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CAUTION
Over our 33 years of Prevost ownership we have had 2 or 3 50 amp breakers on the RV park shore power trip due to a weak or failing breaker. On our current RV site with current draws on the bus at 36 amps on one leg and 24 on the other we tripped the breaker twice so I called the RV park manager who came with an electrician.
When I finally convinced them I was not overloading the circuit which is what is assumed when they see a Prevost they did admit to a fairly frequent 50 amp breaker failure in the RV park so they replaced the failed breaker but they did it with a 60 amp breaker.
I mention this because our cords are sized for 50 amps max per leg and if we accidently exceed 50 amps of current draw we run the risk of damage to the wiring or cords or of starting a fire.
As a rule of thumb we should manage shore power loads to never exceed 40 amps.
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17 Replies
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Jon:
Would setting the inverter to 50 Amp fix that possible issue. I ask this question owning a Featherlite where everything is run through the inverters unless you manually switch the rotary switch specifically to shore or gen instead of normal position.
Chuck
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I moved a couple of breakers around a few years I tried to balance power out a little better, Leg # 1 has the front AC and the rear AC and the electric side of Aqua Hot 12 amp’s. The AC’s the 2 electric toe kick heaters, Micro wave are some of my high draws, None of them go through the inverter’s. I moved the Aqua hot electric to leg #2, I tried to think about it toe kick heaters not used much leg #2. warm weather Is where we go to more so AC’s are used more then heaters. When we 1st bought bus I bought a Dyson electric heater and I wired in to Leg #2 to main fuse box a 20 amp breaker-romex-receptacle just for heater. When I was doing RV repair I sent in quite a few inverters for repairs on the contactors. The tech from a Zantrex repair shop told me is electric heaters plugged in to a plug that goes through the inverter kills the contacts in the inverter, Is repairable but a pain and costly. I put a Receptacle in bath for my wife’s hair dryer also.
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Induction start up loads are the “breaker killer” when you are already drawing significant amps through either leg. Induction loads are from starting up devices which have a high magnetic field required to get them to begin doing work for you (think electric motors, some induction cooktops and some microwave ovens). The startup amperage can be several times the running amperage if only for a short time. Air conditioners are the most common but not the only induction loads we need to be concerned about, especially when on less than 100 nominal amp power plugs. Soft start devices that wire into the A/Cs themselves will help dampen the startup amp load on that one device (usually by 50% to 80%) by ramping up the draw rather than having it come on all at once.
Newer devices are coming to market that may be able to provide soft start capability for all the induction loads instead of just the ones with a soft start device installed internally. These plug in between the power pole and the coach. They won’t alter the running amp draw, only the starting amp draw, but may help you manage situations where the breaker is old/weak or where you are forced to plug in to less than 100 amp outlets.
I have another article coming out in Bus Conversion Magazine about these devices in upcoming issues.
Jerry
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The coach will protect itself with your in house 50 amp breakers. Even if you plugged into an oversized breaker the coach breakers would trip when you exceed the 50 amp limit (somewhere a bit less than 50 if it’s for an extended period).
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Bill, that is what i was thinking, My Country Coach has breakers at the end of the Shore cord, and the output leg of my generator. This would trip before it got to anything to cause damage. Maybe Liberty does it differently?
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Chuck and others, I only know on my Liberty if my current draw exceeds 50 there is no 50 amp protection other than the 50 amp CB at the shore power. I cannot speak to other conversions, but my point is simple that I was surprised when an electrician replaced a 50 amp breaker with a 60 amp knowing my power cord had #6 wires rated for up to , but not exceeding 50 amps. When I am on generator I have 70 amp breakers.
I manage my power having been in the business of supplying shore power pedestals not only under the Jamestown Advanced Products brand, but other brands we private labeled such as for Siemens and Murray among others. I know as long as I remain at 40 amps per leg or below the breaker will not likely trip and that an inrush, such as a recycling A/C unit will not trip the breaker. My reason for posting is those not managing power and find an RV park putting in larger breakers than allowed can have potential shore power cord damage or worse a fire.
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FYI…..Marathon Coaches all have a 50A breaker between the street service and the transfer switch. I have scratched my head for years why they did that, but must have been a forward thought….
