This simulator models a three-appliance radial Notification Appliance Circuit (NAC) — horns and strobes wired in parallel off a two-conductor loop — with distributed conductor resistance, remote end-of-line supervision and fault injection. Enable alarm output, adjust source voltage and wiring, and watch how downstream voltage, current and appliance operation respond.
• Equipment laboratory tab: a real-time 3D cutaway workbench of the NAC power supply/protection, the two-conductor radial circuit, three horn/strobe appliances and the end-of-line resistor, with Home view, Focus selected part, Show full enclosure / Exploded view toggle, Auto rotate, Expand and Hide/show labels camera controls, a clickable numbered component list with callouts, a live stats readout, a 'What is happening?' sequence narrative, switch-state tokens and a per-appliance readings table, plus an experiment control desk with Pause/Advance 0.1 s/Advance 1 s stepping, a playback-speed selector (real time, 10× slow motion, 10× faster, 1 minute per second), Start trial/Stop equipment/Silence audible outputs actions, and controls for Enable alarm output, alarm source voltage (18-28 V DC), appliance rated current at 24 V (0.05-0.5 A), loop resistance per segment (0.1-6 Ω), circuit fault (healthy / open segment / short circuit), which appliance the open occurs before, and whether the end-of-line resistor is present. • Curves & measurements tab: a primary-measurements chart (first vs. last appliance voltage), a response/sequence chart (alarm current vs. standby supervision current), the model equations, and snapshot measurement readouts. • Experiments tab: guided experiments (standby supervision, alarm power, excessive conductor loss, final-segment-open) each with an expected outcome, a Run model checks button that runs the built-in verification suite against independent fresh models, and a timestamped event log with a Prepare trial report export. • Learn & assess tab: lesson content on supervising the wiring, silencing vs. continuity, a knowledge-check quiz with reset, and a scope/references note linking to an external NAC installation guide.
A Notification Appliance Circuit powers the horns and strobes that alert building occupants during an alarm. In this model, the NAC panel/protection block feeds a two-conductor radial loop; each appliance taps the alarm-positive and return buses in parallel, and every wire segment between taps adds loop resistance. Downstream current determines each segment's voltage drop, so voltage sags at appliances further from the source — which is why raising the loop resistance per segment or the appliance current draw can push the last appliance below its 16 V operating threshold in the model.
In standby, a small sensing current flows out to a remote end-of-line resistor and back, which supervises the complete outgoing and return path — an EOL resistor at the panel instead of the far end would leave the downstream wiring outside the supervised loop. When alarm output is enabled, all connected appliances draw their modeled resistive load current; an open segment removes every appliance downstream of the break, while a short circuit disables the source output entirely.
Rappliance is derived from 24 V divided by the appliance's rated current, and each segment's voltage drop equals the downstream current times that segment's resistance — so the live per-appliance voltage table shows the same cumulative-loss idea the model equations describe. Standby sense current follows Isense = 5 V ÷ (10 kΩ + 4.7 kΩ + cable resistance), which is why a small nonzero supervision current appears at rest with appliances off.
The Run model checks button exercises independent, freshly-built models — separate from your current trial — to confirm invariants such as correct segment-drop accumulation and fault behavior hold generally, not just for the settings you happen to have selected. Audible silence and visual (strobe) output are tracked separately in the sequence narrative: silencing horns does not disable strobes, and acknowledging an alarm never substitutes for restoring the initiating condition. All appliance parameters are equivalent resistive loads and a generic 16 V pass/fail threshold — not a specific listed device's manufacturer current, voltage or synchronization specification.
It models a three-appliance radial Notification Appliance Circuit with equivalent resistive horn/strobe loads, distributed two-conductor loop resistance, remote end-of-line supervision, and open-segment or short-circuit fault injection. It is a representative educational sequence, not a listed-device specification, wiring design or commissioning procedure.
Placing supervision at the remote end verifies the complete outgoing and return path. A resistor at the source would only confirm the panel terminals are wired, leaving all of the downstream wiring and appliance connections unsupervised.
An open segment removes alarm power from every appliance downstream of the break point you select (appliance 1, 2 or 3), while the modeled first two appliances stay powered if the open is placed after them. A short circuit disables the source output entirely, per the built-in protection behavior.
The Run model checks button runs the shared checks.js verification suite against independent, freshly built models — separate from your live trial — confirming invariants like voltage-drop accumulation and fault-response behavior hold consistently in the underlying circuit model.