BAS-301 Visual Aid Library
Figure-use rule
Each figure is an orientation and reasoning aid, not a project drawing. Learners must pair it with the current sequence, point list, wiring/piping documents, manufacturer instructions, and as-found evidence.
Normal-rule anchor
Low voltage is not automatically low risk, and online training does not authorize energized testing.
Case overlay
A learner proposes to check resistance across an energized 24 Vac relay coil.
Calculation/evidence callout: Compare expected potential between exact test points and verify instrument range/category before measurement.
Normal-rule anchor
Nominal 24 Vac at the transformer does not prove adequate voltage at the energized device under load.
Case overlay
Several actuators start together and the controller reboots while open-circuit voltage appears normal.
Calculation/evidence callout: VA = volts×amps; percent loading = connected VA/rated VA×100; voltage-drop percent = drop/source×100.
Normal-rule anchor
A blown fuse or tripped safety is evidence of a condition, not permission to install a larger device or repeatedly reset.
Case overlay
A secondary fuse opens whenever a damper actuator is commanded near end of travel.
Calculation/evidence callout: Compare measured/supplied current to device, conductor, and protective ratings without changing specified protection.
Normal-rule anchor
A RIB commands the starter or VFD control input; it never switches one leg of a three-phase motor circuit.
Case overlay
A technician proposes to place a RIB relay in phase B because the BAS output cannot carry motor current.
Calculation/evidence callout: Calculate coil VA/current and compare contact voltage/current/load type to the exact relay rating.
Normal-rule anchor
A bypass may make equipment run while destroying the protection and evidence needed to diagnose the real condition.
Case overlay
The fan will run in HAND but not AUTO, and one safety contact is open.
Calculation/evidence callout: Use source-to-load potential measurements across defined nodes to locate the voltage transition under an approved procedure.
Normal-rule anchor
Signal compatibility requires range, action, reference, power, fail state, and authority—not just matching terminal labels.
Case overlay
A DDC AO drives an EP transducer correctly, but the pneumatic actuator does not stroke.
Calculation/evidence callout: Convert 0–10 V or 4–20 mA command to percent and expected 3–15 psi branch pressure using supplied linear ranges.
Normal-rule anchor
Opening or switching one phase of a running three-phase motor is not a BAS control strategy and can damage equipment.
Case overlay
A three-phase motor hums, current proof is present, and one phase is lost upstream.
Calculation/evidence callout: Use supplied phase currents to calculate percent current imbalance by the specified method and escalate unacceptable results.
Normal-rule anchor
An overload trip protects the motor circuit; repeated reset without cause review is not troubleshooting.
Case overlay
The starter coil is energized, the contactor pulls in, and the motor does not turn.
Calculation/evidence callout: Compare supplied full-load current, service factor/application data, and approved overload setting; do not invent settings.
Normal-rule anchor
A VFD output-frequency display is not proof of motor rotation, belt condition, airflow, or correct parameterization.
Case overlay
The BAS commands 60%, but the drive remains at 30 Hz because the keypad is the active reference source.
Calculation/evidence callout: Convert command percent to expected reference and frequency only from the approved min/max mapping and current source.
Normal-rule anchor
The completed diagnosis identifies mechanism, responsible role, affected protection, and zero unaccounted temporary states.
Case overlay
A fan is restored after a relay change, but the VFD remains in LOCAL and the panel cover is open.
Calculation/evidence callout: Reconcile every test point, temporary state, mode, cover, fault, alarm, and affected-mode retest before closure.