50 amp power management

[PAylor]

Hi all,

We have a 40 foot Augusta Ambition fifth wheel.  We have a progressive industries power management system which has a read out of power in and out.  The power is divided between two lines.  Of course we keep the power output under 50 amps.  Should we also try to keep each line under 25 amps?  On occasion one line has gone over 25 amps with no breakers blowing but I wasn't sure it was good to do.

Thanks in advance!

[jcussen]

If you are talking about a 50 amp campground breaker, you actually have 50 amps per leg, or 100 total. You will have to read your manual  to see if your management system can do 50 amps per leg. I know my surge guard system will handle it. With everything on, have seen 42 amps per leg [line].

[oldjohnt]

PA, good question. I agree with jc. Typical RV pedestal "50 amp" power can supply up to 50 amps on "EACH" leg, L1 & L2, which is why a 25 amp current draw wouldn't trip a 50 amp circuit breaker. Its NOT that you have ONLY 25 amps capacity on each leg.

NOTE I'm talking about the pedestal distribution NOT anything about your power management system.

Your RV power distribution is divided up among two legs of 50 amp capacity 120 VAC which in theory is good if kept balanced so no one leg is providing ALL your needs, but just because certain loads just happen to be operating that just happen to be served by one leg isn't necessarily cause for alarm PROVIDED THAT ALL ELSE AND THE DISTRIBUTION SYSTEM IS DESIGNED AND OPERATING CORRECTLY.    

I make no comment on the capacity of your power management system and if it can handle 50  amps per leg etc., but its good and safe to be aware of and concerned with power use and how its divided (hopefully somewhat balanced to some degree) in your rig.

PS is this what you have ???  http://tweetys.com/electrical-management-system-hardwire-50.aspx

John T   Longggggggggggg retired and rusty electrical engineer so NO warranty

[jcussen]

This may help you understand:

 http://www.myrv.us/electric/Pg/50amp_Service.htm

[Kirk W]

 

18 hours ago, PAylor said:

Of course we keep the power output under 50 amps.  Should we also try to keep each line under 25 amps?  On occasion one line has gone over 25 amps with no breakers blowing but I wasn't sure it was good to do.

If you examine the circuit breakers either for main power in the RV or at the power pedestal, you will find that it is actually 2 separate circuit breakers of 50a each and one passing one leg of the power supply. The two breakers are mechanically linked so that should either one experience more than 50a it will cause both to open. 

This means that in theory, you could use up to 100a of 120v electric power but since to do so each leg would have to see exactly 50a, the real world is that you probably have about 80a of total useful power available. It is very rare for any 50a rated RV to have problems tripping circuit breakers for the main power. But there is no need to set a 25a per leg limit as the limit is for each of the two legs. That does mean that when compared to the typical 30a RV you have far more than twice the power available but in fact, it gets very close to 3 times as much available power.

There is a lot of electrical theory involved in this but there is really no need for long discussions for the average RV owner. In practical application, the 50a RV cord actually has two power leads in it, each of them rated to supply a maximum of 50a and each one with a circuit breaker that will shut off all power. 

[oldjohnt]

Good info and picture Kirk. Indeed the two breakers, one for L1 other for L2, are for safety and/or other possible reasons mechanically tied together so if one opens the other does also. In many years of practice I've even seen where an "electrician" ? used a piece of wire through the handles (if not otherwise tied) to join two breakers.  While a professional electrician tech or engineer is well aware of what you so well described, if they were NOT tied a lay person or many typical RV owners might encounter a hazardous situation otherwise YIKES...........   

Best wishes Kirk and all here, be safe now

John T

 

[Barbaraok]

Paylor,

 You have an electrical management system.  Let it do its work.  The only time you should have to pay any attention to the loads is when you only have 30 amp available (older parks, etc.).   Then you will quickly learn how to balance and work with that limitation (only one significant draw on at a time).  But on '50 amp' power at the pedestal (which is really 100 amps as you see) unless you are paying for electric for the site, just go about your daily activities.

Barb

 

[richfaa]

what we did do when we ordered this 5th wheel was to make sure the  load on the legs were evenly distributed that is one A/C on each leg not both on the same leg etc. We  are nearly always on 50 amps and have never had a load issue on either leg. We do pay for our electric here on our Florida site and we use what we use. 

