Course Objective
Fires and equipment damage due to electrical faults or overload can be prevented by proper electrical device application. Protective devices, such as fuses and circuit breakers, must be sized to both isolate and limit short circuit faults. Improperly applied protective devices can explode under these same conditions. Overload protective devices are required in almost every motor circuit, yet one of the most common causes of motor failure is overload. The student will be equipped to make decisions that are prudent, yet still assure plant protection.

Benefits
Updates on NEC requirements for protective devices
Reduced motor failures

Activities
Choosing the right fuse for the job
Circuit breaker and overload sizing and replacement
Testing a circuit breaker and overload protective device for the job

Outline

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Short Circuits vs. Overloads
Limiting the Effects of Short Circuits
Equipment Fault Current Ratings
The X/R Ratio as stated in the National Electrical Code?
"Back-of-envelope" Short Circuit Calculations

Low Voltage (less than 1000 volts) Fuses
Fuse Construction and Fuse Types
UL Fuse Classes and Voltage Ratings
Sizing Fuses for Industrial Circuits
Time Vs. Current Characteristics for Fuses
Device Selectivity
Classroom Exercise

Molded Case Circuit Breakers
Circuit Breakers vs. Fuses
Circuit Breaker Components
Molded Case Breaker Trip Types
The Reasons for Fused Breakers
Key Requirements when Replacing a Breaker
Testing Breakers - Overcurrent and Megohm Tests
Classroom and Exercises
Breaker Ratings
Symmetrical and Asymmetrical Fault Current

Motor Overload Protection
Motor Losses and Heating
Insulation Class and the Insulation Life Formula
The Motor Destruction Curve
Thermal Overload Protection in a Motor Circuit.
Three Types of Protection
Overload Protection Types
Internal Protection
Bimetallic, Solder-Ratchet, and Electronic Overload Relays
Ambient Compensation
Sizing Motor Overload Heater Elements
Classroom Exercise and Field Demonstrations
Protective Device Coordination