Basics of Overcurrent
What is the main purpose of overcurrent protection devices?
To protect conductors, equipment, and people from overheating, fire, or shock.
What is an overload?
More current than normal load, but not a direct fault.
What is a short-circuit?
Current bypassing load and taking a low-resistance path.
Current flowing from hot to ground.
What does a fuse do when current is too high?
Metal strip melts, resulting in opening the circuit
Name one hazard caused by excessive current in a wire.
Overheating, fire, or damaged insulation.
Give one example of an overload situation.
Too many space heaters on one circuit.
What is the difference between bolted fault and arcing fault?
Bolted = direct contact
Arcing = current jumps through air.
Give an example of a ground fault
Hot wire touches a grounded metal box.
What makes a breaker different from a fuse?
It can be reset instead of replaced.
True or False: Overcurrent devices protect both equipment and people.
Do overloads cause damage instantly, or gradually over time?
Gradually
Which type of short creates plasma arcs?
Arcing fault
Ground Fault Circuit Interrupters GFCI
Which is "one and done": a fuse or breaker?
Fuse
What happens to the insulation of a conductor if it’s overloaded for too long?
It breaks down and may cause fire.
Which breaker mechanism responds to overloads?
Thermal Trip
Which breaker mechanism responds instantly to short circuits?
Magnetic trip
Why is a missing ground pin on a cord cap hazardous?
It removes the safe return path for faults
Name the two ways a breaker can trip.
Thermal (overload)
Magnetic (short circuit)
Why is it dangerous to “oversize” a breaker for a given wire?
The wire can overheat without the breaker tripping.
Why don’t breakers trip immediately during short overloads like motor starting?
They allow temporary surges before tripping.
A tool dropped across bus bars causing flash and bang is what fault?
Bolted short-circuit
How can a ground fault make a metal enclosure dangerous?
The enclosure becomes energized and can shock workers
Fuse vs Breaker analogy
Fuse is like a bullet (one time use)
Breaker is a resettable switch