⠿⠿ CONTROLS — drag to move ⠿⠿
RH1 Speed: Slow Fast 0 Ω 🔊 80% Meter:
resize ⤡
STATUS Ready — click switches to toggle
▾ LEGEND
Terminal numbers: 6
Wire numbers = brackets: [6]
Component / Pin # = parentheses: (1)
Field components marked with *
● Green = voltage present
System 1 — Power Flow Simulator (v0.9.4.17) SUPPLY +24VDC DISC LOTO Comm 1 [2] 11 F1 [3] 12 [4] 13 CB2 [5] 14 15 SW3 16 [6] 39 W PL13 INCAND 40 [7] 6 [6] 23 SW6 AUTO OFF MAN [8] 24 LS1* LVL SW 57 45 G PL16 INCAND 46 [7] 8 [11] 18 [10] 22 17 SW4 47 M17 M17 BLDC Motor 48 33 PB10 (Stop) [12] 31 34 PB9 (Start) [13] 32 (6) CR1-1a (4) [13] CR1(8) CR1 coil LED — green when energized CR1 YJ2N-LY DC24 CR1(7) [7] 9 43 Y PL15 INCAND 44 (5) CR1-2a (3) [14] 37 CW CCW (Direction) SW12 38 [15] CR2(2) CR2 coil LED — green when energized CR2 750R-2C-24V Push to Test — toggles CR2 armature manually (click to press, click to release) PTT CR2(7) [7] 10 Speed Control Rheostat* (3) [16] (5) CR2-1a CR2-2b (1) [17] 49 Red PMDC Motor M18 50 Blk [18] (8) M18 DIRECTION Red+ / Blk− = CW Blk+ / Red− = CCW CR2-1b (4) CR2-2a (6) [7] [7] LEGEND: Terminal numbers: 6 Wire numbers = brackets: [6] Component / Pin # = parentheses: (1) Field components marked with * ● Green = voltage present ⠿ move DMM VDC -- V A A~ V V~ Ω ))) 10A VΩ▸ COM CR1 — YJ2N-LY DC24 (Bottom View) relay pulled · de-energized · Ω only ✥ 1 2 3 4 5 6 7 8 − + CR2 — 750R-2C-24V (Octal · Bottom View) relay pulled · bench test · Ω only ✥ 4 5 3 6 2 7 1 8 + − ▶ PUSH TO TEST screwdriver Drag probes to test points
🔒 Lock Out
🔓 Unlock
F1 — AGC 1A Fast-Blow
🔧 Remove Fuse
🔌 Install Good Fuse
🔌 Install Blown Fuse
💥 Simulate Overcurrent Blow
—
Generic DMM — Digital Multimeter
🔌 Install Good A-Fuse (11 A)
💥 Simulate A-Fuse Blow
📋 Show Meter Specs
🧮 Show Reading Basis
—
⚠ You should not measure resistance
on an energized circuit.
⚠ SAFETY WARNING
Circuit is ENERGIZED — disconnect before
removing fuse to avoid arc flash hazard.
CB2 — 0.5A Thermal Breaker
⚡ Simulate Trip
🔄 Reset Breaker
—
Component
—
🎓 Instructor — Fault Injection
⚡ Pitted-Contact Lab — intermittent faults
Actuate the contact repeatedly (toggle the switch / cycle the relay) — a soft pit only misbehaves ~1 in 4 makes. Test ≥10×. RCFA: high-resistance pitting traces to inductive-kick arcing.
Meter selection is in the Controls panel (top).  · orange meter-path overlay rides 🔋 Power Flow (Ω/cont/diode, DISC open)
Inject a fault to see its explanation here.

Each time a pitted contact closes, the sim rolls the dice to decide whether that particular make is a clean wipe or a degraded, high-resistance one (Soft misbehaves ~25% of makes, Med ~75%, Hard every time). That per-closure randomness is what makes an intermittent feel real.

Seeded (box checked). The dice run off a fixed starting number — the seed. The same seed reproduces the exact same sequence of good and bad makes every run. Use it for a live demo or a graded exercise so every student, and every replay, sees identical behavior. Type a different number and hit Reseed for a different — but still repeatable — sequence.

Free-random (box unchecked). The dice use the browser's true randomness, so every actuation is unpredictable and unrepeatable. This is the closest to a real nuisance fault — the "it worked last time, why not now?" experience.

Reseed. Restarts the sequence from the seed and clears the running good/bad tally for the selected contact, so you can replay the same run from the top.

Rule of thumb: seeded for teaching and scoring, free-random for realism. Either way, the resistance the meter reads is the exact resistance the solver used — nothing is faked.

OSHA 29 CFR 1910.334(b)(2) — Reclosing After Protective Device Operation

After a circuit is de-energized by a circuit protective device, the circuit may not be manually re-energized until it has been determined that the equipment and circuit can be safely energized.

The repetitive manual reclosing of circuit breakers or re-energizing circuits through replaced fuses is prohibited.

Overload Exception (the Note): When it can be determined from the design of the circuit and the overcurrent devices involved that the automatic operation of a device was caused by an overload rather than a fault condition, no examination is needed before re-energizing.

Source: 29 CFR 1910.334(b)(2), OSHA General Industry Electrical Standards

NFPA 70E-2024 — Electrically Safe Work Condition (ESWC)

Definition (Article 100): A state in which an electrical conductor or circuit part has been disconnected from energized parts, locked/tagged in accordance with established standards, tested for the absence of voltage, and if necessary, temporarily grounded for personnel protection.

Article 120.6 — Process for Establishing and Verifying an ESWC: The 2024 edition clarifies that absence-of-voltage testing must occur at each point of work. The 8-step process includes: identify all sources → open disconnecting devices → verify visually → apply LOTO → release stored energy → test for absence of voltage (live-dead-live) → ground if necessary.

Live-Dead-Live (Step 7): Use an adequately rated portable test instrument to test each conductor or circuit part at each point of work, both phase-to-phase and phase-to-ground. Before and after each test, verify the instrument operates correctly on a known voltage source.

Source: NFPA 70E-2024, Articles 100 & 120.6

24 VDC Context — The Honest Nuance

This trainer operates at 24 VDC — below the 50 V threshold referenced in OSHA 1910.333(a)(1). Electric shock risk is negligible under normal conditions.

However: The troubleshooting PROCEDURES taught here — LOTO, absence-of-voltage verification, systematic diagnosis before reclosing — apply identically to 480 V, 4160 V, or any voltage. Teach the right habits at safe voltages so they're automatic when the stakes are real.

Even 24 VDC can produce arc flash at high fault currents (battery banks, large DC bus systems) and can ignite flammable atmospheres.