AMF vs ATS vs DG Synchronization Panel: What Is the Difference and Which One Do You Need?
An AMF panel decides what happens when the mains fails, an ATS decides which source feeds the load, and a DG synchronization panel decides whether two live sources can be connected together. The first two never intentionally parallel two sources. The third exists only to do that. That single distinction — transfer or parallel — sets the architecture, the controller class, the breaker count and roughly the cost.
The practical rule: one standby DG feeding a load it can carry alone needs AMF with a changeover, not synchronization. Two or more DGs that must run at the same time, or any DG that must run alongside the utility, needs synchronization and load sharing, and no amount of AMF programming will substitute. Specify the operating sequence in the RFQ, because the three panel names are used interchangeably in the market and tell you very little on their own.
The Request That Means Three Different Things
A customer says:
“We need an automatic DG panel.”
But that statement can mean three very different things:
- An AMF panel
- An ATS panel
- A DG synchronization panel
All three deal with multiple power sources.
All three may contain automatic controls.
And in some projects, their functions can overlap.
But they do not solve the same problem.
The simplest way to understand them is:
AMF → Detect mains failure and manage standby generator operation
ATS → Transfer the load between two sources
DG Synchronization → Safely operate generators or sources in parallel
Modern generator controllers show this distinction clearly. Manufacturer application guides define AMF as automatic transfer to a genset following mains failure, and list synchronization, load sharing and power management as separate functions belonging to a different class of paralleling controller. Controller product ranges are split the same way: one family for conventional single-DG standby duty, another for synchronization and load sharing.
This guide explains where each system is used and how to choose correctly.
Quick Comparison: AMF vs ATS vs Synchronization
| Feature | AMF | ATS | DG Synchronization |
|---|---|---|---|
| Detect mains failure | Yes | Often | Can |
| Start generator automatically | Yes | Controller dependent | Yes |
| Transfer load between sources | Yes / through changeover | Primary function | Yes, depending on architecture |
| Parallel two DGs | No | No | Yes |
| Share kW load | No | No | Yes |
| Share kVAr | No | No | Yes |
| Dead-bus closing | Basic system dependent | Not primary function | Yes |
| Generator sequencing | Basic standby sequence | Not primary function | Yes |
| Load-dependent DG start/stop | No / limited | No | Yes |
| Peak shaving | No | No | Can |
| Grid parallel | No | Not by itself | Can, if engineered/approved |
| Typical application | One DG backup | Source transfer | Multiple DG / complex power system |
The terminology used by different manufacturers can vary, so the actual functional specification matters more than the panel name.
What Is an AMF Panel?
AMF means:
Automatic Mains Failure
Its main purpose is to monitor the utility supply and automatically start a standby generator when the mains becomes unacceptable.
A typical sequence is:
- Utility healthy.
- Load operates on utility.
- Utility fails.
- AMF controller confirms mains failure.
- DG receives START command.
- Generator reaches acceptable voltage/frequency.
- Load transfers from utility to DG.
- Utility later returns.
- Stability delay expires.
- Load transfers back.
- Generator runs cooldown.
- DG stops.
Manufacturer application guides describe standby-power AMF functionality in exactly these terms: monitor the mains, start the generator automatically on loss of supply, transfer the load, and reverse the sequence when the mains returns.
What Equipment Is Typically Inside an AMF Panel?
Depending on project design:
- AMF controller
- Mains sensing
- Generator sensing
- Mains breaker/contactor
- DG breaker/contactor
- Electrical interlocks
- Mechanical interlock where required
- DG start/stop interface
- Battery charger
- meters
- indication
- alarm
- PLC/HMI if required
A basic AMF system generally assumes:
One normal source + one standby generator
and:
No intentional parallel operation.
AMF Is About Standby Operation
Consider:
Utility → Factory
with:
1 × 500 kVA DG
The DG operates only when utility fails.
No need exists to run:
Utility + DG
together.
