 3000 watt generators non-RV generators would use. It makes it a bit harder to find cords because it has to be RV on one end and generator style on the other. But yes, other than that they are the same. The problem is they tend to be undersized such that running multiple devices is likely to trip the main breaker. An A/C by itself is on a 20 amp circuit. Add in a microwave, hair dryer, electric water heater and somethings got to give!

[Morich]

I might first point out that there are likely to be hundreds of small differences in various RV as there are many more options involved and that makes "general" or "common" descriptions okay but if you want to get down to how they actually operate, it requires a closer look. I'm not sure there is one Typical method that I could point to as there are multiple items that may/may not be involved like auto transfer switches which sense whether to use the power cord or switch to the generator power. Simple systems which the user changes the power cord from the generator outlet to the shore power outlet, is another way to do the transfer. Then some RV will have a "load shedder" which automatically cuts power to systems considered less vital when power gets short.
Would you be able to narrow the question a bit more or point to a less general question? Perhaps cutting it down to what is done on trailers versus motorhomes or a size or type to kind of home in a bit?
Once we get past the shore power plug, I'm hard pressed to spot a typical but most of us would have more experience with one over another but that might not make it "typical" for other users. Throw in solar power and "typical" gets pretty wide!
I might also throw in that confusion on electrical systems seems to be very typical!

[Goodspike]

Originally Posted by Morich

I might first point out that there are likely to be hundreds of small differences in various RV as there are many more options involved . . ..

I think the OP is asking more about the basics rather than specifics. But on the topic of options, other recent threads have pointed out that some RVs come with a 50 amp upgrade, or stated differently, very similar RVs can have either a 30 or 50 amp service. I would highly recommend opting for the 50 amp service is possible, unless maybe the main use of the RV is boondocking.

But other factors may not make that possible. Maybe getting a 50 amp service means an extra $10,000 of expense, or some other disadvantage. As an analogy, I would have loved to have had leather seats in my truck, but it wasn't worth the extra $6,000 of cost including all the other options required for leather, including many I not only didn't want, but wanted to avoid!

[DavidM]

OK, I think Goodspike answered my basic question- RVs with 50 amp service use 240V/120V/50A shore power connector and split the two legs inside and often dedicate one leg to the A/C. That is exactly like boats.

I realize that RVs have ATCs and power management systems which very few recreational boats have.

Also DC systems have lots of variations but in general those are the same as on boats: solar panels, inverters, chargers, inverter/chargers, etc.

Thanks, guys
David

[Goodspike]

These four diagrams would show some Winnebago systems. Two are 30 amp and two are 50 amp if I recall correctly.

http://www.winnebagoind.com/diagram/2000/131741.pdf

[sundog964]

In our RV, we have the 50 amp option with 2 AC units. Vista 29V. When you are on 30 Amp service, you can only use one of the AC units, but either one. It is controlled by an automated power distribution panel in the galley. Quite sophisticated.

[Morich]

That's what I was getting at.
The plug and wire to the RV are pretty standard except some differ in the way they connect but once it enters the RV, where it goes is going to depend on lots of options, even after we decide which year, make, model and length.
Which is typical? I guess it's the last one we looked at!

[creativepart]

David, I usually see RV 50amp shore power described as “two separate 120v 50amp legs.” Could they be wired 240v in the RV? Sure, but that’s uncommon.

It could be more common on boats because 240v is so common internationally.

There are million dollar bus-type coaches that might have a 240v dryer or boiler in their RV. But in RVs like the more common Winnebagos, Tiffins, Newmar’s, etc everything is wired into two separate 120v circuits and nothing is 240v.

[imnprsd]

All RV shore power poles I have seen have a 50A plug and/or a 30A plug and/or a 120V common house hold 20A plug.

A 50A power pole at the RV site will have two 50A wires known as L1 and L2. ...And there is no such thing as a 30A hot wire. This is just how we like to refer to it, because their is always a 30A plug available when a park does not offer 50A service.

