TLDR:
A generator transfer switch is the device that safely shifts your electrical load between mains power and your backup generator. It’s a legal requirement under AS/NZS 3010 for any standby generator installation in Australia. Manual transfer switches are cheaper and simpler but need someone on site to flip them over. Automatic transfer switches (ATS) detect mains failure and switch over in seconds without human intervention, which is why they’re the standard for any operation that can’t tolerate downtime: refrigeration-heavy retail, healthcare, data, manufacturing, and critical infrastructure.
If you’re scoping a generator for your site, the transfer switch is the part of the install that determines how the whole system actually behaves when the grid drops. It’s also the part most people underestimate.
This article covers what a generator transfer switch is, why it’s non-negotiable from a safety and compliance standpoint, and how to weigh up manual versus automatic changeover for your site.
What Is a Generator Transfer Switch?
A generator transfer switch is the piece of switchgear that sits between your mains supply, your backup generator, and the load (your building’s circuits). Its job is to make sure those two power sources are never connected at the same time.
Why does that matter? Two reasons:
- Safety: If your generator backfeeds onto the mains supply during an outage, it can energise the network downstream of the fault. Linesmen working to restore the grid expect those lines to be dead. Backfeed kills people. A transfer switch makes backfeed mechanically impossible.
- Equipment protection: Connecting two unsynchronised power sources damages the generator, the building’s wiring, and anything plugged into it.
In Australia, AS/NZS 3010 (electrical installations covering generating sets) requires a properly rated and installed transfer mechanism for any standby generator. Insurance, council, and Energex connection requirements all flow from that standard.
Manual Transfer Switches (MTS)
A manual transfer switch is exactly what it sounds like: an isolator that someone physically operates to move the load from mains to generator and back again.
How it works: The mains drops. Someone on site walks to the switchboard, starts the generator, waits for it to come up to voltage and frequency, then throws the transfer switch to “generator.” When mains comes back, the process runs in reverse.
Best for:
- Sites where a few minutes of downtime is acceptable
- Single-site small businesses with someone consistently on the premises
- Worksites, farms, and rural properties using portable generators
- Backup arrangements that are used infrequently
Pros:
- Significantly cheaper than an ATS, both in equipment and installation
- Fewer moving parts, so less to fail
- Simple to operate and maintain
- No control wiring or programming
Cons:
- Useless if nobody’s on site when the outage hits
- Multi-minute outage minimum, even with someone present
- Human error becomes a real risk (wrong sequence, paralleling mishaps, leaving in the wrong position)
- Not suitable for unattended sites or critical loads
Automatic Transfer Switches (ATS)
An automatic transfer switch monitors the mains supply continuously. When it detects voltage drop, phase loss, or frequency deviation outside acceptable limits, it triggers the generator to start, waits for it to stabilise, and transfers the load over. When mains returns and stabilises, the ATS transfers back and shuts the generator down.
The whole sequence typically completes in 10 to 30 seconds, depending on generator type and configuration.
Transition types:
- Open transition (break-before-make). The most common configuration. The load is briefly disconnected during transfer, then reconnected to the new source. Suitable for most commercial applications.
- Closed transition (make-before-break). The two sources are momentarily paralleled during transfer, so there’s no interruption to the load. Used where even a sub-second drop is unacceptable. Requires synchronisation and is more complex to install and certify.
- Delayed transition. The load is disconnected, held for a defined delay (usually a few seconds), then reconnected. Used where motor loads need time to spin down to avoid out-of-phase reconnection damage.
Best for:
- Refrigeration-heavy retail and food service (cold chain protection)
- Healthcare, aged care, medical
- Data centres, server rooms, telco
- Manufacturing with continuous processes
- Fire and life safety systems
- Any site where unattended operation is the norm
Pros:
- Operates without anyone on site
- Switchover in seconds rather than minutes
- No human-error risk
- Can be remotely monitored and managed
- Closed transition options eliminate even brief interruption
Cons:
- Higher upfront cost (equipment, controls, installation, commissioning)
- More components, so more to maintain and test
- Requires periodic functional testing under load
- Programming and commissioning needs a contractor who actually understands the controller, not just an electrician who’s wired one in
Manual vs Automatic Transfer Switch: Side-by-Side
| Factor | Manual Transfer Switch | Automatic Transfer Switch |
| Switchover time | 2 to 10+ minutes | 10 to 30 seconds |
| Requires person on site | Yes | No |
| Equipment cost | Lower | Higher |
| Install cost | Lower | Higher |
| Maintenance | Minimal | Requires periodic functional testing |
| Best for | Attended sites, infrequent use | Critical loads, unattended operation |
| Risk of human error | Real | Very low |
| Remote monitoring | No | Yes (most modern units) |
Which One Is Right for Your Site?