Also….the RV Resort I own in in Florida has started installing 60A breakers for all their sites. Wires are properly sized for the 60A. I have heard rumors that the new Featherlights are spec’d at 60A for shore power.
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TNJET, The spot I am in currently, here in Northern CA has 60 amp breakers on the pedestal. I have never looked at this before.
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As long as your loads do not exceed 50 amps on the #6 wire power cords there is no issue.
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I find it hard to believe that any RV manufacturer would not have 50 amp breakers built into the electrical system. This would violate pretty much every legal electrical parameter for any habitable structure. You might want to look again. There must be a dual 50 amp breaker somewhere in the coach. Otherwise, the manufacturer would be liable for any damage done to your coach downstream from the inlet. Imagine a house without breakers! You have something like a gazillion volts coming into your house but the service is limited by the breakers. The same thing is true for your coach.
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Regardless of what a converter might do regarding circuit protection using a 60 amp breaker in a UL listed temporary power outlet is not only a violation of the certification of the outlet because the receptacles are rated only for 50 amp per leg, but our power cords are designed for 50 amp max.
Each converter does its own thing, so each coach owner needs to understand what their converter has done for electrical circuit protection. I can say this based on decades of Prevost forums I have never ever read of an owner tripping a 50 amp breaker in his coach, but many posts regarding tripping shore power CBs. I find and believe that to mean the converters have special CBs or it is an incredible circumstance where only shore power breakers trip.
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Couple things. The NEMA plug is rated for 50amps but the wire is likely 6 gauge which can handle 55amps or so. Now if using something more than 2 hours you’re only allowed to use 80% of its rating so legally you can only draw 40amps from a 50 amp plug. Good inverters will have an option to limit amperage and apply the 80% limit. My Victron does and I can switch it anytime from my phone all the way down to 11.3amps (less if I didn’t have 5000w inverters)
AC units and other inductive devices pull a ton of amps. My Dometic penguins 13.5k that came have a LRA of 52amps and the brisk 15k I’m putting in has a LRA of 64amps. This runs for a few seconds to start the compressor. Can easily trip breakers especially with other loads.
We should all have internal breakers inside the coach on the wiring so even if they have a 60amp breaker and you have a 50amp it’ll be protected at 50amps.
On my coach I have a 60amp breaker for shore on 6ga wire, a 80amp breaker for genny on 4ga wire both going into my Victron inverter rated at 100amps. I then have 4ga wire going to my breaker panel then another 4ga wire going to the 2nd breaker. My inverter is set to 50amps for shore and 80 for genny then only uses 80%. It’ll assist either to 100amps using battery power.
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Excellent post. Very important info, especially during the summer “rally season” when power available from temporary sources like fair grounds can lead to low voltage issues which serves to exacerbate the amp overload issues when everyone on a string tries to start all kinds of induction loads at random times. 120vac air compressors, residential refers, and even 120vac water pumps can also cause these conditions right along side A/C units, some microwaves (especially the “inverter” units), some induction cook tops, etc. All these start up loads can really tax the source electrical system as well as the bus internal electrical system. So, be careful out there!
PS, so far the plug and play soft start device I am testing for the upcoming magazine article is performing well on the 30 amp service available at the fair grounds setting where the rally we are attending is being held. Having only 30 amps available really is dicey for all these large plastic coaches in attendance here. More as I learn more.
Jerry
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Technically a breaker should only be expected to protect a conductor down stream of it. Jon’s original post is correct.
2000 Featherlite H3-45
2024 Jeep Grand Cherokee
Leesburg, FL -
One additional reference point is that not all wire of the same size can safely carry the same amp load. Cheap CCA (copper coated aluminum) wire is at the low amp end of that spectrum and tinned solid copper high strand count marine wire with high temp insulation is at the high amp carrying end of the spectrum. So, the type of wire, the size and the environment in which it is used all determine the size of circuit breaker required. Don’t overlook the importance of gas tight properly set crimps on the wire ends, also.
For our buses the best (and most expensive place) to buy wire used for DC loads is a good marine dealer. For AC loads go to an electrical supply house. The worst place to buy wire for DC loads is eBay, followed by the big box stores and home centers. For AC loads use stranded, rather than solid wire, and avoid wire nut connectors.
Jerry
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