120 Volt Shore Power Repair for Motorhomes and Fifth Wheels
Written by RV Systems Lead, RV Systems and Electrical Lead, OCRV Center. Reviewed by Claims Coordinator
In shortShore power faults live in the inlet, the transfer switch and the pedestal, not in the coach breakers. Alternating current work is billed at $260 per hour, $285 to $5,500+.
What does 120 volt shore power repair cover on an RV?
Shore power repair covers everything between the campground pedestal and the coach outlets: the inlet, the cord, surge protection, the automatic transfer switch, breakers and ground integrity. Rancho Santa Margarita owners bring these units to Yorba Linda because a hot skin fault is not something to keep testing in a campsite.
- A 50 amp service is two 120 volt legs, not one 240 volt supply
- Most no power complaints stop at the transfer switch contacts
- Reverse polarity and open ground come from the pedestal, not the coach
- Burnt inlet pins come from a loose plug, not from too much load
- Price range
- $285 to $5,500+1 to 22 labor hours at $260 per hour
- Labor rate
- $260 per hourMechanical and electrical department
- Typical turnaround
- 1 to 5 shop daysInlet and transfer switch parts are usually stocked or next day
- Written estimate
- $150Credited in full against an authorized repair
- Services tested
- 30 amp TT-30 and 50 amp NEMA 14-50Both legs loaded and balanced before release
Last verified
Shore power problems have a habit of looking like appliance problems. The microwave quits, so the owner buys a microwave. Then the coffee maker on the same circuit does the same thing, and only at one campground. The appliances were never the issue. Something between the pedestal and the panel was.
This side of the coach carries enough current to start a fire and enough potential to hurt somebody who is standing on wet grass with a hand on the entry door. We treat it accordingly. Nothing on this page is a job we encourage an owner to work through with a test light in a campsite.
Shore power problems owners notice first
The most common opening line is that half the coach works. Roof air runs, the microwave is dead, and everything came back to life the moment the generator started. That pattern is close to diagnostic on its own, because the generator and the pedestal feed the same panel through different paths, and the only device that chooses between them is the transfer switch.
The second pattern is location dependence. Everything works at home and something specific fails at one park. That points upstream. Campground pedestals age badly, get backfed by rigs with bonding faults, and occasionally get rewired by somebody who reversed a hot and a neutral. A coach cannot be repaired into immunity from a bad pedestal, but it can be protected from one.
- Works on the generator, fails on shore power
- Fails at one specific park and nowhere else
- A breaker holds until a second compressor tries to start
- Discoloration or a melted rim on one inlet blade
- Any sensation of current when touching the coach body
30 amp and 50 amp service are different animals
A 30 amp connection is one hot leg through a TT-30 receptacle, and it gives the coach roughly thirty six hundred watts to work with. That is a single roof air and not much else. A 50 amp connection is a NEMA 14-50 carrying two separate 120 volt legs, which is why people who describe it as 240 volt service get confused about what their appliances are seeing. Nothing in a standard RV runs on 240.
The practical consequence is balance. A coach with twelve thousand watts available can still trip a leg if both air conditioners and the water heater element ended up on the same side of the panel. We see this most often after a previous repair where somebody moved a circuit to the nearest open breaker slot without thinking about which bus bar it landed on.
| Service | Configuration | Working capacity | Common failure |
|---|---|---|---|
| 30 amp | One hot leg, TT-30 receptacle | About 3,600 watts | Overload trips when a second large load starts |
| 50 amp | Two hot legs, NEMA 14-50 | About 12,000 watts | One leg trips while the other sits nearly idle |
The transfer switch is the part nobody thinks about
Every coach with a generator has a device that decides which source feeds the panel, and it lives in a bay compartment where nothing draws attention to it. The contactor inside makes and breaks a large current, sometimes under load, and it does that every time a generator starts or a cord gets plugged in. Contacts pit. Eventually one set welds partly closed or stops closing at all.
The failure signature is asymmetry. Both legs are present going in and only one comes out. Owners read that as an appliance fault because the affected circuits are scattered across the coach with no obvious relationship, when in fact they simply all sit on the same leg. Testing takes minutes once someone thinks to open the cover, which is why we do it early.
Before you proceed
A transfer switch that chatters instead of latching is arcing repeatedly inside a sealed box. That is a heat event in progress. Stop using shore power and generator power alternately until the unit has been opened.