We call it 30A because the wire gauge and the circuit breakers determine the naming convention, but this really is just a signal they have limited the load by installing a 30A main breaker... and inside the circuit panel you find additional safety circuit breakers that trip at 15A or 20A. Note: The 30A breaker you see is my inverter circuit breaker. And like all breakers, this one is designed to trip when the load on the circuit calls for more than 30A. Howere, as mentioned before, the L1 and/or L2 power lines are 50A capable.

Note: Circuit breaker only monitor the L1 or hot lead. They do not monitor the return line or neutral wire we refer to as the "white wire."

Consequently, RVs that only offer 30A service do have a different plug, but when you connect to the 30A shore power socket you are really getting the L1 branch at 50A. This wire is usually red but it also can be black.

And since current is "on demand" a 50A and a 30A RV needs to have a Energy Management System (EMS) that will shed (drop) appliances to limit over current when hooked up to 30A service. And in most RVs they use an EMS made by Intellitec. In my RV this is the "Powerline" display panel, but my EMS control board (EMS620) is mounted inside my Sub-Panel. (See picture.)

Note: My 50A RV includes a transfer switch that gives priority to the Generator over shore power. And my Generator produces 240V just like the shore power pole. However, the transfer switch is wired for 120V use.

Note: In my Dimensions Inverter/Charger there is also a transfer switch that senses when to turn the inverter function on-and-off. I.e., one of the 50A hot wires (Either L1 or L2) is fed to the inverter/charger and will pass thru to the Sub-Panel (aka 30A Sub-Panel). Consequently, when there is shore power the inverter function will automatically turn off and the charger function can and re-charge the house batteries.

And when an RV park only has "30A Service" I can use a 50A to 30A adapter. However, the key point here is that the 30A adapter really just bridges both 50A legs to L1. (See picture below.)

This way both of the "Hot" Bus Bars in the the circuit breaker box are live; and the EMS will sense there is only one hot lead (L1) and then the EMS will monitor and shed appliance loads as necessary to protect the system; and it takes some user help here to not overload the system when on 30A power.

For example: When using 30A service you do not want to operate a hair dryer or floor heater in combination with your microwave at the same time, because you will be pulling over 3000W which is 25A. Consequently, circuit breaker is there to protect (and trip) when the current on any one line exceeds 15A or 20A.

This why wall sockets are designed differently and look different for 15A vs. 20A use. And as mentioned before, different amp service uses different wire gauge to cut cost. ...Everything has a standard (code) and visual clues if you know what to look for.

Here's the 50A power grid I diagrammed for my coach. I also included the EMS control board located in my Sub-panel you'all might like to call my 30A panel. This is typical power grid for Winnebago Class A motor homes. However, your RV system maybe different.

[DavidM]

Thanks guys, you have fully answered my question. I think creativepart's last post hit the nail on the head. Boats are the same. You have to get up to a million $ and above to find a 240V appliance on a boat.

Where RVs depart are power management systems (heard about them but never saw one on a boat) and automatic transfer switches (also very uncommon on boats). Maybe boaters want more personal control .

FWIW I was talking with my good friend who has a 2005 WBO Class A gasser. He was telling me about a device that turns off some appliances when the power requirements get too high. I said no way, that kind of system is only used on $million boats, surely they didn't put one on your RV. Well sure enough his has one.

David

[imnprsd]

The big boats use 3-phase, 208V motors too. RVs don't.

[Morich]

Originally Posted by DavidM

Thanks guys, you have fully answered my question. I think creativepart's last post hit the nail on the head. Boats are the same. You have to get up to a million $ and above to find a 240V appliance on a boat.

Where RVs depart are power management systems (heard about them but never saw one on a boat) and automatic transfer switches (also very uncommon on boats). Maybe boaters want more personal control .

FWIW I was talking with my good friend who has a 2005 WBO Class A gasser. He was telling me about a device that turns off some appliances when the power requirements get too high. I said no way, that kind of system is only used on $million boats, surely they didn't put one on your RV. Well sure enough his has one.