[oldjohnt]

3 hours ago, richfaa said:

one A/C on each leg not both on the same leg etc

That's a for sure Rich. The AC is one of the heavier current loads in an RV and its always best to balance loads (like L1 & L2 in a 50 amp RV) and to reduce current flow (wasted I Squared R losses) in the grounded conductor when possible.

I'm on the way to Florida to join you right now, it turned cold in North Texas and South Louisiana where I'm at a Walmart tonight brrrrrrrrrrrrrrrrrrrr

John T 

[Jack Mayer]

Well,  I cannot remember seeing a 50 amp RV wired with the AC on the same leg of service (when having only 2 AC units). And I've worked on RV electrical in countless rigs. Now everyone can tell me all the ones they have seen wired that way.....  Seriously, I'd like to know if people see that often...because I sure have not. Vern???

 

[richfaa]

15 minutes ago, Jack Mayer said:

Well,  I cannot remember seeing a 50 amp RV wired with the AC on the same leg of service (when having only 2 AC units). And I've worked on RV electrical in countless rigs. Now everyone can tell me all the ones they have seen wired that way.....  Seriously, I'd like to know if people see that often...because I sure have not. Vern???

From the factory not likely but one should confirm that. After market it happens.There are other high draw appliances that need to be checked.Hot water tank, MW, Etc and I said evenly distributed and used the A/C as a example should have known better on this forum.

 

what we did do when we ordered this 5th wheel was to make sure the  load on the legs were evenly distributed that is one A/C on each leg not both on the same leg etc. We  are nearly always on 50 amps and have never had a load issue on either leg.

[Kirk W]

1 hour ago, Jack Mayer said:

Seriously, I'd like to know if people see that often...because I sure have not. Vern???

I can't remember having ever seen one connected that way. It would be noteworthy poor design to do that.  

[oldjohnt]

2 hours ago, Jack Mayer said:

Well,  I cannot remember seeing a 50 amp RV wired with the AC on the same leg of service (when having only 2 AC units). And I've worked on RV electrical in countless rigs. Now everyone can tell me all the ones they have seen wired that way.....  

SAME HERE JACK, as a 47 year RV user and past RV dealer if a 50 amp RV has two AC units they were on two different legs, despite that I learned to NEVER SAY NEVER lol

John T

[Kirk W]

6 hours ago, oldjohnt said:

as a 47 year RV user and past RV dealer

Good grief! You must be even older than I thought! 

[oldjohnt]

5 hours ago, Kirk Wood said:

Good grief! You must be even older than I thought! 

Hey Kirk, you rascal you, I resemble that remark LOL The "first wife"  (I still call her that)  and I bought our very first "RV" in 1970, it was home made, bought on the south side of Indianapolis, and it fit on the back of our old Ford 4 x 4 pickup which we drove to Florida and hauled my Uncles boat back home, we came a long way since but a person never forgets their first unit and how I fixed it up and the fun we had.... The dog we took along with us died but the wife and I survived............

Best wishes

John T

[Dale P]

We never worry about it, unless we are on 30 amp service. Then we manage it, so we can run both A/C compressors

[jcussen]

2 hours ago, Dale P said:

We never worry about it, unless we are on 30 amp service. Then we manage it, so we can run both A/C compressors

How do you do that? Even with fridge on propane, and charger off, running two ac's normally trips my 30 amp circuit.

Thanks, Jim

[dewilso]

30A SHOULD RUN, 2 A/C units. Note the 2 underlined words.

[Barbaraok]

Two A/C units will run on 30 amps as long as they don't 'come on' at the same time - that's the kicker.  

[jcussen]

Using an amprobe found each ac took about 14.5 amps when running on low fan. Problem is when one is running loaded, and other one starts, load goes way over 30 amps for a couple of seconds. Sometimes it is okay, but most of the time breaker trips. How do you get around this?

 

[Second Chance]

On 12/6/2017 at 7:18 PM, richfaa said:

what we did do when we ordered this 5th wheel was to make sure the  load on the legs were evenly distributed that is one A/C on each leg not both on the same leg etc. We  are nearly always on 50 amps and have never had a load issue on either leg. We do pay for our electric here on our Florida site and we use what we use. 