GFCI trips, open grounds and reverse polarity at the pedestal
A ground fault device is doing its job when it trips. It compares current going out against current coming back and opens when the two disagree by a few milliamps, because that difference is leaving through a path it should not be using. In an RV the usual culprit is water: a heated hose connection in the wet bay, an outdoor receptacle after a storm, or a bay light with a compromised gasket.
Reverse polarity and an open ground are different animals because they usually are not the coach's fault at all. A three light tester at a coach outlet reports the condition, and a check at a second known good source tells us whether the fault travelled with the unit. When it stays at the pedestal, we document the reading and hand the owner something concrete to give the park rather than a vague complaint.
- Test the coach outlet with a polarity tester at a verified shop source
- Repeat at the reported pedestal condition to see whether the fault follows
- Isolate downstream branches to locate a genuine leakage path
- Replace the affected device and re test with the wet bay wetted down
Hot skin voltage and why we stop the job to chase it
Hot skin is what happens when the coach body finds itself at a potential different from the earth under it. It is caused by an open ground somewhere in the path combined with any small leakage inside the unit. Nothing about the coach behaves strangely. The lights work, the air runs, and the only sign is a sensation when a person bridges the body and the ground at the same time.
That sensation depends on how wet the soil is and what shoes somebody is wearing, which means the same fault can be unnoticeable one week and dangerous the next. We measure body to earth potential on every alternating current job that comes through, whether or not anyone reported feeling anything, and a coach reading potential does not leave until the ground path is proven.
What shore power work bills out at
Alternating current work runs through the mechanical and electrical department at $260 per hour. A wet bay receptacle swap with a re test is a short visit. Replacing an inlet, a cord end, a transfer switch and rebalancing a fifty amp load center across both legs is a substantially larger scope with parts on every step, and the range on this page reflects both ends honestly.
Parts carry standard markup and sales tax applies to parts and materials while labor is untaxed. A written repair estimate is $150 and that amount comes back off an authorized repair in full. On jobs over two thousand dollars a deposit applies at authorization, which we state at the estimate rather than at pickup.
On cost
If testing shows the fault lives at the campground pedestal and not in the coach, the visit ends at diagnostic time. We would rather send a unit home with a documented reading than invoice a repair that fixes nothing.
Surge protection, pedestal damage and your carrier
A hardwired energy management system sits ahead of the transfer switch, watches voltage and polarity continuously, and opens the circuit before a bad pedestal reaches the coach. It is the one component on this page that prevents damage rather than repairing it, and units that have one rarely show up here with a cooked converter or a dead roof air control board.
When a surge or a park wiring fault does take out appliances, coverage turns on documentation written before parts come off. Fault codes stored in the protector, the state of the inlet and the affected boards all matter, and once they are in a bin they stop being evidence. We photograph and record at teardown on every alternating current job for exactly that reason.
What is included
- Source side and coach side isolation
- We establish whether the fault travels with the coach or stays at the outlet before opening anything, which keeps us from rebuilding a healthy load center.
- Transfer switch inspection under live switching
- The unit is watched through several source changes with both legs metered, because a contactor that fails intermittently will hold once and drop on the third cycle.
- Inlet, cord and adapter examination
- Every connection point in the chain gets checked for heat damage and fit, including the adapters an owner has been using.
- Ground and bonding verification
- Continuity from the coach chassis through the cord to earth is confirmed, and any hot skin potential is measured and recorded.
- Leg balance measurement on 50 amp coaches
- Both hot legs are clamped with real loads running and branch circuits are redistributed if one side is carrying the coach.
- Surge and EMS installation or replacementwhere applicable
- Hardwired protection is fitted ahead of the transfer switch where an owner wants it.
How the work runs
Test at a known good source
1 hour
The coach is connected to a metered shop outlet with verified polarity and a solid ground. If the complaint disappears, the problem was at the campground and we say so plainly rather than selling a repair the coach does not need.
Meter the inlet, cord and transfer switch
1 to 3 hours
Voltage is read at the inlet lugs, through the cord under load, and on both sides of the transfer switch while the source is changed several times. Heat damage and contact condition are inspected with the cover off.
Verify ground integrity and check for hot skin
1 hour
Continuity is confirmed from chassis through the cord to earth, and a reading is taken from the coach body to a driven reference. Any measurable potential stops the rest of the job until it is resolved.
