The A320 Electrical System: A Foundation Series for Oral Exam Preparation
Most A320 pilots can name the electrical sources. Fewer can walk the bus structure without hesitating.
Most A320 pilots can name the electrical sources. Fewer can walk the bus structure without hesitating, and fewer still can state the conditions the manual attaches to the answers, which is usually where an oral exam goes next.
This is the hub for a three-week series on the A320 electrical system, written for pilots preparing for a type rating or recurrent oral. Every claim across the series is anchored to the Flight Crew Operating Manual and has been verified against the manual text rather than summarized from memory or inherited from a study guide.
Start here for the architecture. The weekly pages go deeper into the specific questions examiners actually ask.
The Architecture, in Brief
In normal configuration the A320 electrical power system is constituted of 𝘁𝘄𝗼 𝗲𝗻𝗴𝗶𝗻𝗲 𝗴𝗲𝗻𝗲𝗿𝗮𝘁𝗼𝗿𝘀 and 𝗼𝗻𝗲 𝗔𝗣𝗨 𝗴𝗲𝗻𝗲𝗿𝗮𝘁𝗼𝗿. On the ground, either the APU generator or external power may supply the complete system. If normal AC power is not available, an emergency generator can provide AC power. If all AC power is not available, DC power from the batteries can be inverted into AC power.
That is the manual's own opening description, and it is worth learning in that shape because it moves from normal to degraded in the same order the system does.
Frequently Asked Questions
What are the main AC and DC buses on the A320?
On the AC side, 𝗔𝗖 𝗕𝗨𝗦 𝟭 is normally supplied by GEN 1 through generator line contactor 1, and 𝗔𝗖 𝗕𝗨𝗦 𝟮 is normally supplied by GEN 2 through generator line contactor 2. The 𝗔𝗖 𝗘𝗦𝗦 𝗕𝗨𝗦 is normally supplied by AC BUS 1.
On the DC side, 𝗧𝗥 𝟭 normally supplies DC BUS 1, the DC BAT BUS, and the DC ESS BUS. 𝗧𝗥 𝟮 normally supplies DC BUS 2.
𝗛𝗢𝗧 𝗕𝗨𝗦 𝟭 and 𝗛𝗢𝗧 𝗕𝗨𝗦 𝟮 are permanently connected to BAT 1 and BAT 2 respectively.
A useful way to hold it: GEN 1 to AC BUS 1 to AC ESS BUS, and through TR 1 to DC BUS 1 plus DC BAT BUS plus DC ESS BUS. GEN 2 to AC BUS 2, and through TR 2 to DC BUS 2.
How many transformer rectifiers does the A320 have?
There are 𝘁𝘄𝗼 𝗺𝗮𝗶𝗻 𝘁𝗿𝗮𝗻𝘀𝗳𝗼𝗿𝗺𝗲𝗿 𝗿𝗲𝗰𝘁𝗶𝗳𝗶𝗲𝗿𝘀, TR 1 and TR 2, which supply the aircraft electrical system with up to 200 A of DC current. A third identical transformer rectifier, the 𝗘𝗦𝗦 𝗧𝗥, can power the essential DC circuit from the emergency generator if the engine and APU generators all fail, or if TR 1 or TR 2 fails. Where fitted, the FCOM also lists a fourth transformer rectifier, 𝗧𝗥 𝗘𝗻𝘁𝗲𝗿𝘁𝗮𝗶𝗻𝗺𝗲𝗻𝘁, which powers the DC Entertainment busbar for the IFE system.
Answering only TR 1 and TR 2 is 𝗶𝗻𝗰𝗼𝗺𝗽𝗹𝗲𝘁𝗲.
Answer: TR 1 and TR 2 are the two main TRs; ESS TR is the essential TR; and where fitted, TR Entertainment powers the DC Entertainment busbar.
𝗗𝗼 𝗻𝗼𝘁 give "three TRs" as a universal aircraft-total answer. The correct total depends on whether TR Entertainment is fitted.
Is the A320 DC distribution symmetric?