No need exists to operate:
DG-1 + DG-2
together.
This is a classic AMF application.
What Does the AMF Controller Actually Measure Before It Starts the DG?
An AMF controller does not simply look for zero volts. It monitors the mains against a window of acceptance conditions, and the DG start command is issued only when a condition stays outside that window for longer than a confirmation delay. The conditions typically monitored are:
- under-voltage on any phase
- over-voltage on any phase
- phase failure or single-phasing
- phase-sequence error
- under-frequency and over-frequency
- voltage imbalance, on schemes that include it
The confirmation delay is what stops the DG from starting on every momentary dip. Typical settings are a mains-failure delay of a few seconds, a generator-start-to-load-transfer window governed by the DG reaching acceptable voltage and frequency, a mains-return stability delay commonly in the range of one to three minutes, and an engine cooldown of a few minutes on no load before shutdown. The actual values must come from the project control philosophy and the DG supplier's engine data, not from another plant's panel.
Our recommendation: treat the mains-return delay as a process decision, not an electrical one. We have had pharma clients ask for a 30-second retransfer delay because the DG diesel cost was visible on a monthly report, then discover that a flickering utility feeder was transferring the plant back and forth several times an hour, each transfer another interruption to the same batch. A three-minute stability confirmation costs a little fuel and saves the batch. On solar and BESS sites the opposite argument sometimes applies, and it is worth asking rather than assuming.
AMF and Synchronization Commissioning: Symptom, Cause, Action
Most problems on these panels appear at commissioning rather than at FAT, because FAT simulates sources while site provides real ones. The table below covers the failures we see most often.
| Symptom at site | Most likely cause | What to check and do |
|---|---|---|
| DG starts on every brief utility dip | Mains-failure confirmation delay set too short, or under-voltage threshold set too tight | Review the under-voltage setting against the actual supply quality and lengthen the confirmation delay; a few seconds is usually enough to ride through a dip |
| Plant transfers back to mains and then straight back to DG | Mains-return stability delay too short for an unstable utility feeder | Increase the return delay, commonly to one to three minutes; confirm the process can accept the extra DG running time |
| DG runs but load never transfers | Generator voltage or frequency not reaching the controller's acceptance window, or a missing DG-healthy feedback | Verify the generator sensing wiring and the acceptance limits before touching the transfer logic; a defective sensing fuse is a common cause |
| Both source breakers can be closed together on a scheme that prohibits it | Electrical interlock defeated or wired through the wrong auxiliary contact | Prove the interlock by attempting the forbidden operation; mechanical interlock must back up the electrical one, not replace it |
| Incoming DG breaker fails to close onto a live bus | Phase-angle or frequency permissive never satisfied, or phase sequence reversed at the DG side | Confirm phase sequence first, then the governor and AVR interface; a reversed sequence will never synchronize regardless of settings |
| Two paralleled DGs share kW unevenly | Governor droop or speed reference mismatched between machines | Compare the governor settings and load-share references machine to machine; this is engine tuning, not panel logic |
| Two paralleled DGs share kW correctly but circulate current | Excitation and AVR settings mismatched, so kVAr is unbalanced | Check the AVR droop and voltage references; kW is the engine's job, kVAr is the AVR's |
| First DG will not close after a total blackout | Dead-bus closing permissive not enabled, or two controllers each waiting for the other | Verify that exactly one machine holds the dead-bus closing priority at a time |
| Load shedding does not release after capacity is restored | Load-restoration logic missing or hysteresis set too narrow | Load shedding and restoration must be specified as a pair, with a deliberate delay between them |
We work through this list during in-house FAT wherever the source conditions can be simulated, and hand the rest to the site team as a written commissioning sequence. Governor and AVR tuning cannot be completed in a factory without the actual engines.
What Is an ATS?
ATS means:
Automatic Transfer Switch
An ATS is fundamentally a source-transfer device/system.
