breaker location for 3rd airconditioner

[mtlakejim]

We are off subject from original post but I think it is important information that we need to understand and as such the conversation should not be deleted or moved.


Fairly obvious that the RV industry and owners are moving toward every increasing power consumption. We all need to understand what the limitations of camp power means as it relates to same. Adding a third AC certainly relates to that and as such this conversation is relevant. I would think a thread should be allowed to continue as long as the conversation moves along similar to what it would around a campfire.

[BB_TX]

Originally Posted by mtlakejim

That would suggest that they are wiring to cover all three breakers at full load at each site IE: 50 + 30 + 20amp = 100.
........

A 120/240 vac 50 amp split phase system protected by a 50 amp breaker allows up to 50 amps on each hot leg, which means up to 100 amps total from that one connection since each hot leg is independent of the other as far as max load carrying limit of each leg is concerned. By connecting a 20 amp circuit breaker to the line side of one leg of the 50 amp breaker, that hot leg (H1) from the main panel could potentially carry the sum of the two for a total of 70 amps. And if a 30 amp circuit breaker was connected to the line side of the other hot leg of the 50 amp breaker, that hot leg (H2) from the main panel could carry the sum of those or up to 80 amps total. So if all breakers were operating at their max current that could be up to 150 amps total (50 x 2 + 20 + 30) to that one pedestal, split between the two hot wires coming from the main panel.

[mtlakejim]

[QUOTE=BB_TX;1149349]A 120/240 vac 50 amp split phase system protected by a 50 amp breaker allows up to 50 amps on each hot leg, which means up to 100 amps total from that one connection since each hot leg is independent of the other as far as max load carrying limit of each leg is concerned. By connecting a 20 amp circuit breaker to the line side of one leg of the 50 amp breaker, that hot leg (H1) from the main panel could potentially carry the sum of the two for a total of 70 amps. And if a 30 amp circuit breaker was connected to the line side of the other hot leg of the 50 amp breaker, that hot leg (H2) from the main panel could carry the sum of those or up to 80 amps total. So if all breakers were operating at their max current that could be up to 150 amps total (50 x 2 + 20 + 30) to that one pedestal, split between the two hot wires coming from the main panel.[/QUOTE

If that is correct then you would expect code would require that the supply wire to the pedestal would have to be rated for at least the 150amps?? But perhaps the code writers are making an assumption that no one would ever use both the 30 and 50 amp at the same time? Those assumptions would have been based on much smaller and lower power use trailers several years back and therefore the reason for the more recent increase in requirements?

Like I said we need a certified electrician to verify.

And it is quite reasonable to expect some campgrounds will have much more robust system than others is it not? So I guess it goes back to "it depends"?

Ultimately it goes back to can we run three AC units when we need to (trust me in the triple digit desert heat you NEED three on a 42' 5er). I know you can at our campground and would suspect that most of the modern campgrounds could accommodate it. After all it is not unusual at all in the south to have the two factory roof AC units going to cool inside and be using the 20 amp plug for as many fans as it can turn outside to cool off the picnic gathering. So I would say in most cases you can run three AC units if, like we do, you have one on the 20 amp 110 direct or even on a separate leg of the 50amp as long as you don't run a lot of other appliances while doing so. Since staying cool is usually the priority if we needed to we would adjust. But keep in mind that running the third AC power completely independent for the reasons I have stated earlier is a significant advantage. Which is what I was trying to convey to the OP at the start of the thread. Granted there may be some old parks where the aging power system may not handle the extra load. But I for one try to avoid those types of parks anyway as they usually are not very well suited for a modern large 5er.

[BB_TX]

Originally Posted by mtlakejim

If that is correct then you would expect code would require that the supply wire to the pedestal would have to be rated for at least the 150amps??
......

In the scenario I noted, one hot wire from the main panel could carry a max of 80 amps, 50 + 30. The other hot leg could carry a max of 70 amps, 50 + 20.

However due to the unique nature of a 120/240 vac single phase/split phase system, even though both hot legs can potentially simultaneously carry 50 amps, the neutral wire will never carry more than 50 amps. And if both hot legs happen to each be carrying the EXACT same amount of current, the center tap neutral wire would be carrying ZERO amps. It takes a schematic diagram to fully understand that one. But since hot 1 and hot 2 are 180 out of phase, the current in each is always traveling in opposite directions. And since they use a common neutral, the neutral currents are trying to flow in opposite directions in the same wire at the same time, which of course is not possible. So they are off setting.

