No matter how big or small the electrical system is for which you are trying to diagnose electrical problems, the process used is basically the same, and the same electrical laws still apply.

Such was the case with a small camping trailer’s electrical system. The 3-year-old, 18-foot trailer is similar to a tiny house, with many of the conveniences of a full-size home. It has a kitchen with a stove, microwave and refrigerator and a dinette area. It has as a toilet, sink and small shower in the wet bath. There is also a TV, radio, USB charging station, ceiling exhaust fan and HVAC unit.

The electrical system can run off battery for a duration that is load-dependent, but it is more typically connected to shore power. The recommended typical power is 30A, 120V. On a two-day trip, a 15A, 120V receptacle in a detached garage provided power with an adapter plug. The circuit breaker tripped on several occasions during the stay.

Upon return, the camper developed other issues. The radio failed to turn on, and, more concerning, four of the 120V AC receptacles didn’t function, including the GFCIs in the kitchen and bathroom, an external receptacle and one in the dinette with the USB ports.

How to fix it

The first step to finding a solution is to understand the electrical system. The user’s manual has very limited information on the system, and no wiring schematic. Owners of similar campers posted use-at-your-own-risk information online that gave some clues, although some of it was misleading. The figure above is a reasonably accurate block diagram of the camper’s various power sources, determined from the available information and a series of V/I/W measurements.

Since the camper is marketed for “boondocking,” it needs to operate in some minimal capacity without external power sources. The 12V, 200 amp-hour battery is the heart of the system. This particular unit has a 2-kW inverter that generates the 120V AC when needed. Some loads are strictly 12V DC driven. The external cabling is 120V AC, 30A, or 15A if used with an adapter. Also included is the 162W solar panel.

Testing began with only the 12V battery as the power source, the DC-to-AC inverter turned off, no shore power and a blanket  over the solar panels. The DC voltage and current were noted as each load was turned on and off, along with the quiescent loading. Solar panels were tested under various sun conditions. Similarly, the inverter was turned on and power measurements made. Finally, the shore power (15A source) was connected and more power measurements made.

Two issues resulted in the breaker trips. The shore voltage level was 110V or lower during the “at-home” tests, due to a heat wave’s impacts on the electrical utility’s distribution system and the air conditioning loads in the house. 

Switching to a dedicated circuit in the garage improved this. But the air conditioner’s load was over 1 kW, leaving little for other operating loads at this reduced voltage. The microwave had a slightly higher load, but only for a short time. Both couldn’t be operated at the same time on a 15A circuit.

The mysterious loss of power at the four 120V AC receptacles was next. Tracing out the wiring determined it went to the kitchen GFCI from a 15A breaker, then the external receptacle, followed by the dinette receptacle and finally the bathroom GFCI. The kitchen GFCI wouldn’t reset, indicating a hard fault that replacing it wouldn’t fix.

While investigating the wires in the external receptacle, it became clear that improperly terminated ground wires had damaged the insulation on the line wire. Repairing it cleared the fault, and all receptacles worked. 

Then, at a campsite, it was found that there was no connection on the line conductor from the external to dinette receptacle. Initially, it was thought to be a failure in the cable, possibly from critters chewing on conductors.

It was determined that the line conductor screw on the dinette receptacle couldn’t connect the wire internally. A new cable and receptacle made the circuit fully operational again, and the trailer owner was a happy camper!

Richard P. Bingham