IEC 60947-6-1:2026 applies to transfer switching equipment used to transfer a load between power sources for continuity of supply and energy-management purposes, at voltages within its specified LV scope.
The ATS asks:
Which source should currently supply the load?
For example:
Source 1 = Utility
Source 2 = Generator
or:
Source A Transformer
Source B Transformer
ATS Does Not Automatically Mean Generator Control
This distinction is important.
A purpose-built ATS may:
- monitor both sources
- transfer the load
- send a generator-start contact
But its fundamental job remains:
source transfer.
The generator itself may have a separate controller handling:
- engine start
- engine protection
- warm-up
- cooldown
- shutdown
Therefore:
AMF describes a broader standby-generator operating function, while ATS specifically describes source-transfer functionality.
In many commercial systems, the two functions are packaged together.
AMF and ATS Can Overlap
This causes market confusion.
Suppose a panel contains:
- mains sensing
- DG start contact
- two interlocked MCCBs
- automatic transfer logic
One supplier may call it:
AMF Panel
Another may call it:
ATS Panel
Another:
AMF Cum ATS Panel
All could be describing a similar practical architecture.
Therefore an RFQ should not rely only on the panel name.
Define the sequence.
What Is a DG Synchronization Panel?
A DG synchronization panel is required when two or more generators—or a generator and another energized source—must be electrically paralleled.
For a generator to close onto a live bus, the system must coordinate conditions such as:
- phase sequence
- voltage
- frequency
- phase angle
After connection, generators must then share load.
Paralleling controllers exist for precisely this purpose: they synchronize multiple generators so the machines operate as one power system with balanced load sharing. Published controller specifications for this class of device list automatic synchronization, dead-bus closing and governor and AVR interfaces as standard functions — none of which appear on a basic AMF controller.
Synchronization Is Not the Same as AMF
Imagine:
2 × 1000 kVA DG
The plant requires:
1500 kW
One DG alone cannot carry the load.
Both generators need to operate simultaneously.
Now the system must:
- Start DG-1.
- Close DG-1 onto dead bus.
- Start DG-2.
- Synchronize DG-2 to Bus.
- Close DG-2 breaker.
- Share kW.
- Share kVAr.
- Continuously balance load.
A normal AMF panel does not perform this complete function.
A synchronization/power-management system does.
Work the numbers before deciding, because the boundary is often closer than people expect. Two 1000 kVA DGs at 0.8 power factor give roughly 800 kW each. A 1500 kW demand therefore needs both machines and cannot be met by one, so synchronization is unavoidable. But if the essential load during a mains failure is 700 kW and the 1500 kW figure is the full connected demand including non-essential air conditioning and workshop loads, a single DG with a clearly defined essential bus is cheaper, simpler and easier to maintain. This is the question we raise at clarification stage on almost every multi-DG enquiry: is the 1500 kW an emergency load or a total load? Splitting essential and non-essential distribution in the PCC has saved clients an entire generator more than once.
Synchronization Happens Before Breaker Closing
For an incoming generator to connect to an energized bus:
- phase sequence must be correct
- voltage must be within approved limits
- frequency must be sufficiently matched
- phase-angle difference must be acceptable
Only then should the generator breaker close.
Dedicated generator controllers perform automatic synchronization and interface with speed governors and AVRs to achieve this.
Load Sharing Happens After Synchronization
After both DG breakers are closed:
Synchronization is finished.
Now comes:
Load Sharing
The two important quantities are:
kW — Active Power
Primarily influenced by:
Engine / Governor
kVAr — Reactive Power
Primarily influenced by:
Excitation / AVR
Modern generator controllers explicitly support digital load sharing and VAr sharing.
AMF vs DG Synchronization Example
Case A
1 × 500 kVA DG
Utility fails.
DG starts.
Load transfers.
Best architecture:
AMF / ATS
Case B
3 × 1000 kVA DG
Two or three DGs need to run simultaneously according to plant demand.
