AMF & ATS panel repair, testing and retrofit
A standby generator has one job, and it is not "run". It is to start on its own when the mains fail, take the load, and give it back safely afterwards. The equipment that does that is the part of the installation least likely to have been tested since the day it was commissioned.
Two boxes, not one
The distinction that decides the repair
They are frequently spoken of as one thing and they are not. If the set starts on a mains failure but the load never transfers, the AMF worked and the ATS did not. If nothing happens at all, the AMF never saw the failure. Two different repairs.
Auto Mains Failure
AMF — the intelligence
- Watches the mains and decides that a genuine failure has occurred
- Waits out its start delay, cranks the engine, lets it warm up, signals the transfer
- On the mains returning: waits out the return delay, transfers back, runs a cooling-down period and stops the set
- On most modern sets this function lives in the genset controller rather than a separate panel
Automatic Transfer Switch
ATS — the muscle
- The switching device that actually moves the load between mains and generator
- Mechanically and electrically interlocked, so the two sources can never be connected together by accident
- Contactors or motorised breakers, their control supply, the interlock and the transfer signal
- Where "the set started but nothing came back on" almost always lives
What we are called to
Changeover faults
- The mains fail and nothing happens. Mains sensing, the controller's mode, control fuses, the start signal wiring, or a configuration someone changed and did not record.
- The set starts on manual but not on auto. Almost always mains sensing or mode selection rather than an engine fault.
- The set starts but the load does not transfer. ATS contactor or motorised breaker, its control supply, the interlock, or the transfer signal.
- The load transfers and then trips. Load step too large for the set, a fault downstream, or protection settings that do not suit the installation.
- The changeover does not return to mains when the supply comes back — or returns too soon and drops the load again on an unstable supply.
- Contactor or breaker mechanism failure. Burnt or welded contacts, a seized mechanism, a failed motor operator, or an interlock defeated at some point.
- Nuisance changeovers on a supply with brief dips, where the sensing settings are wrong for the site rather than the equipment being faulty.
- Corroded, loose or overheated terminations — in this climate a leading cause of both intermittent faults and outright failure.
- An obsolete controller with no spares, which is a retrofit conversation rather than a repair.
- A latched shutdown sitting underneath the lockout, which has to be read before anything is reset — see generator locked out.
Controller and AVR faults on the genset side sit on control panel diagnostics and AVR repair.
The only thing that proves it works
A simulated mains failure, recorded
A visual inspection proves nothing about a changeover. The test is run under controlled conditions with the site's agreement, and every result is written down — because "it was tested" is worth nothing to an auditor without the figures.
- Agree the windowConfirm the set is fit to run and the site can accept a transfer, and who is informed.
- Drop the mains at the sensing pointRecord the time to detect, the start delay, the crank and the start.
- Warm-up and transferRecord the warm-up period and the time to transfer.
- The load transfer itselfVoltage and frequency dip on load acceptance, and how quickly each recovers.
- Hold on loadLong enough to prove the set is stable rather than merely running.
- Restore the mainsReturn delay, transfer back, cooling-down run and shutdown.
- Read the logAlarms raised and cleared, and the controller's event log against what actually happened.
- Then compared, then adjusted
Each timing is measured against how the site needs it to behave, and changed if it does not.
- A separate question
Whether the set will actually carry the building is not what this test answers — see load bank testing.
- Interlocks are a safety function
An ATS is the device that stops the generator being connected to a live mains supply, and the mains to a running generator. Interlocks bypassed, links fitted "temporarily", or a manual changeover left in an intermediate position are all things we find, all things we report to you in writing, and none of them things we leave.
Retrofit and upgrade
Two situations that come up repeatedly
Situation one
Manual set, automatic requirement
An older set with a manual changeover, on a site that now needs unattended standby. Fitting an AMF-capable controller, mains sensing, an automatic transfer arrangement and the engine interface converts it — usually far cheaper than replacing a mechanically sound set.
Situation two
Obsolete controller
When the module is no longer supported and spares no longer exist, repair is a delaying tactic. A current controller restores the function and generally improves it — better event logging, better protection, and readable alarms instead of a code nobody can look up. The work is in the interfacing and the configuration rather than the box.
With a simulated mains failure and a recorded result, so you see it work before we leave. See generator installation and commissioning for the rest of what that involves.
Common questions
Changeover panels, answered
How often should an AMF or ATS panel be tested?
At least annually with a genuine simulated mains failure, and more often where the site's obligations or its risk demand it. A monthly off-load engine test start proves the engine runs; it proves nothing about the changeover, which is the part that actually failed in most of the stories customers tell us.
My generator starts when the mains go but the power never comes back on.
The AMF has worked and the transfer has not. Look at the ATS — its control supply, the contactor or breaker mechanism, the interlock and the transfer signal. It is a common fault and it is usually repairable rather than a replacement.
Can you fit an AMF panel to an old manual generator?
Yes, where the set is mechanically sound and its engine will accept remote start control. It is a retrofit rather than a repair, and it is commissioned with a simulated mains failure so you see it work before we leave.
Do you work on the transfer switch itself?
Yes — contactor and motorised breaker mechanisms, control circuits, interlocks, terminations and timing. Where a switching device is genuinely at end of life we will say so rather than repeatedly servicing it.
Can testing be done without disrupting the site?
The test needs a real changeover, so a short interruption is part of it. It is planned with you for a window that suits the building — and the alternative, finding out during an actual outage, is not really an alternative.
When was your changeover last proved?
Send the set details, the controller and panel type, and when the changeover was last tested on a simulated mains failure. If the answer is "we are not sure", that is the reason to book one. Regular proving can also be built into scheduled maintenance and AMC cover.