breaker location for 3rd airconditioner

[dbcustom]

My Montana is pre-wired for a 3rd AC, just installed the unit but the circuit doesn't have power so before I put my tracer on it thought I would check here first.

Since all of the breakers are being used I figured they might he it tied in the one of the other circuits?

Thanks in advance.

[jeffba]

It shares power with one of the other AC units. I think they just use a transfer switch to switch between 2 of them.

[dbcustom]

Thanks I figured it would be shared with another feeder when I didn't see a 3rd AC breaker. I just installed the unit so I figured I would check here while I took a break.

Thanks for the help

[BB_TX]

Originally Posted by jeffba

It shares power with one of the other AC units. I think they just use a transfer switch to switch between 2 of them.

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

[DQDick]

Yes usually it shares power with the bedroom AC in front bedroom models anyway. On our rig we have a wooden vent next to the door and when I took that out that's where the transfer switch was. Now there's a breaker in the basement for my third AC and it runs off the 30amp plug in the pedestal. I installed a 30amp plug to feed it on the side of the rig and now all three run at the same time..

[jeffba]

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?

Yes, unless you do what Dick did.

[DQDick]

One other thing to remember. If you add the third AC and feed it into the ducts you will need to add more vents if you run all three at once. The vents we have are the minimum Dometic says a two AC unit should have. That's why I've opened most of my vents by half and the third AC isn't ducted.

[BB_TX]

Originally Posted by jeffba

Yes, unless you do what Dick did.

Interesting. What controls the transfer switch? Does it automatically cycle between the two A/Cs based on some defined control parameter? Or is it user controlled to select one or the other?


And what is the benefit other than cool air distribution since it doesn't add cool air volume unless you do as Dick did? This coming from someone who had to add even a 2nd A/C to their rig.

[DQDick]

As originally set up, the bedroom AC has preference. When it shuts off the 3rd AC then comes on. Since the bedroom or other smaller room had control, it won't need to run all the time so you will get additional cooling, just not enough for us. Today we are expection actual temps over 100 (currently 99) and heat index over 110 and we're in full sun.. Most folks are smart enough to move when it's like this so the original setup for the three will work for those folks.

[mtlakejim]

We live full time in the New Mexico Desert in direct sunlight as in no shade!! One of the best test locations for A/C performance! DQDick is our neighbor during the winter. We currently use a large portable A/C we bought at Wal Mart for about $400. It runs off an extension cord that is plugged into the 20 amp 110volt plug in on the campground pedestal. Basically completely independent of the rest of the 5th wheel electrical system. This has two major advantages:
You can run 2 ACs at a 30amp site and 3 at a 50amp site.
If for any reason the coach loses power you still have at least one A/C to save the puppies!
We monitor our setup with a TempStick brand device that texts us if the interior temp gets to high so we can save the puppies if needed. But so far we have been very pleased. With the two roofs set on high fan and 72F and the portable on high fan at 76F we have never gone above 78F even on an extended 6 days in a row over 100F ambient temp. On days in the mid nineties we run at 74F all day long (the tempstick graphs the temp on their app as well). It should be noted that we turn off the 3rd AC at night and set the two roof AC units to auto fan as the temp usually drops off substantially in the desert at night. The 3rd AC is primarily as a safeguard to protect the pups and adds just enough to take the edge off of midday heating.
We plan to add a third roof AC later for aesthetic and possibly performance reasons. BUT I will go to the extra trouble to run a SEPERATE electrical line from that A/C to the exterior wall so I can use a separate extension cord to plug it in just like the portable unit. We could and may even have the coach setup with FOUR A/C units if we do like Dick and use the 30amp plug for one of them!!! In that case we would set one of them really high to serve only as an emergency backup. The things we will do for puppies......


Couple other things we have done on advice of others was to use PVC pipe to open up our living room AC intake ducts and cut every other vane off of the discharge vent covers on the discharge duct. Our larger West facing windows have foil backed reflective covers on them (you can't see it from the outside during the day) and we usually have most if not all of the window shades on the sunny side drawn down.


Still we hope to retire in a few years and get the heck out of the no tree/blazing sun of the NM desert!!!!

[BB_TX]

A somewhat related question considering how Dick and Jim use a 3rd A/C. On a park power pedestal, are the 30 amp breaker and 20 amp breaker wired as sub breakers from the 50 amp breaker? Or are they wired in parallel to the 50 allowing the potential of full current from all simultaneously? Or is the answer “it depends”?

