voltage lab
Switch OPEN · Load OFF
Choose a condition, then move the meter probes to find the voltage drops.
Use the Power ON/OFF button at the far left to energize or de-energize the transformer. The separate Close/Open switch button controls the load circuit. Select the red and dark-gray circles beside each test terminal. The probes move to the selected points. You can put both probes on the same terminal.
Test point locations
A — Transformer hot F — Transformer common
B — Before switch C — After switch
D — Before motor E — After motor
● Red probe ● Dark-gray probe
DIGITAL VOLTMETER
24 V
● Red probe: A ● Black probe: F
Power OFF represents removing the transformer primary supply; every A–F test point is at 0 V in this simplified model. Simplified educational AC model: 24 VAC rated source (18 VAC in the defective-transformer fault, independent of switch position), motor operating impedance modeled as a purely resistive 48 Ω load, and corroded switch as 12 Ω series resistance. In real motors, operating AC impedance and power-off DC winding resistance differ; the displayed 48 Ω DC winding value is illustrative and is not used to calculate current. Component ohm labels represent isolated, power-off checks, not energized readings. The defective-transformer setting models a steady 18 VAC output with 120 VAC supplied to the primary; this is a simplified fault scenario, not a specific diagnosis from winding resistance. An open winding has no current; if both switch and motor are open, the downstream conductor floats, so its voltage cannot be assigned reliably. High-impedance meter; AC magnitudes shown. Never measure resistance on energized equipment.