Best architecture:
DG Synchronization + Load Sharing + Power Management
What Is Dead-Bus Closing?
After a total blackout:
Bus voltage = 0
The first generator does not need to synchronize to an energized bus.
It needs permission to:
close onto dead bus
and energize it.
After that:
DG-2, DG-3 etc.
must synchronize to the live bus before closing.
Dedicated synchronization controllers provide dead-bus closing functions.
AMF Does Not Mean DG-to-Grid Parallel Operation
Another common misunderstanding:
“If AMF panel has automatic transfer, can DG and mains run together?”
Normally:
No.
A conventional AMF scheme prevents intentional parallel operation between utility and DG.
For grid paralleling, the system requires dedicated:
- synchronization
- protection
- import/export controls
- utility/interface requirements
depending on the project.
ATS Can Be Open or Closed Transition
A normal open-transition ATS operates:
Source A OPEN
then:
Source B CLOSE
A closed-transition ATS can intentionally create a controlled period of overlap/parallel operation when the sources are suitably synchronized.
IEC 60947-6-1:2026 explicitly includes closed-transition automatic transfer switching equipment within its scope.
Closed transition therefore requires significantly more engineering than an ordinary AMF changeover.
AMF vs ATS vs Synchronization — Application Examples
Small Factory With One DG
Recommended:
AMF / ATS
Hospital With Utility + Standby DG
Often:
ATS/AMF architecture
with appropriate redundancy.
Factory With Four DGs
If generators need simultaneous operation:
Synchronization Panel
Data Center With Multiple DGs
Likely requires:
- synchronization
- generator sequencing
- load sharing
- power management
- load shedding
rather than basic AMF only.
Utility + DG Peak Shaving
Requires:
Synchronization / Grid Parallel Control
not basic ATS.
Power Management Goes Beyond Synchronization
A sophisticated multi-DG system may automatically decide:
How many generators should run?
For example:
Low load:
DG-1 only
Medium load:
DG-1 + DG-2
High load:
DG-1 + DG-2 + DG-3
When load reduces, one generator can be:
- unloaded
- breaker opened
- cooled down
- stopped
Power-management functionality in paralleling controllers specifically includes automatic starting and stopping of sources and optimisation of the number of running generators against actual demand.
What Happens if One DG Trips?
This needs to be part of the operating philosophy.
Possible response:
- Running generator trips.
- Remaining DGs take available load.
- Standby DG receives start.
- Non-essential load may be shed.
- New DG synchronizes.
- Capacity restored.
- Shed load restored gradually.
A basic ATS cannot perform all of these functions.
AMF vs ATS vs Synchronization — Cost
Typically:
Basic ATS
Simplest.
AMF Panel
Adds generator control/automatic standby functions.
Synchronization Panel
Most sophisticated because it can require:
- synchronization controllers
- governor interface
- AVR interface
- multiple breakers
- PLC/HMI
- load sharing
- power management
- protection
- communications
But cost should follow function.
Do not purchase synchronization equipment where basic standby transfer is sufficient.
And do not attempt to make a basic AMF system perform multi-DG parallel operation.
We have opened panels where someone had tried exactly that: two AMF controllers, one per DG, with a hand-built interlock scheme and a hope that the breakers would never close out of step. There is no synchro-check element in that arrangement, so nothing prevents an out-of-phase closure, and an out-of-phase closure on a 1000 kVA alternator is a mechanical event, not an electrical trip. Our recommendation: if there is any chance the plant will need two DGs running together within the panel's life, say so at design stage. Providing space, a spare cubicle and cabling provision for a synchronizing controller and a bus-coupler breaker at the outset costs a fraction of retrofitting a paralleling scheme into a finished panel three years later, which usually means replacing the panel.
What Should an RFQ Say?
Avoid:
“Required automatic DG panel.”
Instead specify:
Sources
- Number of utility sources
- Number of DGs
- DG ratings
Required Modes
- AMF?