[mtlakejim]

Originally Posted by BB_TX

A somewhat related question considering how Dick and Jim use a 3rd A/C. On a park power pedestal, are the 30 amp breaker and 20 amp breaker wired as sub breakers from the 50 amp breaker? Or are they wired in parallel to the 50 allowing the potential of full current from all simultaneously? Or is the answer “it depends”?

It is my understanding that they are wired parallel at least at our park. I am fairly sure that most other parks at least have enough wire to carry a full 50amp load plus the 20amp. You would think so at least since they should expect that folks would run their campers and also plug in stuff on an extension cord on occasion and they have to wire for anticipated MAXIMUM load. Now are they wired to run both a 30amp and 50amp simultaneously? That would be a different question.

I will say this, we bought a surge protector that shows the Amp draw on each leg of our 50 amp service. I found out that both of our factory installed roof airs are on the first leg and they run about 28amps when both are running with fans set to high. So in theory I suppose if you could get them past the initial start surge with a soft start setup they could both run on a 30amp plug but you would not be able to run anything else on that breaker/plug. But as most here know what is possible in theory doesn't always work out in the real world.

As you say, "it depends". And I suspect it depends on what the code is for a given area. Any certified electricians out there to give us a good answer? My understanding is it would have to be wired to carry the max load of all breakers. Just like your house.

It is my understanding and I could be wrong that the 50amp service is two 50amps while a 30amp is only one. Again can a certified electrician step up and confirm?

[BB_TX]

50 amp service is definitely 50 amps on each hot leg for a potential of 100 amps total current draw if both legs were pulling max current. And 30 amps is only 30 amps since it only has one hot leg.

I guess I would be a little surprised if a park went to the expense of wiring the pedestals to fully support both the 50 and 30 simultaneously since they would expect an RV to only plug into only one or the other. I could see the 20 being wired independently.

[mtlakejim]

Ok I found this on the web. Looks like code only requires a MINIMUM of enough wire to handle the full load of the 50amp service at one time. Basically what I take from that is you can potentially overload the pedestal as a whole IF you ran the 50amp AND the 20 or 30amp service also at full load.


But lets be realistic. Three AC units all at once is only 45amps max. And you know any electrician worth his salt is going to wire for at least a little extra. So you can run 3 AC units all at once on 50amps but not much else just to be safe.


I think where you might get into possible trouble is at old campgrounds with subpar electrical systems. Campground designers before the 1990s probably never expected the kind of massive electrical hogs we have today. Particularly those private owned, barely making ends meet type places that haven't upgraded their power system in decades.

The Electrical Service supplying an entire RV park must be sized to accommodate the electrical demands of multiple modern recreational vehicles drawing power simultaneously from the individual park sites. The sum of the individual sites within the park, with some additional math applied, determines the total service size for the park.
Per the 2017 NEC, when calculating an RV park service, the load that you count for a single RV site equipped with a 125/250 volt, 50-ampere receptacle has been increased from 9600 volt-amperes to 12,000 volt-amperes.
The load you count for a single RV site equipped with both 30-ampere and 20-ampere receptacles remains unchanged at 3600 volt-amperes. The load counted for a 20-ampere RV site receptacle is 2400 volt-amperes. And the load counted for each 20-amp supply provided at each dedicated tent site is 600 volt-amperes.
The individual RV sites within an RV park are equipped with “supply-equipment” so that the RVs can connect to the available electric. These individual supply enclosures typically consist of more than one receptacle. When a multi-receptacle supply enclosure is dedicated to just a single RV, the load that you count toward determining the size of the entire park service is based on the single highest rated receptacle within that multi-receptacle enclosure. For example, if it contains a 50-ampere as well as a 20-ampere receptacle, you would only count the 50-ampere. However, where the supply enclosure is expected to serve two recreational vehicles, the load you count toward sizing the park service is calculated using the two highest rated receptacles within that enclosure and not just the one.

[BB_TX]

From the post above;
“When a multi-receptacle supply enclosure is dedicated to just a single RV, the load that you count toward determining the size of the entire park service is based on the single highest rated receptacle within that multi-receptacle enclosure. ”

That seems to indirectly state that lower amp breakers are subs from the highest amp breaker limiting that pedestal to the amp rating of the highest amp breaker in that panel. That would certainly make sense.

