Strand 4 (Electrical) — Circuits: Controls, Grounding/Bonding, Schematics, and Circuit Building

Control

Anything in an electrical system that starts, stops, protects, or regulates a load.

Electrical controls

Devices that directly open/close a circuit, often human-operated or with simple automatic sensing.

Electromechanical controls

Devices that use electricity to create motion (magnetism) to open/close contacts.

Solid-state controls

Devices that use semiconductors to switch or regulate electricity without moving parts.

Relay

A coil-operated switch often used for control logic or isolation.

Contactor

A heavy-duty relay designed for higher current loads like motors and heaters.

Switches

Devices that manually open or close contacts, including toggle, pushbutton, and selector types.

Thermostat

A device that opens/closes a contact based on temperature.

Float switch

A device that opens/closes based on liquid level.

Pressure switch

A device that opens/closes based on pressure.

Limit switch

A device that opens/closes when a mechanism reaches a specific position.

Grounding

Connecting part of the electrical system to earth to stabilize voltage and manage surges.

Bonding

Connecting metal parts together to ensure they are at the same electrical potential.

Equipment grounding conductor (EGC)

A conductor that bonds equipment enclosures/frames back to the source.

Bonding jumper

A short conductor used to bond around discontinuities.

Grounding electrode system

The part of the system that connects the electrical system to earth through electrodes.

Neutral

The grounded conductor that carries current during normal operation.

Ohm's law

The relationship defining voltage (V = I R), where V is voltage, I is current, and R is resistance.

Schematic diagram

A diagram showing electrical relationships using symbols.

Wiring diagram

A diagram showing physical connections, wire colors/IDs, and terminal numbers.

Ladder diagram

A schematic style common for control circuits, showing power rails and control logic.

Series circuit

A circuit topology where components are connected end-to-end so the same current flows through each component.

Parallel circuit

A circuit topology where components share the same two connection points, each receiving the same voltage.

Series-parallel circuit

A circuit that combines both series and parallel connections.

Test across component voltage

Confirming that the voltage measured across a component supports its expected behavior.

Current flow in series

The same current flows through all components in a series circuit.

Voltage in parallel

Voltage across each branch is the same in a parallel circuit.

Fault current path

The route that fault current takes to safely trip protection devices.

Control signal path

The route that a control signal follows to activate a device in a circuit.

Mechanical failure in relays

Failures that can occur, such as pitting or sticking of contacts.