- ATS?
- DG-DG parallel?
- DG-mains parallel?
- Open transition?
- Closed transition?
DG Functions
- auto start
- dead-bus closing
- synchronization
- kW sharing
- kVAr sharing
- load-dependent start/stop
Plant Functions
- load shedding
- load restoration
- priority rotation
- N+1 reserve
Interface
- PLC
- HMI
- SCADA
- BMS
Applicable Standards
For transfer-switching equipment, the current IEC edition is:
IEC 60947-6-1:2026.
For applicable LV panel assemblies:
IEC 61439-1:2020
and:
IEC 61439-2:2020
define general and PSC assembly requirements respectively.
BIS currently lists Indian adoptions:
IS/IEC 61439 Part 1:2020
and:
IS/IEC 61439 Part 2:2020.
FAT Requirements
AMF FAT
Test:
- mains healthy
- mains fail
- DG start
- DG healthy
- transfer
- mains return
- retransfer
- cooldown
- fail-to-start
ATS FAT
Test:
- Source A healthy
- Source B healthy
- source failure
- preferred-source logic
- electrical/mechanical interlock
- manual/auto modes
Synchronization FAT
Additionally test/simulate:
- voltage mismatch
- frequency mismatch
- phase-angle permissive
- dead-bus closing
- sync failure
- load-share logic
- generator trip
- start/stop sequencing
- load shedding
Actual dynamic tuning with real governors, AVRs and generators may additionally require site commissioning.
How Wisdom Techno Solutions Approaches These Panels
We engineer AMF, ATS and synchronization panels according to the actual operating requirement rather than applying one standard control scheme.
Wisdom Techno Solutions is a licensed partner for three design-verified switchgear platforms: Rittal Ri4Power (Rittal Solutions Partner since 2021 — the Ri4Power system carries Intertek ASTA design verification to IEC 61439-1 and -2 Edition 3, with copper and aluminium busbar systems up to 6300 A), C&S CX (Licensed Partner since 2023, up to Form 4B Type II) and Siemens SIEPAN Elite/8PU (IEC 61439 Solutions Partner since 2024). We build to each system's verified configuration and routine-verify every assembly in-house at our Vadodara, Gujarat facility, for industrial, EPC and infrastructure projects across India. That places the changeover-state busbar loading inside a verified design envelope.
Depending on approved project scope, we engineer panels involving:
- AMF
- automatic source transfer
- DG synchronization
- multiple generator breaker control
- PLC/HMI
- load-sharing interfaces
- load shedding
- SCADA/BMS integration
- interlocks
- metering
- alarms
The most important first question is:
“Are the sources only being transferred—or are they required to operate in parallel?”
That determines the basic architecture.
Conclusion
The easiest way to remember the difference is:
AMF = What happens when mains fails?
ATS = Which source supplies the load?
Synchronization = Can multiple energized sources operate together?
For one standby DG:
AMF/ATS may be enough.
For multiple DGs running together:
Synchronization and load sharing are required.
For automatic capacity management:
Power Management System is required.
Do not specify the panel name first.
Define the operating sequence first.
Then select the control architecture.
Planning an AMF, ATS or DG synchronization panel?
Share the SLD, DG ratings, utility arrangement and complete source operating philosophy with Wisdom Techno Solutions for project-specific panel engineering.
Related Guides
- 3-pole vs 4-pole ATS
- DG synchronization panel
- Load list and transformer/incomer sizing
- 2 incomer + bus coupler interlocking
- Product page: AMF panel
- Product page: DG synchronization panel
Frequently Asked Questions
What is the difference between AMF and ATS?
AMF — Automatic Mains Failure — refers to the complete standby-generator operating function: detect that the mains has failed, start the DG, transfer the load, and reverse the sequence with a cooldown when the mains returns. An ATS is narrower: it is the source-transfer device or system that decides which of two available sources feeds the load, and it may only issue a generator-start contact rather than manage the engine. In practice most single-DG panels combine both, which is why the names are used interchangeably in the market. Neither one parallels two live sources — that requires synchronization.
