Electrical Trade Knowledge (Industrial Journeyman Electrician)
Industrial systems and equipment
Industrial questions emphasize motor circuits, motor control, hazardous locations, grounding and bonding of equipment, transformers, and power distribution. You should be comfortable with motor nameplate data, overload versus short-circuit protection, controller disconnects, and the classification of hazardous (classified) locations.
Concepts to master
- Motor branch circuits: conductor sizing at 125% of table current, overload protection sized to nameplate, short-circuit protection per the applicable tables.
- Disconnects and controllers: a motor disconnecting means within sight, controller location, and remote-control provisions.
- Hazardous locations: Class I/II/III, Division 1 vs. 2, Zone systems, and the concept of intrinsic safety.
- Grounding and bonding: equipment grounding conductors, bonding jumpers, and grounding electrode systems in industrial settings.
- Transformers and distribution: dry-type vs. liquid-filled, ventilation, and secondary conductor protection.
Traps to expect
Examiners love the overload-versus-short-circuit distinction: overload protection protects the motor, short-circuit protection protects the circuit. Also watch for nameplate versus table current (use nameplate for overloads, table for conductors). Hazardous-location items test whether you can match a material (gas, dust, fiber) to the correct class and division. Disconnect "within sight" wording is a frequent distractor.
Worked example
A 25 hp, 460 V, three-phase motor has a nameplate FLA of 34 A. Branch-circuit conductors must have ampacity of at least 34 × 1.25 = 42.5 A. Overload protection is sized from the nameplate FLA, not the table value, and the short-circuit protection is selected from the motor short-circuit tables. If the disconnect must be within sight, confirm the distance and line-of-sight requirement.
Rule of thumb
Conductors use table current × 125%; overloads use nameplate current. Keep those two sources straight and most motor questions fall into place.