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RV Inverter Transfer Switch Installation: How To Guide

Some campers have AC circuits powered by shore power. For RVers who spend most of their time on campgrounds, the need for DC circuits is fairly limited.

However, to continue to use AC appliances when boondocking or off-grid, an inverter is essential. While you could install a separate inverter with dedicated circuits to run the appliances you’ll use when off-grid, you can leverage your existing AC circuits for a slicker solution.

By installing a transfer switch and inverter to the RV’s AC distribution box, you can flip between shore power and the battery supply on demand. Then you only need one set of circuits for your appliances. 

In all likelihood, you’ll use a smaller number of AC appliances when off-grid. Some appliances, like air conditioning units, use massive amounts of energy compared to the size of the battery bank and your ability to recharge them.

You can set up your camper’s electrical system so that the battery bank only supplies your priority AC circuits when off-grid.

Before we get into it, this post is part of our mini-series on power inverters so if you’ve landed on this page but are not yet ready to install your inverter, take a look at our other articles to help get AC power in your camper when off-grid:

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Before You Start 

RV Inverter Transfer Switch Installation
  • You are dealing with AC power and that has the potential to kill. 
  • These guidelines do not replace the need for a qualified electrician but give an indication of the work involved. If you do not know what you are doing, always use a qualified electrician.
  • Always use the correct wire size specification and color scheme conventions as dictated by your local electrical regulations.
  • Never cross-connect any wires between the live, neutral, and earth connection points. Live should connect to live, neutral to neutral, etc.
  • Route cables in conduit and avoid laying them in a way where they could be crimped under paneling or wear on corners. This could lead to unprotected bare wires creating a fire and shock hazard.
  • Always route AC cables in separate conduits and well away from your DC circuits.
  • Make sure you’ve bought a compatible inverter.
  • Always disconnect the battery bank power supply before installing the inverter.
  • Always use the correct size wires and fuses.
  • Always read the manufacturer’s installation instructions before you begin. They know their products better than we do, so their instructions always trump ours.
  • Be clear about the grounding/earthing requirements for your inverter adn any other electrical component you’re installing. 

This post provides general information for installing an power inverter only. Installation of an inverter charger, converter, or any other device is not the same. We’ll provide detailed instructions for those devices in separate articles.

Although AC electrical systems are indeed dangerous, learning about your camper’s electrical system isn’t. We’ve written the Campervan Electrics Handbook to help all RV and camper owners understand their systems. 

It’s perfect for anyone converting a camper from scratch, or upgrading parts of an existing setup. And with an entire section dedicated to troubleshooting, it’s also a perfect book to have on hand when you encounter problems and do your regular maintenance routines.

Tools & Materials Needed To Install An Inverter Transfer Switch

There are a few tools you’ll need to safely install an inverter: 

  • Multimeter: To confirm the electrical supply is off, you have correct voltage, cable continuity, and general electrical troubleshooting. Check out our post on how to use a multimeter – it’s not as complicated as it looks.
  • Megohmmeter or Earth insulation tester.
  • Wire strippers:  to remove the plastic sheath off the wire neatly.
  • Heat shrink & heat gun:  to finish connections and terminal joints.
  • Terminal crimping tool: to attach connectors to the wire terminals.
  • Drill: to drill holes to fix the inverter securely in place.
  • Selection of screwdrivers: to fix and secure terminals and wires in place
  • Cable ties or cable clips: to help secure cable runs.
  • ANL fuse holder & fuses
  • Correctly sized wire (red for positive and black for negative)
  • Ring connectors: correctly sized for the wire and connection posts 
  • Pin connectors: to finish the wire ends neatly before connecting them to a screwed terminal 

RV Inverter Transfer Switch Installation Diagram

RV Inverter Transfer Switch Installation

How To Install An RV Inverter Transfer Switch

If this is an extension to an existing system, you MUST ensure all power to the RV is off. There must be no AC or DC power on the circuits. Disconnect from any shore power and generators and isolate your battery bank before you begin.

