Electrical System

Question 1

Describe the Electrical system on the Cessna 172.

Answer 1

**E.A.B.S.”” – Electricity Always Brings Support.

E for Electricity: Supplied by a 14-volt DC system.

A for Alternator: Engine-driven alternator

B for Battery (12 - volt): Located on the left forward portion of the firewall.

S for Split Bus Bar: Powers all circuits.

Question 2

What happens if the circuit breaker pops?

Answer 2

If the circuit breaker has tripped (“popped’), the pilot can push in the alternator field circuit breaker to reset the alternator. This might allow normal electrical function to be restored. Also, the pilot can try turning the alternator off and on again by cycling the ALT side of the Master Switch (“cycling the switch”).

Question 3

Describe the Master Switch on the Cessna 172.

Answer 3

The Master Switch is a split rocker type switch. The right half is labeled BAT and the left half is labeled ALT. With the BAT side on and the ALT side off, the alternator is removed from the system and the entire load is on the battery.

Question 4

How many “busses” do we have?

Answer 4

3

Question 5

What are the bus names?

Answer 5

1. ALT BUS
2. Electronic Bus
3. Primary Bus

Question 6

What is an ammeter?

Answer 6

The ammeter indicates the flow of current, in amperes, from the alternator to the battery or from the battery to the aircraft electrical
system.