Electrical Systems and Controls
Electrical Systems and Controls
This domain covers motors, starters, overloads, fuses, breakers, grounding, control circuits, sensors, transmitters, and basic PID control. The exam tests safe isolation and how a signal becomes a control action.
Core rules
- Lockout/tagout isolates energy and verifies absence of voltage before work.
- Overload protection protects motors from sustained overcurrent; fuses and breakers protect circuits.
- Grounding provides a fault path and supports protective device operation.
- A thermocouple generates millivolts; an RTD changes resistance with temperature; a transmitter often sends 4-20 mA.
- PID control uses proportional, integral, and derivative actions; integral removes offset.
Worked example
A transmitter has a 0-200°F range and a 4-20 mA output. At 12 mA, fraction of span = (12 - 4)/(20 - 4) = 8/16 = 0.50. Temperature = 0 + 0.50 x 200 = 100°F. Reason: the live zero at 4 mA distinguishes zero reading from a broken wire, and the span is 16 mA.
Traps
Do not assume a 0 mA signal means zero temperature; it often means a failed loop. Do not bypass overloads or grounds; do not tune PID before confirming sensor calibration; and do not work on energized controls without approved PPE and isolation.