Direct answer
A changeover device selects which source is connected to an installation or selected loads. A manual changeover requires a person to switch between sources; an automatic transfer arrangement detects source conditions and changes over according to its control logic. The critical safety requirement is not convenience but preventing unintended parallel connection of sources and ensuring the neutral, earthing and protection arrangement works correctly in every operating mode.
Why changeover is more than a switch
Backup power introduces a second source of energy. If that alternate source can energise wiring while the main supply is present, the transfer system must prevent unsafe operating states. ECA(SA) guidance on alternative supplies cites interlocking and three-position break-before-make changeover switching as methods that can prevent unintended parallel operation with the main supply.
| Feature | Manual changeover | Automatic transfer / changeover |
|---|---|---|
| User action | Person selects main / off / alternate | Controller transfers according to configured source conditions |
| Complexity | Lower | Higher: sensing, logic, actuators and control wiring may be involved |
| Best fit | Occasional backup where manual intervention is acceptable | Sites where continuity or unattended transfer is important |
| Failure considerations | Requires someone to be present and know the procedure | Automatic logic and actuating hardware must be maintained and correctly configured |
| Electrical safety | Still requires correct interlock, poles, neutral/earth and protection design | Same requirements plus control-system behaviour and transfer sequence |
What does main – off – alternative mean?
CBI’s QAC residential changeover is a useful example of a manual device: the manufacturer specifies three positions — main supply, alternative supply and off — for single-phase backup-power applications. The off position is valuable because it provides a defined disconnected state between sources when the switch is operated as designed.
What does break-before-make mean?
Break-before-make means the existing source is disconnected before the alternative source is connected. This is an important concept where sources must not be paralleled. ECA(SA) specifically lists a three-position break-before-make changeover switch or a suitably interlocked automatic changeover device among the precautions for switched alternative supplies.
Neutral switching and earth bonding are design questions
Customers often focus on the number of amps on the changeover switch, but alternative-supply installations also depend on neutral and earthing arrangements. ECA(SA) notes that alternative supplies may require an arrangement such as a switch, relay or changeover device to establish the required neutral-to-earth bonding while operating from the alternate source, and that switching of live conductors has to comply with the wiring standard. This is not a universal DIY wiring recipe; it is a reason to have the complete system designed and tested by a competent person.
Questions to answer before buying a changeover device
- What are the two sources — utility and generator, utility and inverter, or another arrangement?
- Is the installation single phase or three phase?
- What current and fault duty must the device handle?
- Which conductors must be switched in the specific system?
- Is manual transfer acceptable, or must the supply transfer unattended?
- Does the inverter or generator already contain transfer functionality?
- How will earth leakage, neutral bonding and protective devices behave on both sources?
- Does the device meet the applicable product standard and manufacturer application?
Do not buy two separate isolators and call it a changeover
Two independent switches can allow unsafe combinations unless the system is specifically interlocked and designed for the purpose. A purpose-built changeover or transfer device provides a defined operating sequence and should form part of an engineered alternative-supply system.
Frequently asked questions
What is a changeover switch used for?
It selects between two power sources while preventing an unintended connection between them when correctly designed and installed.
Is automatic changeover always better?
No. It offers convenience and continuity, but increases system complexity. Manual transfer can be perfectly appropriate where interruption and user intervention are acceptable.
Can a changeover switch be used with a solar inverter?
Yes in some system architectures, but many inverters already include transfer/bypass functions. The entire design must be checked to avoid conflicting transfer devices and incorrect neutral/earth behaviour.
What rating should a changeover switch be?
It must suit the circuit current, poles, voltage, fault duty and application. Do not size it from inverter kW alone.
Can I install a changeover switch myself?
A changeover forms part of fixed electrical and alternative-supply wiring. It should be selected, installed, tested and certified where required by a qualified person.
Technical references and further reading
- ECA(SA): Neutral Earth Bonding Clarified — Alternative supplies, bonding, switching and interlock guidance.
- CBI-electric: QAC Changeover Switch — Manufacturer example: main / alternative / off, 63 A single-phase device.
- CBI QAC data sheet — Detailed product and mounting data.
- Publishing note: product availability and specifications can change. Verify current Whitehouse product pages and manufacturer documentation before publication, purchase or installation.