For most commercial sites, an ATS is the right answer. The reason is simple: the cost difference between MTS and ATS is usually a small fraction of the total cost of the generator install, and the value of removing the human-attendance requirement is significant.
Where MTS still makes sense in commercial environments:
- Sites with permanent on-site staff and tolerance for short outages
- Light commercial premises where the generator is genuinely a “nice to have” rather than a critical asset
- Worksites where the generator is portable, and the transfer switch is part of a temporary arrangement
For residential applications, the picture is different. Most home generator setups are portable units used during cyclones or extended outages, and an interlock kit or small manual transfer switch is often sufficient. Where a home is running critical medical equipment, off-grid solar with generator backup, or a high-value cold chain (commercial freezers, wine collections), an ATS becomes justifiable. (Note: Terawatt’s residential work is limited to EV charger installation. For residential transfer switch work, engage a domestic-focused electrician.)
What’s Involved in Installing a Transfer Switch
A compliant transfer switch installation typically covers:
- Load study: Sizing the switch (and the generator) for the load it has to carry, including starting currents on motor loads
- Switch selection: MTS or ATS, open or closed transition, the right rating and configuration for the application
- Switchboard modifications: Where the transfer switch sits inside or alongside the main board, with appropriate isolation and protection
- Generator interface: Control wiring between the ATS and the generator’s auto-start panel
- Commissioning: Functional testing under load, including simulated mains failure and restoration
- Documentation: Form 16, schematics, operating instructions, and asset register entries
- Periodic testing schedule: Most insurers and standards require functional testing at defined intervals (typically monthly or quarterly under load)
This is not work for a generalist sparky. Get it wrong and the system either doesn’t work when you need it (worst case, during a real outage), or it backfeeds and creates a safety incident.
Frequently Asked Questions
Is a transfer switch legally required for a backup generator in Australia?
Yes. Any standby or backup generator that connects to a building’s wiring requires a transfer mechanism that prevents simultaneous connection to mains and generator. AS/NZS 3010 sets the standard. The only exception is genuinely standalone generators with their own dedicated outlets that aren’t wired into the building’s switchboard.
How long does an ATS take to switch over during a power cut?
Most commercial ATS units transfer in 10 to 30 seconds. The actual time depends on how long the generator takes to start, come up to voltage and frequency, and stabilise. Diesel sets typically take 8 to 15 seconds. For loads that can’t tolerate any interruption, a UPS sits between the load and the ATS to bridge that transfer gap.
Can a transfer switch be retrofitted to an existing generator install?
Yes, in most cases. We assess the existing generator, the switchboard, and the control wiring, and design the retrofit around what’s already there. Sometimes the switchboard itself needs upgrading to accommodate the new switchgear, which is worth factoring into the scope.
How often should a transfer switch be tested?
Functional testing under load every month is the gold standard, and what most insurers expect. Quarterly is acceptable for lower-criticality sites. The test simulates a mains failure to confirm the generator starts, the ATS transfers, and the load runs cleanly on generator power.
What’s the cost difference between MTS and ATS?
The switch itself is usually 3 to 5 times more expensive for an ATS. Installation is also more involved due to control wiring and commissioning. On a typical commercial install where the generator itself is the major line item, the ATS premium is usually 10 to 20% of the total project cost.
Can a transfer switch handle solar, batteries, and generator on the same site?
Yes. Multi-source switchgear is increasingly common as more sites combine solar, battery storage (BESS), and backup generation. The control logic is more complex, but the principle is the same: at any given moment, the load is connected to exactly one source.
Scoping a backup generator or upgrading a transfer switch for your commercial site?
Terawatt provides commercial electrical services across the Sunshine Coast, Moreton Bay, and Brisbane. Gold Master Electricians, Electrical Contractor Licence 84790, operating since 1978.