Can AMF and ATS be in the same panel?
Yes. Many standby-generator panels combine mains-failure detection, generator start and automatic source transfer.
Does an ATS synchronize generators?
No. A normal ATS transfers the load from one source to another and is designed so that only one source feeds the load at a time; it has no synchro-check element, no governor or AVR interface and no load-sharing function. Multi-generator synchronization needs a dedicated paralleling controller that matches phase sequence, voltage, frequency and phase angle before permitting the incoming breaker to close, then balances kW and kVAr afterwards. The one partial exception is closed-transition ATS, which briefly parallels two already-synchronized sources during transfer — but that is a controlled overlap of a few cycles, not continuous parallel operation with load sharing.
When is a DG synchronization panel required?
A DG synchronization panel is required whenever two or more generators, or a generator and another energised source, must intentionally operate in parallel. The usual trigger is capacity: if the load that must be supported during a mains failure exceeds what the largest single DG can carry, the machines have to run together. It is also required for load-dependent start/stop of multiple DGs, for peak shaving alongside the utility, and for any grid-parallel operation. Before committing to it, confirm whether the stated demand is the essential load or the total connected load — splitting essential and non-essential distribution sometimes removes the need for paralleling altogether.
What is load sharing?
Load sharing is the continuous distribution of active power (kW) and reactive power (kVAr) between generators that are already paralleled onto a common bus. It happens after synchronization is complete — synchronization gets the breaker closed, load sharing keeps the machines balanced from then on. kW sharing is controlled through the engine speed governor, while kVAr sharing is controlled through the excitation and AVR, which is why the two are tuned separately. Poor kW sharing shows up as one engine working harder than the other; poor kVAr sharing shows up as circulating current between alternators with the kW balance looking correct.
What is dead-bus closing?
Dead-bus closing allows the first healthy generator to close directly onto a de-energised common bus and energise it, without attempting to synchronize. There is nothing to synchronize to when bus voltage is zero, so the normal phase-angle and frequency permissives cannot be satisfied and must be bypassed under a controlled dead-bus condition. Once that first machine has energised the bus, every subsequent generator must synchronize to the live bus in the normal way before its breaker closes. The critical design point is that only one machine may hold dead-bus closing priority at any moment — if two controllers each decide they are first, both can close onto a dead bus simultaneously and out of phase.
Can a normal AMF panel parallel DG and mains?
Not normally. Intentional mains paralleling requires a suitable synchronization/protection/control architecture.
Which IEC standard applies to ATS?
IEC 60947-6-1:2026 currently covers transfer switching equipment within its scope, including manual, remote and automatic transfer switching equipment, standalone ATS controllers, bypass and isolation TSE, and closed-transition ATSE. Where the transfer equipment is built into a complete LV assembly, the assembly itself is covered by IEC 61439-1:2020 and IEC 61439-2:2020, with the Indian adoptions listed by BIS as IS/IEC 61439 Part 1:2020 and IS/IEC 61439 Part 2:2020. A specification should name both the device standard and the assembly standard. Breaker-based changeover schemes use devices to IEC 60947-2 and are not automatically equivalent to type-tested transfer switching equipment.
What should I provide for quotation?
Provide the SLD, the number and rating of every source, the required transfer modes, whether DG-to-DG or DG-to-mains paralleling is needed, the load-sharing philosophy, the load-shedding and restoration requirement, and the PLC, HMI or SCADA interface expected. The single answer that decides the architecture is whether two sources ever need to be connected together at the same time — everything else follows from that. Also state the essential load separately from the total connected load, and the system earthing and neutral arrangement, since these determine the changeover pole count. "Required automatic DG panel" is not a specification and will produce three suppliers quoting three different scopes.