NITA Auto Electrician Trade Test flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

Voltage equals current multiplied by resistance (V = I × R). Rearranged, I = V/R and R = V/I. It applies to any resistive circuit element at constant temperature.

Power formula

Electrical power equals voltage times current (P = VI). Substituting Ohm's law gives P = I²R and P = V²/R, used to size fuses and cable.

Parallel resistance rule

Reciprocals of branch resistances add to give the reciprocal of total resistance. Two resistors simplify to R1 × R2 divided by R1 + R2.

Voltage drop calculation

For a feed-and-return cable run, Vd = 2 × resistivity × length × current divided by cross-section area. Copper resistivity is about 0.0175 ohm square millimetre per metre.

Battery state of charge

Rested open-circuit voltage indicates charge: about 12.7 V is full, 12.4 V is 75 percent, 12.2 V is 50 percent and 12.0 V is 25 percent at 25 degrees Celsius.

Cold cranking amps

Current a 12 V battery delivers at minus 18 degrees Celsius for 30 seconds while terminal voltage stays at or above 7.2 V. It indicates starting capability in cold weather.

Electrolyte specific gravity

Fully charged lead-acid electrolyte reads about 1.265, half charge about 1.200 and discharged about 1.120. Correct the reading by 0.004 per 10 degrees from 25 Celsius.

Battery load test

Apply half the rated cold cranking current for 15 seconds. A healthy battery holds above 9.6 V at 20 degrees Celsius, adjusted down about 0.02 V per degree colder.

Alternator ripple test

Measure AC volts at the battery with the engine running. Ripple above roughly 0.5 V AC indicates a failed rectifier diode or a stator fault.

Charging voltage specification

Regulated alternator output is typically 13.8 to 14.5 V at 25 degrees Celsius. Lower means undercharging; above about 15 V risks overcharging and battery damage.

Cranking voltage drop test

While cranking, measure from battery positive to starter terminal and battery negative to engine block. Each reading should stay below about 0.5 V.

Starter solenoid windings

The solenoid has pull-in and hold-in windings. A single click with no cranking often means the hold-in winding or its earth is open.

Headlamp dip aim

Dipped beam should fall about 1 percent below horizontal, roughly a 10 cm drop over 10 m. This illuminates the road without dazzling oncoming drivers.

Indicator rapid flash cause

A flasher unit times the lamps by load. When one indicator lamp fails, current drops and the remaining lamps flash rapidly, signalling the fault.

Halogen bulb handling

Never touch the glass with bare fingers. Skin oils create hot spots that crack or shorten the bulb. Hold by the base or use clean gloves.

Ignition dwell angle

Crank degrees during which the primary circuit stays closed and coil current builds. Too little weakens the spark; too much overheats the coil.

Wasted spark ignition

One coil fires two cylinders at once, one on compression and one on exhaust. A misfire on both paired cylinders points to a shared coil or driver.

Knock sensor function

Detects cylinder block vibration from detonation and signals the control unit, which retards ignition timing. A failed sensor usually causes reduced power and poorer economy.

Fuse selection rule

The fuse rating must exceed normal circuit current but must not exceed the cable's current capacity. Never fit a larger fuse to stop repeated blowing.

DIN terminal 30 and 15

Terminal 30 is permanent battery positive, live with the ignition off. Terminal 15 is ignition-switched positive. Terminal 31 is earth return.

Four-pin relay terminals

Terminal 30 is supply, 87 is output to the load, 86 is coil feed and 85 is coil earth. Terminal 87a is the normally closed contact.

Ammeter connection rule

An ammeter is connected in series with the circuit because it has very low resistance. Connecting it across a battery causes a short and blows its fuse.

Parasitic drain limit

With all loads off and modules asleep, current draw should typically stay below 30 to 50 milliamps. Higher draw is traced by clamping each fuse circuit.

Continuity test limitation

A continuity test proves a path exists but not that it carries current. A single remaining wire strand reads near zero ohms yet fails under load.

NTC temperature sensor

Resistance falls as temperature rises. Typical values are about 2.5 kilohms at 20 degrees Celsius and 300 ohms at 90 degrees, read as a voltage divider.

Hall-effect sensor output

Requires a supply and produces a square-wave digital signal as the target passes. Used for crank, cam and wheel speed sensing where a clean pulse is needed.

Oxygen sensor voltage range

A narrow-band sensor switches between about 0.1 V lean and 0.9 V rich. A lazy or fixed reading indicates a failed sensor or an air-fuel fault upstream.

Pulse-width modulation

Switching a supply on and off rapidly controls average voltage. Average voltage equals duty cycle times supply, so 50 percent duty on 12 V gives about 6 V.

Locked-rotor current

A stalled motor draws several times its rated current because back-EMF disappears. It overheats quickly and can damage wiring or blow the protection fuse.

Motor suppression capacitor

Fitted across motor or inductive load terminals to absorb voltage spikes when the circuit opens. It protects switches, relays and sensitive control units from arcing damage.

High-voltage cable identification

Orange cable marks high-voltage circuits on hybrid and electric vehicles. Only trained personnel using rated gloves, tools and meters may work on them.

Cable size calculation

Cross-section area equals 2 times resistivity times length times current, divided by permitted voltage drop. Choose the next standard metric size above the result.