However, again with the scenario above, if one hot leg of the 50 amp service were carrying 50 amps, the other leg of the 50 amp service were carrying zero amps, the 20 amp service were carrying 0 amps, and the 30 amp service were carrying 30 amps, the neutral wire would be carrying up to 80 amps IF the 30 amp breaker were on the same hot leg as the 50 amp service hot leg carrying the 50 amp current. So, assuming the 20 amp breaker and the 30 amp breaker were on different hot legs, no individual wire would carry more than 80 amps.
Whew!

Someone here posted recently they were an electrician. Hopefully they will pop in and further clarify.

[mtlakejim]

Bill,
For the sake of discussion I will assume that you are correct until we hear from an electrician.


But can we safely say that you CAN run three A/C units on one pedestal if you have 50amp and plug the third into the 20amp?


Can we also safely run two A/C units if your plugged into 30 amps and run the second A/C off of the 20amp?


If the answer to both of the above is YES then we have answered the OPs question.


For certain I can say it works for three on 50amp service as we are doing it with no problems at all, at least where we are at.

[BB_TX]

Based on the 30 amp breaker and the 20 amp breaker being independent of the 50 amp breaker the answer to both is yes. You can run the extra A/C by running it from the pedestal 20 or 30 amp breaker.

[mtlakejim]

Originally Posted by BB_TX

Based on the 30 amp breaker and the 20 amp breaker being independent of the 50 amp breaker the answer to both is yes. You can run the extra A/C by running it from the pedestal 20 or 30 amp breaker.

I didn't quite phrase the second question correctly.

Can we run two AC units at a 30amp site (IE: no 50amp) if one is plugged into the 20amp 110?

[BB_TX]

And I didn’t answer particularly clearly.

If the RV is plugged into the park 50 amp service and running 2 A/Cs, you can run a 3rd A/C from the pedastal 20 amp outlet. You could also run that extra A/C from the 30 amp outlet, but it would probably not really be providing the correct over current protection. The A/Cs installed in the RV are protected by 20 amp breakers.

If the RV is plugged into the park 30 amp service and running one A/C, you can run a 2nd A/C from the pedestal 20 amp outlet.

[StageCoachDriver]

Originally Posted by BB_TX

Does that mean that even though you have three A/Cs you can only actually run two at a time?

The standard electrical configuration is 50 amps. Three A/C units will draw close to or over the 50 amps, so if you use the microwave, you'll be over and perhaps pop the circuit breaker on the power pole.

[BB_TX]

Originally Posted by StageCoachDriver

The standard electrical configuration is 50 amps. Three A/C units will draw close to or over the 50 amps, so if you use the microwave, you'll be over and perhaps pop the circuit breaker on the power pole.

You are correct it is 50 amps. But the 50 amp service actually has two separate hot legs with a max current draw of 50 amps EACH, typically referred to as H1 and H2. That gives the potential of 100 amps of 120 vac service, or 12,000 watts of power. Two A/Cs pulling about 30 amps (15 amps each) on one hot leg H1 would leave 20 amps still available on that hot leg. And the 3rd A/C on the other hot leg H2 pulling 15 amps would leave 35 amps still available on that hot leg. By carefully balancing the other high current loads among the power available you could run all three simultaneously on the 50 amp service. But there would still be the risk of tripping the main breaker if too much were operating at the same time. That is probably why they install the transfer switch.

[DQDick]

On my installation the third AC is wired to a 20 amp breaker mounted in the basement then the wiring goes to a 30 amp RV plug in on the side of the rig. I use a 30 amp rv cord to go to the pedestal and then a 30 amp ems before the pedestal. I also have dog bones so the whole thing can be plugged in to a 20 amp outlet if need be.

[BB_TX]

And that would be the wise thing to do to maximize the availability of all 3 A/Cs.

[mtlakejim]

As always we can count on DQDick to step up and tells us how to do it right!




Point is though that you can run three AC units with no problem on a site that has 50amp service and two at a site that has 30amp service IF you run the extra A/C completely separate of the original two roof units. So there is a reaaaaalllllllyyyyyy good reason to go to the extra trouble of running the power to your add on third A/C separately (and it really isn't that much trouble to do it).


Back when we were weekend warriors and visited a LOT of RV parks with only 30amp service (or at least the ones we could get at the time were), many were the times I wish we had a second A/C running!!