Normally you would not expect 3 A/Cs to be wired from the same hot leg of a 50 amp service. But if two were wired to the same leg inside the trailer, and you externally connected the 3rd to either the 30 amp or the 20 amp pedestal outlet, and not knowing which hot leg the 30 and 20 were subbed from, you could well end up with all 3 on the same hot leg. And at approx 45 amps for 3 A/Cs, if some other high amp device such as the microwave, water heater, etc were on that same leg it could easily trip the pedestal 50 amp breaker. If either leg of the 50 amp breaker exceeded 50 amps it would trip both legs even if the other leg had no current draw at the time.

[mtlakejim]

Originally Posted by BB_TX

From the post above;
“When a multi-receptacle supply enclosure is dedicated to just a single RV, the load that you count toward determining the size of the entire park service is based on the single highest rated receptacle within that multi-receptacle enclosure. ”

That seems to indirectly state that lower amp breakers are subs from the highest amp breaker limiting that pedestal to the amp rating of the highest amp breaker in that panel. That would certainly make sense.

Normally you would not expect 3 A/Cs to be wired from the same hot leg of a 50 amp service. But if two were wired to the same leg inside the trailer, and you externally connected the 3rd to either the 30 amp or the 20 amp pedestal outlet, and not knowing which hot leg the 30 and 20 were subbed from, you could well end up with all 3 on the same hot leg. And at approx 45 amps for 3 A/Cs, if some other high amp device such as the microwave, water heater, etc were on that same leg it could easily trip the pedestal 50 amp breaker. If either leg of the 50 amp breaker exceeded 50 amps it would trip both legs even if the other leg had no current draw at the time.

I disagree. All it says is that the rating for each pole is based off the highest amp breaker as it relates to the power requirements for the entire park. I am fairly sure that the 30 and 20 are not downstream of the 50 amp as you can still run either with the 50amp breaker thrown. I think the only code is that the wire that feeds the box has to be able to carry at least a full 50amp load plus safety factor (which they have upgraded in the new code).


Hopefully we have a registered electrician on here that can clear it up for us.

[BB_TX]

We have really gotten this thread off topic.

BUT. If the breakers are wired independent of each other (and I don’t dispute that) then the supply wire could potentially carry up to 80 amps. I can’t imagine any code that would permit wiring the supply for 50 amps in such a case.

[psomers]

My 2 cents. We camp often in a very nice COE park. Several years ago the park was being updated to 50A. They were doing one section at a time. All new main panels, pedestals and wiring. As I remember the pedestal cable was 4 wire. Two hot legs a neutral and a ground. One hot to 50A receptacle and 20A. Other hot to 50A and 20A. At main panel I believe 4 sites to one 400A breaker. Wish I had taken picture as my memory is not what it once was. If i am right 4 sites on same breaker better not be pulling more than 100A.

[BB_TX]

I was initially thinking about it from a cost standpoint. But it makes more sense from a functional standpoint to wire the 20/30 amp single pole breakers independent of the 50 amp double pole breaker. And I can see using 50 amp as the site rating for determining total park power requirements as you would not expect more than that from each site. But the breakers being wired independent means that it would be possible to pull a total of up to 70 amps from a hot wire connecting one hot leg to a 50 amp breaker and also a 20 amp breaker. And up to 80 amps from a hot leg connecting a 50 amp breaker and a 30 amp breaker. And if it is possible to do, then somebody, somewhere, at some time will find a way to do that. And not really that hard if a large 50 amp RV were pulling near max load and that person also had some high current device(s) plugged into the 20 or 30 amp pedestal outlet. And that would mean the wires from the main panel to the pedestal would need to be sized to carry up to 80 amps.

I think I have pushed this beyond where I should have stopped.

[mtlakejim]

Originally Posted by psomers

My 2 cents. We camp often in a very nice COE park. Several years ago the park was being updated to 50A. They were doing one section at a time. All new main panels, pedestals and wiring. As I remember the pedestal cable was 4 wire. Two hot legs a neutral and a ground. One hot to 50A receptacle and 20A. Other hot to 50A and 20A. At main panel I believe 4 sites to one 400A breaker. Wish I had taken picture as my memory is not what it once was. If i am right 4 sites on same breaker better not be pulling more than 100A.

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

Again I think it is a question to be answered by an expert.

For some reason a previous post didn't make it?