X2^^. Unbeknownst to us, our rig came from the factory with both ACs on the same 50 amp leg. ("Assume" is a dangerous word, but I can only assume that they were trying to balance with the washer/dryer we don't have on the other leg.) Anyway, we didn't have any problems for the first couple of years. Then, we stayed at a "resort ranch" in east Tennessee that had full hookups with 50 amp power (out in the middle of an absolutely beautiful pasture surrounded by mountains!). The row we were on was having low voltage problems on just one leg - but it happened to be the leg our ACs were on and our EMS kept taking us off-line or the breaker at the pedestal would trip when both ACs were running and the voltage dropped even further. The solution: unplug the rig, pull the breaker panel, switch around some breakers on the buses, and separate the two ACs on separate power legs. It fixed the problem at that location and we haven't had a problem since.

Rob

[jcussen]

Thinking problem was mostly with the park. In rigs with 3 roof airs, good chance 2 are on one leg and 1 on the other. Even though unbalanced and more current on neutral, should work okay. John T., please correct me if I am wrong. Still wondering how Dale runs both ac's at the same time.

[oldjohnt]

1 hour ago, jcussen said:

Using an amprobe found each ac took about 14.5 amps when running on low fan. Problem is when one is running loaded, and other one starts, load goes way over 30 amps for a couple of seconds. Sometimes it is okay, but most of the time breaker trips. How do you get around this?

JC, "how do you get around this"

 

 1) One possibility (others may include solid state starters and control and time delay so two units cant be starting at the same time) is to use an HACR rated circuit breaker (IFFFFFFFF one is available in the size, amperage, voltage and number of poles to fit your panel???? and it may or may not solve the problem as well as solid state dual AC control devices) HOWEVER when designing a branch circuit (at least for residential and commercial use) I FIRST a) calculated the "maximum continuous current",,,,,,,,,,,,,,, and then  I sized the conductors to have a minimum ampacity of 125% of that,,,,,,,,,,,,,,,and then I c) sized the overcurrent protection device (IE Circuit Breaker) to adequately protect the conductors THEREFORE if a circuit actually carried 29 amps it would require a minimum 40 amp rated circuit NOT 30 !!!!!!!!! NOTE this was again for residential and commercial I cant say if its for the RV industry but its still how I would design it regardless. When a fuse versus a mechanical circuit breaker is used they manufacture dual element time delay fuses which would allow short term current surges so a motor or AC unit etc will start and NOT blow the fuse  

40 minutes ago, jcussen said:

Thinking problem was mostly with the park. In rigs with 3 roof airs, good chance 2 are on one leg and 1 on the other. Even though unbalanced and more current on neutral, should work okay. John T., please correct me if I am wrong

 JC, sure on a 50 amp RV two AC units may be on one leg, but remember those are 50 NOT 30 amp legs so they should handle 29 total amps..........  

 

John T LOngggggggggggggg retired power distribution design engineer and rusty on NEC so no warranty, I'm sure they have improved and the code has changed since I retired grrrrrrrrrrrrrrr

[jcussen]

John, I understand this. but if campground has a 30 amp breaker and I do not have a "soft start unit" on my ac's, I do not see how different wiring, or an HACR breaker, will prevent the campground 30 amp breaker from tripping when one ac is running and the other one tries to start, If you know this, please tell me.

If you read the beginning of this thread, you will see I was the first to point out that 50 amp service was actually 50 amps per leg which is why I commented that it was probably a park problem.

 

[Kirk W]

3 hours ago, jcussen said:

Still wondering how Dale runs both ac's at the same time.

It is important to realize that not all RV air conditioners are alike. They come in several different BTU ratings so the higher capacity ones also draw more running current. There are also several different priced units of the same BTU rating and those too vary quite a bit in the run current. Run current for the high-efficiency units is significantly less than for the standard ones. I just did some looking and saw run currents for new units that range from a low of 8a to a high of 13.5a for new, 13,500 BTU units. Some RVs have 15,000 BTU units. Add in the effect of what we call a "soft start" circuit or kit and you can see that the required start and run currents vary significantly. 

Yet another factor is the condition of the circuit breaker that is supplying the power to the two RV air conditioners in question. A new circuit breaker listed as 30a will actually carry around 24a or so when under constant load. The 30a rating is for short periods and there is also a much higher trip point for an instantaneous trip setting.