Test 1 year 3
What is the maximum overload protection size for a 208-v three-phase, three-horsepower motor marked with a 1.12 service factor and a nameplate current of 11 amperes based on 430.32(A)? Assume this section will permit the motor to start and sizing per 430.32(C) is not warranted. (starting current is not a problem).
11x1.15= 12.65A
What is the maximum overload protection size for a 208-v three-phase, three-horsepower motor marked with a 1.15 service factor and a nameplate current of 11 amperes based on 430.32(A)? Assume this section will permit the motor to start and sizing per 430.32(C) is not warranted. (starting current is not a problem).
11x1.25=13.75A
What article deals with the sizing of busway taps?
368.17
Define Tap Conductor
A conductor, other than a service conductor, that has over-current protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.
What is a current limiting overcurrent protective device? What is their purpose? Is there only one?
A current limiting protective device is on that cuts off a fault current in less than one half cycle. To reduce damage to equipment and help protect workers from devastating arc flash and arc blast incidents.
Define Feeder
All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch circuit over-current device.
What is a solid-state device?
An electronic device that uses semiconductors to preform a function. It has no moving parts.
Define Ground Fault?
An unintentional, electrically conductive connection between an ungrounded conductor of an electrical circuit and the normally non-current-carrying conductors
Define overcurrent
Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit or ground fault.
Where is motor short circuit and ground fault protection typically installed in a motor branch circuit?
Beginning of the circuit
What are the 3 different categories of OCPD's?
Branch Circuit, Application Limited and Supplementary.
What are the two contexts branch circuit is used in the NEC and what do they mean?
Branch circuit are the conductors between the final over-current device protecting the circuit and the outlets. Over-current Protective Device and branch circuits are a device capable of providing protection for service, feeder, branch circuits, and equipment over the full range of over-currents between its rated current and its interrupting rating. such devices are provided with interrupting ratings appropriate for intended use but no less than 5000 amps.
Describe the normal, overload and fault operation of a circuit breaker. (thermal/magnetic)
Contacts are latched closed during normal operation, during an overload or fault the contacts become unlatched and open rapidly.
What is a mechanical device?
Device consisting of a piece of machinery that has moving parts that perform some function.
How is the interrupt rating of an OCPD calculated?
Equipment intended to interrupt current at fault levels shall have and Interrupting rating at nominal circuit voltage at least equal to the current that is available at the line terminals of the equipment.
What is the inrush current of a motor during the first half cycle and the following few seconds?
First half cycle 20 times, next few seconds 4-6 times
What should be checked during the period maintenance of a fuse?
Fuse Bodies, Fuse Mountings, Adjacent Conductors, Water Egress, and Cracking.
When checking the continuity/resistance of a fuse where should you place meter probes? Should this be done with the fuse installed on an energized circuit?
Get the continuity reading on either the blades or the ferrules, not on the case end caps.
How is the amperage rating of a conductor and OCPD calculated?
In general, the NEC requires service, feeder, and branch circuit conductor ampacity to be sized at least 125% of the continuous plus 100% of an non continuous load current. Conductors are to be protected by an OCPD at their ampacity, generally this is calculated the same way.
What is inrush current?
Inrush current is current when the motor is first turned on, it can be 20 times the normal current.
Where is separate overload typically installed in a motor branch circuit?
It can be anywhere in the circuit
What will happen to a fuse mounting clip if it has an undersized conductor, a loose connection, improper termination?
It will be exposed to excessive heat and will eventually cause the fuse to open or cause some other form of damage.
How is the needed voltage rating of an OCPD calculated?
Its not needed. The Voltage rating of an OCPD must be equal to or greater than the circuit voltage.
What is the physical rejection feature and what type of fuses have them?
Listed current-limiting fuses have physical rejection features that help prevent the installation of fuses that cannot provide a comparable level of protection for critical ratings and performance.
What are the three main categories of Circuit Breakers?
Molded Case circuit breaker, Insulated case circuit breaker, and low voltage power circuit breaker
What is special about a motor circuit protector?
Motor circuit protectors are circuit breakers devices that only have an instantaneous trip and are intended only for short circuit and ground fault protection of motor branch circuits. They do not provide overload protection.
Per NFPA 70E 225.3 should you immediately reset a tripped breaker? Why or why not?
No circuit breakers that interrupt faults approaching their ratings shall be inspected and tested in accordance with the manufactures instructions. It may need reconditioning replacement after interrupting a fault current near its marked interrupting rating.
Define overload
Operation of equipment in excess of normal, full load rating or of a conductor in excess of its ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is not an overload.
What is the purpose of an Overcurrent Protective Device? What can happen if they are misapplied?
Overcurrent protective devices are intended to prevent or minimize costly damage to transformers
How often should circuit breakers be inspected, tested and maintained?
Periodically, or manufactures recommendations
If a fuse is being replaced, what should the type and amp rating of the fuse be?
Proper and Correct rating
At what locations should available fault current be calculated?
Service Entrance, Switchgear, Switchboards, Transfer Switches, Panelboards, Load Centers, Motor Control Centers, HVAC Equipment, Disconnects, Motor Starters and Industrial Control Panels.
How is overload protection for a motor calculated? (separate overload device)
Service factor of 1.15 and less are 125%, temperature rise of 40 and more 125%, and all other 115% of the nameplate rating.
Single element, non time delay fuses protect against short circuits. What do dual element, time delays protect against?
Short circuits and Overloads.
How does the inverse time-current characteristic work?
The Higher the current level during a fault the faster the reaction time.
What is a Short Circuit?
The condition that occurs when an energized phase or ungrounded conductor comes into contact with another phase conductor, neutral or ground. Ground fault is a short circuit.
Define Service
The conductors and equipment connecting the servicing utility to the wiring system of the premises served.
Describe the basic or fundamental construction of a fuse.
The fundamental parts of basic fuse are comprised of a fusible link or links encapsulated in a tube compacted with fine granular material such as special silica sand and connected to contact terminals.
Define Available Fault Current.
The largest amount of current capable of being delivered at a point on the system during a short circuit condition.
What are the sources of fault current that are considered during a short circuit study?
Utility generation, local generation, synchronous motors, induction motors, batteries, energy storage systems and capacitors.
define the relationship between impeadence and amps
when impeadence goes down amps go up.
