NEC® FUNDAMENTALS
This NEC Article contains general requirements for overcurrent protection of conductors and equipment.
What is Article 240?
These are the standard ampere ratings for fuses and nonadjustable breakers, shown in NEC Table 240.6(A).
What are standard ampere ratings?
These two organizations set standards for testing and classifying fuses and breakers.
What are UL and NEMA?
Fused switches are available in these common voltage ratings.
What are 250V and 600V?
Overcurrent devices must be this—capable of being reached quickly without tools or ladders.
What is readily accessible?
Motor overload protection is typically sized at this percentage of motor full-load current.
What is 125%?
NEC 110.9 and 110.10 address these two characteristics that ensure overcurrent devices can safely interrupt fault current.
What are interrupting rating and protection against fault current?
A conductor with an ampacity of 115A may use this size overcurrent device per NEC 240.4(B).
What is 125 amperes?
This rating must be equal to or greater than the voltage of the circuit in which a fuse or breaker is used.
What is the voltage rating?
A switch marked “For Isolation Use Only” must not be operated under this condition.
What is under load?
The maximum height for the grip of a disconnect handle in its highest position.
What is 6 ft 7 in.?
An inverse-time circuit breaker protecting a motor may be sized up to this percentage of the motor FLC.
What is 250%?
This informational note says overcurrent protection opens the circuit if current reaches a dangerous temperature.
What is NEC 240.1 Informational Note?
The NEC allows using the next higher standard rated device only when the rating is at or below this value.
What is 800 amperes?
A 600V fuse can be used on a 208V system, but only if the device is rated for this type of current.
What is AC (or AC/DC depending on marking)?
Switches marked with dual horsepower ratings allow the higher rating only when using this type of fuse.
What are dual-element, time-delay fuses?
Overcurrent devices may not be installed in these four prohibited locations (name one).
What is in clothes closets / bathrooms (residential/guest rooms) / near easily ignitable materials / where exposed to physical damage / over stair steps? (any one correct)
This term refers to the idea that fuses/breakers protect the circuit from faults while overload relays protect conductors and windings.
What is a “systems approach”?
The NEC compares overcurrent devices to this safety component of a boiler.
What is a pressure relief valve?
For an overcurrent device above 800 amperes, the conductor must meet or exceed this characteristic.
What is the conductor ampacity?
Continuous loads must not exceed this percentage of the device rating unless the assembly is listed for 100%.
What is 80%?
Switches suitable for use as this must be marked “Suitable for Use as Service Equipment.”
What is a service disconnecting means?
Commercial buildings must allow occupants access to these devices for their branch circuits.
What are overcurrent devices (panelboards/breakers)?
Adjustable-trip breakers use this setting as their ampere rating when behind a locked door, sealed cover, or bolted enclosure.
What is the long-time pickup setting (adjusted trip setting)?
Articles 422, 430, and 440 each contain rules for overcurrent protection of these types of equipment.
What are appliances, motors, and air-conditioning equipment?
Three parallel 500-kcmil copper conductors (380A each) cannot be protected by a 1200A device; this smaller fuse size is acceptable.
What is 1100 amperes?
Dual-element, time-delay fuses may be sized up to this percentage of a motor’s full-load current for short-circuit and ground-fault protection.
What is 175%?
These heavy-duty switches are tested for use at 100% of rating and high available fault current, sometimes 100kA to 200kA.
What are fusible bolted pressure contact switches?
Outdoor-installed service disconnects must include this manufacturer-provided security feature when tampering is a concern.
What is a means for locking?
This NEC rule permits conductor protection to exceed ampacity only up to 800A and only if 3 conditions are met.
What is NEC 240.4(B)?