In short. A generator installation has at least three kinds of wiring diagram: the manufacturer’s set and controller drawings, the panel builder’s AMF or ATS drawings, and the project as-built that shows how everything was connected on site. They are different records and only the as-built, kept current after every modification, describes the system a technician is actually touching. Confirm the drawing revision matches the installed controller, panel and connections before using it for fault-finding or modification.
Three drawings, three different truths
When a set fails to transfer load at two in the morning, the technician reaches for whatever drawing is in the panel pocket. Whether that drawing helps or misleads depends on which of three records it is.
| Drawing | Issued by | Shows | Limitation |
|---|---|---|---|
| Manufacturer or OEM drawing | Engine, alternator, controller or set builder | Internal wiring of the set, controller terminals, standard AVR and sensor connections | Generic to the model; does not show site panels or field cabling |
| Panel builder drawing | AMF, ATS or synchronising panel manufacturer | Control logic, contactor or breaker wiring, mains and generator sensing, interlocks | Shows the panel as designed and shipped, not as connected on site |
| Project as-built | Installing contractor or consultant | Field cables, terminal numbers, interconnections between set, panel, distribution board and remote signals | Only correct until the first undocumented change |
All three are needed. The OEM drawing explains what the controller expects on each terminal, the panel drawing explains what the panel does with those signals, and the as-built explains which physical cable carries them. A diagnosis that uses only one of the three will often be wrong at the interface between them, which is exactly where most transfer and auto-start faults live.
The circuits a generator drawing set should cover
DC starting and control circuit
Battery, isolator, starter solenoid, charging alternator, battery charger, fuel solenoid or actuator, and the controller’s DC supply. Most no-start calls are resolved in this circuit, and most of them are wiring or battery problems rather than engine problems.
Engine sensing
Oil pressure, coolant temperature, speed pickup or alternator frequency sensing, fuel level and any emission system signals on a CPCB IV+ set. A repeated low oil pressure alarm can be a real pressure fault, a failed sender, a chafed wire or a bad earth, and the drawing tells you where to measure to separate them.
Alternator and AVR
Main stator output, sensing to the AVR, excitation supply from the exciter or PMG, and the droop CT where sets are paralleled. The AVR connection diagram belongs with the alternator manual and must match the AVR actually fitted.
Mains and generator sensing, transfer and interlocks
Three-phase mains sensing at 415 V, generator voltage and frequency sensing, the start signal from the AMF logic to the controller, contactor or breaker close and trip coils, auxiliary contacts, and the mechanical and electrical interlocks that prevent both sources closing together. The AMF panel and automatic transfer switch guides explain the sequence these circuits implement.
Protection, metering and remote signals
Current transformers, protection relay inputs and trips, metering, earth fault sensing, remote start, emergency stop, common alarm and any BMS or SCADA connections. Remote signals are the circuits most often added after commissioning and least often drawn.
Modification control: keeping the drawing and the panel the same system
A drawing is only useful while the drawing and the physical panel still describe the same thing. Sites drift. A contactor is replaced with a different auxiliary contact arrangement, a remote start is added for a new BMS, a timer is bypassed to cure a nuisance trip, a controller is replaced after a lightning strike. Each change that is not recorded converts the as-built into a historical document, and the next technician will spend the first hour of a breakdown discovering that.
- Every authorised change should be marked in red on the master drawing in the panel, with the date and the name of the person who made it.
- Marked-up drawings should be formally reissued at a sensible interval, with a new revision number, and the superseded copy removed from the panel pocket.
- A change that alters the transfer sequence or an interlock should be retested as a sequence, not just checked for continuity.
- Photographs of the panel interior and terminal strips, taken at commissioning and after each change, are cheap insurance.
Using a drawing safely for fault-finding
Verify the drawing identity first: the panel builder’s job number or the project drawing number, the revision, and the controller model shown on the drawing against the one installed. Then verify a few known points against reality before trusting the rest, for example the terminal numbers of the start signal and the mains sensing. If the first two checks disagree with the drawing, stop treating it as current.
Control panels carry 415 V on the sensing and power circuits and the generator can start automatically when mains sensing is disturbed. Isolate and lock out the set and the mains supply, or put the controller in a safe manual or off mode, before working inside the panel, and treat any drawing-based assumption about a dead terminal as unproven until measured. The controller diagnostics and ATS service pages describe how we approach these faults with the drawing and the meter together.
Drawings for new installations and coordination
For a new installation the wiring diagram sits alongside the single-line diagram, the cable schedule and the general arrangement. The single-line diagram defines sources, breakers and ratings; the wiring diagram defines control; the cable schedule defines sizes and routes; the GA, BIM and CAD resources define physical fit. The commissioning record should reference the revision of each, so that the drawing set handed over is the one that was tested. Controller settings, relay settings and the alarm matrix belong in the same handover package.
Common mistakes
- Fault-finding from the OEM drawing alone when the fault is in the field cabling, which wastes hours testing a controller that is behaving correctly.
- Bypassing a timer or interlock to clear a nuisance trip without recording it, which removes a protection the next person does not know is missing.
- Replacing a controller with a different model and reusing the old drawing, so terminal references and alarm logic no longer match.
- Assuming a terminal is dead because the drawing shows no supply, which exposes the technician to 415 V from an undrawn connection.
- Handing over a project with the panel builder’s standard drawing instead of a true as-built, which leaves the remote signals and site interconnections undocumented.
What to send us
Send the panel builder’s label and job number, the set and controller model, the drawing number and revision of anything you already hold, and clear photographs of the panel interior and terminal strips. Describe the circuit you are investigating, whether it is starting, sensing, transfer, protection or a remote signal, and the symptom, for example starts in manual but not in auto, or transfers but does not retransfer. Send a service enquiry and we will confirm which drawing applies or arrange a site visit. The technical library explains how drawings relate to the other document types.
Questions engineers ask
Can you supply the wiring diagram for my AMF panel?
If the panel was built or supplied by us, yes, against the job number on the panel label. If it was built by another panel builder we will help you identify the builder from the label and controller type, and we can prepare a marked-up as-built from a site survey where the original cannot be traced.
Why does the generator start in manual but not in automatic mode?
The engine and controller are working, so the fault is in the auto start path: the mains sensing, the AMF start signal, the controller’s remote start input, the mode selection or the wiring between them. The panel drawing and the as-built show where to measure along that path.
Is a single-line diagram the same as a wiring diagram?
No. A single-line diagram shows sources, breakers, transformers and loads with one line per circuit and no control detail. A wiring diagram shows every conductor and terminal in the control and power circuits. You need both for an installation and the single-line diagram alone will not find a control fault.
How should we record a change made during an emergency repair?
Mark the master drawing in the panel immediately, with date and initials, and photograph the changed terminals. Report it to whoever owns the drawing set so the change can be reviewed and the drawing formally reissued, and retest the affected sequence once the emergency is over.
Do I need the drawing to add a remote start or BMS signal?
Yes. The controller manual tells you which input accepts a remote start and whether it is volt-free or powered, and the panel drawing tells you whether that input is already used by the AMF logic. Adding the signal without both can disable the automatic sequence or cause unintended starts.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.