I'm still pretty new to RVing and need some guidance on transfer switches. I currently have a Surge Guard 40250-RVC in my 2013 motorhome, but I'm having trouble finding that exact model for replacement. All I can seem to find available is the 40350-RVC model.
My current unit has started making a buzzing sound when connected to shore power. Everything still seems to work fine, but I've heard this might indicate the contacts are starting to fail. I'd rather replace it before it completely goes out and leaves me without power.
Can anyone tell me if the 40250-RVC and 40350-RVC are interchangeable? And should I be concerned about the buzzing, or is there anything I can check before replacing the whole unit?
Surge Guard 40250-RVC and 40350-RVC are interchangeable. Buzzing usually means loose connections - tighten all terminals. If buzzing persists with tight connections, the relay may be failing and unit needs replacement.
Yes, the Surge Guard 40350-RVC is a direct replacement for your 40250-RVC in your 2013 Discovery 40E. The main difference is that the 40350-RVC includes improved contact materials and enhanced surge protection circuitry, but according to manufacturer specifications they share identical mounting patterns and wiring configurations.
However, if your RV has a Surge Guard remote inside, you will also need to change it out to the 40299 as the previous remote does not work with the 40350RVC. The new unit (40350-RVC) reportedly speaks a different protocol as well, which means that the Intellitec and Silverleaf systems would no longer be able to manage the coaches energy usage. Some forums suggest a potential workaround.
But the buzzing you're hearing from your 40250-RVC is indeed a classic sign of contact arcing, which means the relay contacts are wearing out and creating electrical resistance. This buzzing will typically get worse over time and can eventually lead to complete failure or even overheating, so replacing it proactively is the smart move.
The 40350-RVC typically runs around $180-220 depending on your supplier, and since you already have experience with the 40250-RVC installation, this should be a straightforward swap-out job. The upgrade will give you better long-term reliability and improved surge protection for your Discovery's electrical system.
The buzzing sound from your Surge Guard 40250-RVC is caused by the main transfer relay contacts developing pitting and carbon buildup over time. When 50-amp shore power flows through contacts that aren't making perfect connection, they create small arcs that produce that characteristic buzzing or humming sound. This is especially common in RVs that frequently switch between shore power and generator power, as the transfer switching action gradually wears down the contact surfaces.
In your 2013 Discovery 40E, the automatic transfer switch has likely cycled thousands of times over the past decade, and the relay contacts in the 40250-RVC model are known to develop this issue around the 8-12 year mark. The buzzing indicates electrical arcing is occurring, which creates heat and further degrades the contacts. Environmental factors like humidity, dust, and temperature cycling in your electrical bay also contribute to contact deterioration.
While the unit is still functioning now, continuing to operate with buzzing contacts can lead to voltage drops, increased electrical resistance, and potential overheating. In worst-case scenarios, severely degraded contacts can weld shut or create dangerous hot spots in your electrical system.
For this replacement job on your Discovery 40E, you'll need a basic electrical toolkit including wire strippers, a multimeter for testing, and various screwdrivers. Most importantly, you'll need a 10mm and 8mm socket set or box-end wrenches to remove the mounting bolts and electrical connections. Have electrical tape and wire nuts on hand in case any wire connections need refreshing.
Safety equipment is critical for this job - you'll need a non-contact voltage tester to verify power is off, safety glasses, and insulated gloves rated for electrical work. Keep a flashlight or headlamp handy since the electrical bay in your Discovery can be dim. A camera or smartphone is useful for documenting the existing wiring configuration before disconnection.
You'll also want to have some dielectric grease available to coat the new connections and prevent corrosion. Consider picking up a few extra wire terminals if the existing ones look corroded, as this is a good time to refresh those connections as well.
Start by turning off your main breaker at the distribution panel, disconnecting from shore power completely, and ensuring your generator is off and disconnected. Use your non-contact voltage tester to verify no power is present at the transfer switch before beginning work. Test both hot legs of the 240V system and verify readings of 0V on your multimeter between hot conductors and between each hot conductor and ground. Remove the cover panel on your existing 40250-RVC and take photos of all wire connections, noting which wires go to which terminals.
Disconnect all electrical connections from the old unit, starting with the ground wires and working your way through the line and load connections. The 40250-RVC should have multiple connections including shore power hot conductors, generator power hot conductors, load out hot conductors to your distribution panel, neutral, and ground connections. Mark each wire with tape if needed to ensure proper reconnection.
Remove the mounting bolts securing the transfer switch to your electrical bay wall. The 40250-RVC typically uses four mounting bolts in a standard pattern. Install the new 40350-RVC using the same mounting holes - the footprint is identical. Before connecting any wires, apply a thin coat of dielectric grease to all terminal connections to prevent future corrosion.
Reconnect all wires to their corresponding terminals on the new 40350-RVC, ensuring tight connections and proper torque on all terminal screws (refer to manufacturer specifications for exact torque values). Double-check your photos to verify correct wiring before energizing the system. Once everything is connected, restore shore power and test the unit - it should operate without any buzzing sounds and provide proper surge protection indicators according to the unit's display.
If you're not completely comfortable working with 50-amp electrical systems, this is definitely a job for a qualified RV technician or electrician. The voltages and amperages involved in your Discovery's electrical system can be dangerous if proper safety procedures aren't followed. Any uncertainty about wire identification or electrical safety should prompt you to seek professional help.
Call a professional immediately if you discover any signs of overheating around your current transfer switch, such as discolored wires, melted insulation, or burnt smells. These indicate the buzzing contacts may have already caused damage that needs expert assessment. Similarly, if your electrical bay wiring doesn't match standard configurations or appears to have been modified, professional diagnosis is warranted.
Consider professional installation if you discover additional electrical issues during the inspection, such as corroded connections elsewhere in your system or signs of moisture intrusion in the electrical bay. A qualified technician can address these issues comprehensively and ensure your Discovery's entire electrical system is operating safely and efficiently.
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