David

That would be the "load shedder" and they are more common in the larger or more "fully optioned" RV and part of the reason I like to go to actual plans for the wiring as there really are just too many to begin to guess as things do change even more than once a year.
If interested in getting more indepth, this is a great site for actual plans for the electronic part and you can already tell that you are wading into a very deep subject with lots of confusion.

Wiring Diagrams

[Goodspike]

Originally Posted by creativepart

It could be more common on boats because 240v is so common internationally.

I'm not sure their 240 is the same as our 240, I've never researched that. Somehow I don't think it is or else they would likely have 120 too!

[DavidM]

Even a very big boat can make it with 240V/120V/50A shore power. That is enough to power three 120V, 16,000 btu A/Cs (typical max for 120V), and at least a microwave and a water heater (electric only on boats) simultaneously. Probably up to 60' which is the biggest that can usually be handled by the owner.

Beyond that you do get into three phase power supply for the big ones, probably 480/3 phase.

Yes international power is different. It doesn't have a neutral and all home AC loads are handled with 240V. Something different about grounding but forget what.

David

[creativepart]

My Gas class a has very effective power management with a Precision Circuits Inc, Power Control System.

It manages amps by shedding appliances and even is connected to to inverter to take extra amps via the inverter to augment available power when on 30-amp. It was standard equipment.

[Goodspike]

Originally Posted by DavidM

Yes international power is different. It doesn't have a neutral and all home AC loads are handled with 240V. Something different about grounding but forget what.

David

Well, I did some research, but not too much, because as Ferris Buehler would say:

I'm not European, nor do I plan on being European, so who gives a crap if they're [240 volts]? It still wouldn't change the fact that I don't own a [60 foot yacht]!

Anyway, it appears it's 240/480, although I don't think they use the 480 for anything residential. Apparently the 240 allows them to run line further from transformers.

https://electrical-engineering-porta...bution-systems

[lenny-shawna]

Originally Posted by creativepart

David, I usually see RV 50amp shore power described as “two separate 120v 50amp legs.” Could they be wired 240v in the RV? Sure, but that’s uncommon.

It could be more common on boats because 240v is so common internationally.

There are million dollar bus-type coaches that might have a 240v dryer or boiler in their RV. But in RVs like the more common Winnebagos, Tiffins, Newmar’s, etc everything is wired into two separate 120v circuits and nothing is 240v.

Newmar Essex and King Air have 240v dryers and I also believe 240v induction cook tops. Typically, each 120v leg will supply a portion or the rv. On mine, my cord reel failed on one 120v leg so basically half the rv had no power but the other half did. Once I replaced the reel (cord was fine) everything worked great.

[mrschwarz]

US residential systems are 240 volts, with a center-tap neutral. Voltage between the center-tap and either leg measures 120V each leg is out of phase with the other. Every 50-amp RV I have seen is wired similarly to residential electrical systems. Each 120 volt hot leg is wired to one side of a 240 volt load center. Breakers in the panel alternate between one leg and the other so any two adjacent full-size breakers go to different legs. 120-volt loads, such as electrical outlets and air conditioners are wired to one side or the other in the load center. Designers try to balance the loads equally between the two sides. If a 240 device is wired in, it is usually connected to two adjacent positions. Many RVs use 1/2 position breakers so they can fit more in a smaller load center. In the case where this is done, adjacent breakers can be on the same 120-volt leg.

Some Tiffins (and I imagine others) use 240-volt cook tops and other appliances. When a 30-amp dogbone is used, both legs in load center are on the same 120-volt leg. When this happens, 240 volt appliances don't see any voltage at all and won't work.

I can't imagine boats are any different, other than the absence of some of the automatic energy management systems some RVs have. 240 volt systems in Europe are incompatible with an RV or marine system like this. They are wired the same way, but the voltage is doubled. Instead of 120 volts between the neutral and hot leg, the voltage is 240 volts. Any outlet or device wired for 120 volts would see 240 volts.

I would image any boat would be natively wired for either 120 volts or 240 volts. If it was traveling, it would have either a step-up or step-down to convert from one to the other.

[dkoldman]

FYI, for extra knowledge.

The 50-amp 120/240-volt 3 pole 4