Inverter / Mains Changeover Switch Wiring Diagram (AC Bypass Switch)

Description

This wiring diagram provides a clear, beginner-friendly guide showing how to correctly wire a bypass / changeover switch to safely switch power between an inverter and mains shore power.

The diagram focuses specifically on the AC switching arrangement only, showing how a 3-position changeover switch routes power from either:

• Inverter supply
• Mains hook-up (shore power)

…to a shared output feeding socket circuits or an AC distribution system.

The example shown is based on a Heschen SZW26-20/D202.2 rotary cam selector switch (ON–OFF–ON, 20A, 660V rated), but the wiring principles apply to equivalent changeover switches when correctly rated.

This diagram is suitable for campervans, motorhomes and off-grid AC systems operating between 110–240V.

Common Problem (Why This Diagram Helps)

Many DIY installations incorrectly connect inverter and mains supplies together or rely on unsafe switching methods.

Common mistakes include:

• Backfeeding mains into the inverter
• Feeding inverter output into shore power circuits
• No clear isolation between power sources

These mistakes can result in equipment damage, electric shock risk, or dangerous backfeed into external supplies.

This wiring diagram removes that risk by clearly showing how to correctly isolate and switch between power sources using a proper changeover switch.

Features

• Designed for AC changeover / bypass switch wiring
• Covers inverter and mains shore power switching
• Based on 3-position ON–OFF–ON rotary selector switch design
• Clear input/output wiring layout
• Suitable for 110–240V AC systems
• Simple, visual layout for DIY builders and beginners
• Instant-download PDF wiring diagram

Is This Diagram Right for My Van?

YES – this diagram is suitable if:

• You want to switch between inverter and mains power safely
• You are installing a manual changeover / bypass switch
• You want a clear understanding of how AC source switching works

MAYBE – check first if:

• You are using an inverter with a built-in transfer switch
• You are unsure how your AC system is currently configured

NOT SUITABLE – this diagram is not for you if:

• You need a full AC system wiring diagram including protection devices

➡️ If you’re unsure whether this diagram suits your setup, you can contact Jolly before purchasing for confirmation.

Important Notes

This diagram shows switch wiring only.

It must be integrated into a complete AC system that includes:

• RCD protection
• Circuit protection (MCBs / RCBOs)
• Correct earthing and bonding

Cable types and sizes are not specified in this diagram.

The diagram is provided to demonstrate switching logic and wiring configuration only.

Safety Notes

• RCD protection must be installed where required in accordance with BS 7671
• Cable types and sizes must be selected based on load, installation method, and system design
• All AC work must be carried out competently and tested after installation

Incorrect AC wiring can result in electric shock, fire, or equipment damage.

Author / Designer Reassurance

This wiring diagram has been designed by Jolly Goode, a qualified electrician with over 20 years experience in electrical installation and campervan power systems.

The diagram focuses on safe switching practice, clear understanding of AC systems, and preventing common and dangerous wiring mistakes.

Consultation CTA – Need Help Designing Your System?

If you are designing a full campervan electrical system and need help integrating AC switching, protection devices, or inverter systems, bespoke design support is available.

You can contact Jolly or book a consultation to ensure your system is safe and correctly designed.