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Thread: 50 amp.... Why so big?
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04-11-2021, 09:11 AM #11
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This is often debated; hoping this doesn't spark another debate.
Our 50-amp power is not 240V, it is two legs of 120V at 50 amps per leg and is called "120/240 VAC split phase". The wiring of the park supply (hopefully), the heavy supply cord that you don't like, and the distribution of the power in the trailer are all configured to supply two legs of 120V power at 50 amps per leg. Without modification, you can't get 240V anywhere in the trailer. If you can, something is misconfigured and chances are high that the neutral is seeing about double the current that it is rated for, which will let smoke out somewhere in the circuits.
One CAN measure 240V off the incoming supply by measuring across the two hot legs, but nothing in the trailer uses the two hot legs together. Each hot leg is wired with the neutral, not the other hot leg. Measuring either hot leg to neutral - which is what everything in the trailer sees - will show 120V.
This 120/240 wiring configuration is different from 240V outlets typically required for clothing dryers and welders, for example, which require a true 240V supply.
Your observation that the 120/240V system can deliver 12,000 watts is correct, just not all on one circuit/leg. Your "2 AC's, microwaveable coffee maker" are not usually all running on the same leg for that reason - if they were you'd likely hear a 'click' from the circuit breaker panel.
EDIT: @xrated beat me to the punch above while I was whittling at this post.Mark - 2018 Solitude 310GK - 2017 F-350 diesel SRW short box - Pullrite Superglide hitch
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04-11-2021, 09:31 AM #12
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Its simple - Bigger is Better - right? Think back - how many trailers do you remember over 35' back then? Also back then you got the basics, Bed, hot water, shower, stove and commode. The stove and fridge were small so most folks had a cooler and Colman stove for outside. Now it 2 ac's, microwave, several TV's, stereo. Instant hot water, Residential fridge, large bath, fancy lighting, crock pot or ins-ta pot and many more power hungry gadgets. That why its called Glamping
The need for power has grown. One way to help out on a 30A service with a 50 amp trailer is an extensive solar system with a large battery bank and an a large inverter charges (3000 to 5000 watts) with power assist.
Also RV parks are now charging more for a 50A site.2018 Reflection 150 Series 220RK 5th wheel with 6K axle upgrade. B&W 25K OEM Companion, Steadyfast system, 2022 F350 SRW 6.7 King Ranch 8' bed, Trailer reverse lights, rear spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, and Solar
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04-11-2021, 09:56 AM #13
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I took this for granted since this is how our residential 120/240V is.
The possibility of RV parks being wired with say 480/277 to 208/120 3phase Wye with Neutral service hadn't occurred to me.
It should have since our office building had that service from our local utility.
I remember the mechanics buying an air compressor and arc welder for the shop and they were rated for 240V, not 208V.
So that resulted in me adding a 480V to 120/240V transformer for the shop equipment.- Gene
Kim & Gene
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04-11-2021, 09:59 AM #14
@xrated I agree with everything you said for the most part, except for the part about the RV 50A main breaker being in the middle of the panel. I had the same thought process as that is how my Momentum was setup. When I got my Reflection, both 50A breakers were all the way on the left side of the panel with all the other breakers on the right of those 2 breakers. My initial thought was that GD miswired the panel. I took the cover off and looked at the diagram of the panel, and indeed it was wired correctly. This is a Progressive Dynamics breaker box, not the typical WFCO box that is used. Due to the setup of this box, it is important to look at the wiring diagram if making breaker changes to ensure everything is balanced correctly.
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04-11-2021, 10:01 AM #15
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@xrated and @boyscout both excellent explanations. As I was hoping, this sparked a good conversation about the how and why of RV electrical systems. I should have included the split phase explanation in my OP, but it would have gotten really long.
My point was that even with all of the big glamping loads, we don't come close to actually needing 12kw from two 50 amp legs.Just because you plug in to the 50 amp outlet doesn't mean you need to wire the entire input to the RV at 50 amps. A 30 amp main breaker in the RV panel would be plenty.... reduce wire size reduce weight and on and on. The industry preaches that they do things to save weight but I would much rather save 40 pounds of wire and put that 40 pounds into a heavier chassis or something. Little things like soft starts on the AC's would go a long way to reducing the actual power required. By all means, if you have a 42 foot condo with three AC's and tank less water heaters wire it up with 6 gauge and let it ride. But if you have a 30 ft TT with one AC then put a 50 amp split phase plug on it and a 30 amp main breaker and tone everything down a little bit. Rant over😁
And as somebody mentioned the AC's should be on opposite legs but in my last 5th wheel they were both on the same... had to fix that.
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04-11-2021, 10:30 AM #16
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Yes, I'm sure that there are variations of the "middle of the panel" configuration, but the bottom line is that one half of the main breaker feeds one buss....and the other half of the main breaker feeds the other buss in the panel. And MOST IMPORTANTLY, the buss is configured so the you CANNOT put in a double pole breaker and get 240VAC from the two breaker terminals.
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04-11-2021, 10:38 AM #17
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You haven't met my wife.
Thanks all of you for your great explanations, this is why I like reading the forum, I learn stuff. I don't have clue about phases, but the comment about why the neutral never carries both legs made me realize that each time a power cord has shorted out it was the neutral post that burned up.
Yes we have a one bedroom apartment on wheels with a garage. We are on a 30 amp post this month. In order to make this work we have to be cognizant of what load we are carrying. Even with that we get EMS error messages, PE-4, Low Voltage is common. It tends to happen when something starts up, like the microwave.
When we are on 50 amp service I still mind the load, but 36 amp is about the highest I have seen on the EMS thingy on the post. So I lug my heavy old 50 amp cord around and because of you guys' discussion I now know a little more than I did before.Dallas
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04-11-2021, 10:40 AM #18
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I guess I'm one of "those guys" with the 44' Rolling Condo.....with three A/C units, a fireplace, a Convection/Microwave and of course the 18 cu. ft. RV fridge that is propane/electric, and the 12 gallon water heater.....not to mention being able to install a washer/dryer if I wanted to and be able to plug in a portable 1500W electric heater....so I'm pretty happy with my 50A RV service for the castle. And as far as dividing the A/C load, on mine there is one 15K BTU and one 13.5K BTU on one leg of the 120VAC, then the other leg has the other 15K BTU A/C on it. So it's very common to have all three of them running at the same time....in the hot summer time period. I think that the 50A service has gotten so common, that most people would think that they are getting "shorted" by the trailer manufacturer if they only came with a 30A service. Plus, one the ones with only one A/C but prewired for the second one.....and having that fireplace, water heater, Convection/Microwave, etc.....you still need to have a 50 to service that much equipment.
2016 F350 CrewCab Dually
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2023 Suzuki GSX-S1000 GT+
Excessive Payload is a Wonderful Thing
"If it ain't fast....It ain't Fun"
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04-11-2021, 10:46 AM #19
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My 30amp emc shut down when I reached 30amp. The coffee pot, electric water heater and microwave at the same time reached 30amp.
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04-11-2021, 10:48 AM #20
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Last edited by xrated; 04-11-2021 at 12:49 PM.
2016 F350 CrewCab Dually
2018 Momentum 394M...Heavily Modded!
2023 Suzuki GSX-S1000 GT+
Excessive Payload is a Wonderful Thing
"If it ain't fast....It ain't Fun"
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