BAS-103 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
Voltage exists between two reference points, current requires a complete path, and low voltage is not automatically low risk.
Case overlay
A 24 Vac device has voltage at one terminal to ground but no complete return path and will not operate.
Calculation/evidence callout: Apply Ohm law, P=VI, VA relationships, series/parallel basics, and reasonableness with units.
Normal-rule anchor
Similar voltage readings do not make conductors interchangeable; design, source, listing, protection, and reference path govern.
Case overlay
Two transformer commons are tied without approved design, causing unstable readings and unexpected current paths.
Calculation/evidence callout: Calculate transformer load/current/spare, voltage drop from supplied data, and parallel-load totals; identify assumptions and limits.
Normal-rule anchor
The database label AI/AO/BI/BO does not prove the field signal, wiring, reference, or physical process.
Case overlay
A 4-20 mA sensor is landed as 0-10 V and displays a plausible but wrong value.
Calculation/evidence callout: Calculate linear scaling, loop current/resistor voltage from supplied values, binary truth, and expected normal/fault readings.
Normal-rule anchor
A relay coil and its contacts are isolated functions; normal contact state is defined with the coil de-energized, and ratings/application govern use.
Case overlay
A technician lands a fan-start circuit on NC instead of NO and uses a contact rated for the wrong load type.
Calculation/evidence callout: Build contact truth tables, calculate coil current/VA, compare supplied contact ratings, and reconcile commanded versus actual states.
Normal-rule anchor
Control-circuit logic and safety contacts must be traced in their actual normal/fault states; bypassing is not a training shortcut.
Case overlay
A fan will not start because one series permissive is open, but the BAS output and relay both operate.
Calculation/evidence callout: Apply Boolean/series-parallel reasoning, voltage-drop expectations across open/closed elements, and transition coverage.
Normal-rule anchor
Voltage system and motor nameplate/project documentation govern; BAS normally interfaces with the control circuit, not motor conductors.
Case overlay
A single-phase exhaust fan has control voltage and closed contactor contacts but no motor current because an upstream disconnect is open.
Calculation/evidence callout: Calculate single-phase current/power from supplied values, transformer/control load, expected state readings, and proof timeout.
Normal-rule anchor
All motor-power legs are switched and protected as an approved assembly; a BAS relay belongs in the starter control circuit, never inserted into one power leg.
Case overlay
A RIB relay is installed on one leg of a three-phase motor starter, creating a single-phasing and equipment-damage hazard.
Calculation/evidence callout: Calculate balanced three-phase power from supplied V/I/power factor, current imbalance, control-circuit current, and expected auxiliary-contact states.
Normal-rule anchor
A VFD is power electronics, not merely a relay; BAS control never replaces disconnect, drive safeties, motor protection, or qualified commissioning.
Case overlay
The BAS commands 60 percent, the VFD reports run at 36 Hz, but fan proof and duct pressure remain low.
Calculation/evidence callout: Calculate frequency/speed percentage, fan-law awareness from supplied cases, command/feedback error, ramp/proof timing, and load reasonableness.
Normal-rule anchor
A meter does not make a task safe; qualified-person status, risk assessment, correct instrument, verified condition, method, and PPE/program controls govern.
Case overlay
A continuity beep across a coil is treated as proof that the whole control circuit will work under power.
Calculation/evidence callout: Predict readings from the schematic, apply Ohm law, compare measured/supplied tolerance, and state what each result cannot prove.
Normal-rule anchor
The learner must stop at the authorization boundary even when the likely answer is known; evidence and safe escalation are part of competence.
Case overlay
A motor is off with BAS command on, relay energized, starter coil de-energized, and overload auxiliary open after reset history.
Calculation/evidence callout: Calculate evidence coverage, voltage distribution from supplied readings, imbalance, timing, and temporary-state/record reconciliation.