In normal configuration it is 𝗻𝗼𝘁. TR 1 normally supplies three buses, DC BUS 1 and the DC BAT BUS and the DC ESS BUS, while TR 2 normally supplies DC BUS 2 only.
The recovery, however, is 𝘀𝘆𝗺𝗺𝗲𝘁𝗿𝗶𝗰. In a single transformer rectifier failure the other TR automatically replaces the faulty one, and the ESS TR supplies the DC ESS BUS. That holds for a TR 1 fault and for a TR 2 fault alike.
Normal - Asymmetric
- TR 1 supplies: DC BUS 1, DC BAT BUS, DC ESS BUS
- TR 2 supplies: DC BUS 2 only
Recovery - Symmetric
- Single TR failure: the other TR automatically replaces the faulty one
- ESS TR supplies the DC ESS BUS
- Holds for TR 1 fault and TR 2 fault alike
So the normal picture is lopsided and the failure picture is balanced. A candidate who has learned only the normal allocation tends to assume the consequences of losing TR 1 and TR 2 are proportionally different. They are not, because the reconfiguration is generic.
When are the A320 batteries connected to the DC BAT BUS?
The batteries are connected to the DC BAT BUS in the following 𝘁𝗵𝗿𝗲𝗲 𝗽𝘂𝗯𝗹𝗶𝘀𝗵𝗲𝗱 𝗰𝗮𝘀𝗲𝘀.
The manual also publishes a note on the resulting state: 𝗶𝗻 𝗻𝗼𝗿𝗺𝗮𝗹 𝗰𝗼𝗻𝗳𝗶𝗴𝘂𝗿𝗮𝘁𝗶𝗼𝗻 𝘁𝗵𝗲 𝗯𝗮𝘁𝘁𝗲𝗿𝗶𝗲𝘀 𝗮𝗿𝗲 𝗱𝗶𝘀𝗰𝗼𝗻𝗻𝗲𝗰𝘁𝗲𝗱 𝗺𝗼𝘀𝘁 𝗼𝗳 𝘁𝗵𝗲 𝘁𝗶𝗺𝗲.
Those two statements are complementary rather than contradictory, and they sit in different sections. The charging rule describes 𝘄𝗵𝗲𝗻 the batteries connect. The note describes 𝘄𝗵𝗮𝘁 that rule produces across a normal flight, which is a battery that spends most of its time disconnected from the DC BAT BUS. A candidate who can state both, and explain that the second follows from the first, has the complete picture.
Most study material gives only a loose version of the charging case, which is why the published thresholds are worth carrying. "Need charging" and "APU start" are shorthand, not conditions.
Separately from all three cases, 𝗛𝗢𝗧 𝗕𝗨𝗦 𝟭 and 𝗛𝗢𝗧 𝗕𝗨𝗦 𝟮 remain permanently connected to BAT 1 and BAT 2 whether or not the battery line contactor is closed. The battery line contactor connects the batteries to the DC BAT BUS. It is not the path to the hot buses; that is a separate and permanent connection.
The DC BAT BUS itself is normally supplied by TR 1.
What does the BUS TIE do on the A320, and when do the contactors close?
𝗕𝘂𝘀 𝘁𝗶𝗲 𝗰𝗼𝗻𝘁𝗮𝗰𝘁𝗼𝗿 𝟭 and 𝗯𝘂𝘀 𝘁𝗶𝗲 𝗰𝗼𝗻𝘁𝗮𝗰𝘁𝗼𝗿 𝟮 link AC BUS 1 and AC BUS 2 through a centralized tie bus. In BUS TIE AUTO, they automatically open or close to maintain power supply to AC BUS 1 and AC BUS 2.
Both Contactors CLOSED
- Single-engine operation
- Operation on the APU generator
- External power supply
Single source feeding both AC buses through the tie bus
One Contactor CLOSED
- One engine generator supplies its associated AC BUS
- APU generator or external power supplies the other side
Split-source configuration rather than single-source
Both Contactors OPEN
- BUS TIE OFF selected
- Normal two-engine operation with both GENs
A common incomplete answer is that the bus tie closes only if a generator fails. That misses the normal reconfiguration cases the manual explicitly describes, where a single source is supplying the aircraft on the ground or in single-engine operation.