Repair, replace and rebalance
2 to 14 hours
Failed inlets, cords, switches and breakers are replaced with rated parts. On 50 amp coaches the branch circuits are redistributed so the large loads sit on opposite legs rather than fighting each other.
Load test both legs and release
1 to 3 hours
Air conditioners, the water heater element and the converter all run together while both legs are clamped and the transfer switch is cycled. Readings go in the file with the corrected panel schedule.
What this costs
$285 to $5,500+
1 to 22 labor hours at $260 per hour, mechanical and electrical.
- Parts at $100 or less carry 100 percent markup. Parts over $100 carry 35 percent. Special order parts require a full non refundable deposit at order.
- Sales tax of 7.75 percent applies to parts and materials. Labor is not taxed.
- A 50 percent deposit is taken at authorization on any job over $2,000, with an additional 25 percent when parts arrive on any job over $10,000. Final balance is due at pickup.
- A single GFCI replacement in a wet bay sits at the bottom of this range.
- A load center rebuild with a new inlet, cord, transfer switch and hardwired EMS sits at the top.
- Parts carry standard markup and tax applies to parts and materials, not to labor.
How estimating is billed
- Written repair estimate: $150, credited in full against an authorized repair.
- In depth diagnostic, scan and programming: $285 per hour, one hour minimum, credited in full against an authorized repair.
- In shop pre purchase inspection: $400 to $1,200 depending on unit size and systems count.
- Insurance walk ins are accepted during posted hours. All inspection and estimating work is performed in shop at the Yorba Linda facility.
What you will notice first
- The coach runs fine on the generator but half the outlets are dead on shore power
- A loud clunk from a bay compartment every time the power source changes, or no clunk at all
- The surge protector displays a fault code and refuses to pass power at one specific park
- A breaker trips only when the second air conditioner tries to start
- The bathroom outlet trips its test button within minutes of plugging in the heated hose
- Brown discoloration or a melted ring around one pin on the 50 amp inlet
- A faint tingle when touching the entry handle and the ground at the same time
- Lights flicker and appliances cycle when a neighbor's rig starts its air conditioning
How this fails, and what we do about it
| Failure mode | How we diagnose it | The fix |
|---|---|---|
| Welded or chattering transfer switch contacts | Voltage is present at the switch input on both legs and absent on one output leg with the coach on shore. A chattering unit shows the opposite pattern, cycling as the contactor coil fails to hold. The switch cover comes off and the contacts are inspected for pitting and carbon. | Replace the switch as an assembly. Contact sets on RV grade units are not a serviceable item and dressing a pitted contact buys a few months at best. |
| Overheated inlet pin | Discoloration on one blade with matching damage inside the cord end. Thermal imaging on a loaded circuit shows the connection running far hotter than its neighbors. The cause is almost always a loose fit rather than an overload. | Replace the inlet and the cord end together. Reusing a heat damaged plug on a new inlet transfers the fault to the new part within a season. |
| Open ground or reversed polarity at the source | A three light tester at the coach outlet and a meter reading from the coach chassis to a known earth point establish whether the fault is inside the unit or upstream at the pedestal. Faults that follow the coach to a second known good outlet are ours to fix. | Correct the coach side wiring if the fault is internal. If it follows the pedestal, we document it so the owner can report the site rather than chase a phantom in the coach. |
| Unbalanced legs on a 50 amp service | Clamp readings on each hot leg with a realistic load running. A coach pulling thirty eight amps on one leg and eleven on the other will trip and brown out even though total draw is well inside the service. | Redistribute branch circuits across the two legs at the load center so the large loads are separated, then re measure with both air conditioners and the water heater element running. |
Why it happened
- Transfer switch contacts that welded partly closed after years of switching under load, which leaves one leg live and one leg dead
- A loose set screw at the inlet or in the pedestal receptacle, which builds heat at the connection until the pin discolors and eventually melts its housing
- Pedestal wiring faults at the park, including an open ground, a reversed hot and neutral, or a neutral that is bonded where it should not be
- Load imbalance on a 50 amp coach where both roof air units and the water heater element all landed on the same leg during a previous repair
- A GFCI device protecting a downstream circuit that includes an outdoor receptacle, where moisture in a heated hose connection produces a genuine leakage current
- Cord and adapter abuse, especially a chain of dogbone adapters that adds four connection points to a circuit designed for one
Parts and brands we work with
- Progressive Industries hardwired EMS units and Surge Guard portable protection
- Iota, Parallax, Southwire and Go Power automatic transfer switches
- Marinco and Furrion 30 amp TT-30 and 50 amp NEMA 14-50 inlets
- Square D and Eaton branch breakers used in RV load centers
- Hospital grade and weather resistant GFCI receptacles for wet bay locations
- SmartPlug shore connections on coaches converted away from a twist lock inlet
What not to try yourself
- Using a three prong to two prong cheater plug or clipping a ground pin to stop a nuisance trip. The trip is reporting a leakage path and defeating it puts that current on the coach body.
