Technical Sourcebook
Field-oriented guides on industrial motor control, wiring standards, and electrical theory. Each entry is paired with a simulator for hands-on practice of the concepts.
3-Wire Motor Control Circuit: Wire It in Your Browser
A 3-wire circuit latches through a seal-in contact, so the motor won't restart on its own after power loss. Trace it, then wire it in the free trainer.
How to Wire a Motor Starter (3-Phase, NEMA)
Power circuit, control circuit, seal-in contact, and OL protection — wire a NEMA Size 1 motor starter from L1 to T3. Free interactive wiring practice.
Motor Starter Internal Wiring: 3 Factory Jumpers
NEMA starters ship with three internal jumpers for coil return, seal-in, and OL protection. Where each one goes and why it matters.
NEMA vs IEC Overload Relay Placement Explained
The 95-96 OL contact sits on opposite sides of the coil in NEMA and IEC starters. Return-side vs hot-side — and the engineering reason behind each.
Motor Control Simulator — Wire Circuits Free in Your Browser
Wire motor control circuits from scratch in a free browser trainer. Route cables, press buttons, measure voltage with a multimeter, and find faults.
What Is a Contactor? The Switch Behind Every Big Load
What is a contactor? A magnetically operated switch that lets a small control signal run a big load. Coil, contacts, and what makes a starter different.
What Is a VFD? Wiring and Programming a PowerFlex 525
A variable frequency drive changes motor speed by changing frequency. See the run, direction, and speed terminals wired on a PowerFlex 525, then try it.
Measure Voltage on a Control Circuit: Step-by-Step
Anchor to L2 or X2, probe each terminal in sequence, find the open. Measurement procedure, reading interpretation, and free multimeter practice online.
How to Read a Ladder Diagram: Rails, Rungs, Contacts, Coils
Rails, rungs, contacts, coils: read a motor control ladder diagram from L1 to L2, trace current flow, and connect the schematic to the power circuit.
How to Reverse a 3-Phase Motor: Swap Two Leads
Reverse a 3-phase motor by swapping two phase leads at the load side. Why it works, the interlocks that prevent a phase-to-phase short, and OL placement.
Normally Open vs Normally Closed Contacts Explained
NO contacts close when actuated; NC contacts open. Why STOP is wired NC, START is wired NO, and how each contact's rest state decides circuit behavior.
Control Transformer Sizing: VA Load and NEC 430.72(C)
Size a control transformer by adding the VA draw of every secondary device, worst-case inrush included, then apply NEC 430.72(C) fuse sizing.
Jogging Circuit: Run the Motor Only While Held
A jogging circuit skips the seal-in, so the motor runs only while you hold the button. Compare the selector-switch and control-relay wiring methods.
Overload Trip: Why It Happened, How to Reset It
An overload trip means sustained overcurrent, not a short. What trips the relay, why the 95-96 contact opens, and how to find the cause and reset it.
Overload Relay Keeps Tripping: Diagnose It Now
OL relay keeps tripping? The relay is evidence, not the cause. Work through current draw, supply voltage, heater sizing, and ambient temperature.
Bump Test a Motor Starter: What the Manual Operator Does
A bump test closes the contactor by hand, bypassing the coil, to tell power-circuit faults from control-circuit faults. It also has clear limits.