  • Step 1: Identify your priority AC circuits. These will be powered by the inverter when you are off-grid.
  • Step 2: Install your inverter, with an AC distribution box with individual circuit RCDs for each priority circuit. This is an example of the wiring diagram looks like:
  • Step 3: If this is not part of an existing system, install your shore power and any non-priority AC circuits with their sockets and RCD breakers. 
  • Step 4: Ensure the system is grounded. Connect the earth points to both the external AC supply earth point AND the vehicle chassis earth point. If you do not understand this, please get a qualified electrician to help.
  • Step 5: Any metal casing panels will need the correct earthing connections too. Check the manufacturer’s installation instructions.
  • Step 6: Remove every RCD from the distribution box and the inverter’s fuse.

When using an inverter and shore power supply to provide power to the same AC circuits, you must install a transfer switch to isolate the different power sources. It must be impossible for more than one power source to supply the circuit at any one time.

The transfer switch must be rated for the AC voltage and the highest current supply of all the independent VAC power supplies – inverter, shore power and or generators. 

  • Step 7: Install the transfer switch in its operating location.
  • Step 8: Connect the priority AC circuits RCDs to the transfer switch output terminals.
  • Step 9: Connect the inverter supply to one branch of the transfer switch’s input connections.
  • Step 10: Connect the shore power supply breaker output to the other transfer switch input connection.

NB remember to connect Live to Live, Neutral to Neutral, and Earth to Earth. Use the Manufacturer’s installation instructions to confirm which is the correct terminal on the switch for each circuit.

  • Step 11: Reinsert the RCD breakers for the priority AC circuits.
  • Step 12: Use a multimeter and megohmmeter or Earth insulation tester to confirm correct continuity and insulation from the earth for the priority AC circuits.

Operate The Transfer Switch To Use The Inverter Supply

  • Step 13: Switch the transfer switch to the position to use the inverter power supply. 
  • Step 14: Insert inverter fuse and assuming it does not fail, switch on the inverter.
  • Step 15: Switch on the main supply breaker for the priority AC circuits and confirm the earth fault test function operates correctly.

If any safety feature on the VAC breakers doesn’t operate, disconnect ALL power and seek professional qualified assistance.

  • Step 16: Switch on the individual RCD or circuit breakers to their ON position.

If any safety feature on the VAC breakers doesn’t operate, disconnect ALL power and seek professional qualified assistance.

Or if the individual RCD or circuit breakers fail to remain in the ON position, disconnect ALL power and seek professional qualified assistance.

  • Step 17: Using a multimeter, confirm each priority AC circuit is supplying power at the correct voltage.
  • Step 18: Connect a small AC appliance to each direct outlet in turn to confirm that it is functioning correctly and that the inverter is also operating correctly.
  • Step 19: Continue to add more appliances in stages confirming the entire priority AC system functions correctly and monitor it to ensure the system is operating as designed.

Operate Transfer Switch To Use Shore Power Supply 

  • Step 20: Switch the transfer switch to the position to use shore power supply.
  • Step 21: Connect the RV to a shore power supply.
  • Step 22: Switch on the shore supply breaker and confirm the earth fault test function operates correctly.
  • Step 23: Switch on the main supply breaker for the all AC circuits and confirm the earth fault test function operates correctly.

If any safety feature on the VAC breakers doesn’t operate, disconnect ALL power supplies and seek professional qualified assistance.

  • Step 24: Switch on the individual RCDs or circuit breakers to their ON position.

If any safety feature on the VAC breakers doesn’t operate, disconnect ALL power supplies and seek professional qualified assistance.

Or if the individual RCD or circuit breakers fail to remain in the ON position, disconnect ALL power supplies and seek professional qualified assistance.

  • Step 25: Using a multimeter, confirm each AC circuit is supplying power at the correct voltage.
  • Step 26: Connect a small AC appliance to each direct outlet in turn to confirm that it is functioning correctly.
  • Step 27: Continue to add more appliances in stages confirming the entire AC system functions correctly and monitor it to ensure the system is operating as designed.

Always follow the manufacturer’s operating instructions when switching between shore power supply and the inverter.