- Chaining adapters to reach a pedestal that does not match your service. Each added connection is another point that heats, and heat at the inlet is what melts a plug.
- Ignoring a tingle at the entry door because it is faint. Hot skin potential rises with soil moisture and body contact, and the conditions that make it dangerous are weather, not time.
- Sanding a discolored inlet blade and plugging back in. Once the metal has been heat cycled it will not hold tension and the connection restarts the failure immediately.
Which vehicles we do this on
Vehicles we perform 120 Volt Systems on
Diesel PusherDiesel pusher repair means working on a rear engine coach built on a welded Freightliner XC or Spartan rail, with a full body painted fiberglass shell and large basement baysClass A GasClass A gas motorhome repair covers the molded front and rear caps, the vacuum bonded laminated sidewalls, the EPDM roof and the F53 chassis underneathLuxury DestinationLuxury fifth wheel repair covers frame flex at the axle hangers under residential weight, independent suspension components, six point auto level hydraulics and hard flooring at slide thresholdsStandardStandard fifth wheel repair concentrates on the pin box and upper deck welds, the floor at the step up transition, the front cap above the pin and the roof front radius seamSuper CA Super C is a coach built behind a Freightliner M2 106 or International MV conventional truck cabDestinationDestination trailer repair addresses frame flex at the axle hangers on a long light rail, roof ponding because the unit sits level for months, and sidewall bow from slides left extended all seasonI ask two questions before I pick up a tool. Does it happen everywhere, and does it happen on the generator. If a coach is fine on the generator and dead on shore, I have already narrowed it to the cord, the inlet or the transfer switch, and I have not opened a wall yet. The one I refuse to rush is hot skin. If I read potential between the body and my reference, that coach does not go back to the customer that day no matter what else is on the schedule.
Appendix: questions and answers
- Why does my RV work on the generator but not on shore power?
- That pattern points at the cord, the inlet or the transfer switch, since those are the only parts the generator path skips. A contactor with one welded or open contact leaves half the panel live. We meter both legs on each side of the switch while cycling sources.
- Is a 50 amp RV connection really 240 volt service?
- No. A NEMA 14-50 delivers two independent 120 volt legs to the coach, and nothing in a standard RV runs on 240. The distinction matters because tripping usually means one leg is overloaded while the other sits idle, which is a balance problem rather than a capacity problem.
- My bathroom GFCI trips every time I use a heated water hose. Why?
- Because it is detecting a genuine leakage path, usually moisture at the hose connection or in an outdoor receptacle downstream. The device is functioning correctly. We isolate the branch, replace the compromised component and re test with the wet bay deliberately wetted down.
- What causes a tingle when I touch my RV door at a campground?
- An open ground in the supply path combined with small leakage inside the coach leaves the body at a different potential than the earth. Whether you feel it depends on soil moisture and footwear, so a mild sensation is not a mild fault. Stop using the site and have the ground path verified.
- Why did the pins on my 50 amp inlet burn if I never exceeded the load?
- Heat at a connection comes from resistance, not from total draw. A blade that has lost spring tension or a set screw that backed off will run hot at half the rated current. We replace the inlet and the cord end together, since a heat cycled plug ruins a new inlet quickly.
- Does a hardwired energy management system actually prevent damage?
- Yes, and it is the one item here that prevents rather than repairs. Installed ahead of the transfer switch, it disconnects on low voltage, reversed polarity or an open ground before the pedestal fault reaches the converter and appliance boards. Coaches with one rarely arrive here with surge damage.
Open a file on this repair
Tell us the vehicle, what happened and whether a claim is open. We will tell you what the scope looks like and what it takes to get you back on the road.
Or call (949) 799-3387