What is the static inverter on the A320 and when does it operate?
The 𝘀𝘁𝗮𝘁𝗶𝗰 𝗶𝗻𝘃𝗲𝗿𝘁𝗲𝗿 transforms DC power from Battery 1 into one kVA of single-phase 115 V 400 Hz AC power, supplied to part of the AC essential bus.
It activates only when the batteries are the sole supplier of electrical power to the aircraft, subject to aircraft speed and battery pushbutton conditions.
It is part of the 𝗰𝗼𝗺𝗽𝗹𝗲𝘁𝗲 𝗲𝗹𝗲𝗰𝘁𝗿𝗶𝗰𝗮𝗹 𝗽𝗼𝘄𝗲𝗿 𝗮𝗿𝗰𝗵𝗶𝘁𝗲𝗰𝘁𝘂𝗿𝗲 but it is not part of the 𝗻𝗼𝗿𝗺𝗮𝗹 𝗰𝗼𝗻𝗳𝗶𝗴𝘂𝗿𝗮𝘁𝗶𝗼𝗻 source list. Candidates who include it among the normal sources, or who exclude it from the complete architecture, are making the same mistake from opposite directions.
What are the A320 electrical power ratings?
Each engine generator is driven by an 𝗜𝗻𝘁𝗲𝗴𝗿𝗮𝘁𝗲𝗱 𝗗𝗿𝗶𝘃𝗲 𝗚𝗲𝗻𝗲𝗿𝗮𝘁𝗼𝗿 and produces 115/200 V three-phase AC at a constant 400 Hz, rated up to 90 kVA. The APU generator produces identical output ratings and can replace either or both engine generators.
The generators are 𝗻𝗲𝘃𝗲𝗿 𝗰𝗼𝗻𝗻𝗲𝗰𝘁𝗲𝗱 𝗶𝗻 𝗽𝗮𝗿𝗮𝗹𝗹𝗲𝗹.
The two main transformer rectifiers supply the aircraft electrical system with up to 200 A of DC current. The static inverter produces one kVA. The two main batteries each have a normal capacity of 23 Ah.
Where the Weekly Pages Go
Spoke 1: Source Priority and the External Power Indications
Which source powers the aircraft when engine generators, external power, and the APU generator are all available. What the AVAIL light means before you press the pushbutton and what the blue ON light does and does not tell you afterwards. What actually happens to the APU generator while external power is feeding the network.
Read Spoke 1 → · Companion article on LinkedInSpoke 2: Single Source Loss and Automatic Reconfiguration
What triggers a generator fault, whether the reset attempt has a published limit, and why the guarded IDG pushbutton is the wrong reach for a generator fault. The published constraints on the IDG disconnect, the oil temperature ladder, and what the aircraft reconfigures on its own before the crew touches anything.
Read Spoke 2 → · Companion article on LinkedInSpoke 3: Emergency Electrical Configuration
Loss of all main generation. The emergency generator, the Ram Air Turbine, and battery-only operation. What is shed, at what speeds, and what remains. In preparation.
Why the Conditions Matter More Than the Facts
A pattern runs through this whole chapter. The manual attaches conditions to most of its statements, and the common failure on an oral is not forgetting the fact. It is giving a universal answer to a conditional question.
The APU generator replaces a failed engine generator 𝗶𝗳 𝗶𝘁 𝗶𝘀 𝗮𝘃𝗮𝗶𝗹𝗮𝗯𝗹𝗲. Galley shedding differs between flight and ground and between aircraft standards. Essential bus recovery after an AC BUS 1 fault is automatic on aircraft with one modification and a crew action on aircraft without it. Crew awareness sometimes means monitor and continue and sometimes follows a directed selection.
Learning the conditions is what separates a candidate who has read the manual from one who has read a summary of it.
