Code level 3 test prep

Branch circuit overcurrent protective device

"overcurrent protective device, branch circuit" as a device capable of interrupting overcurrents between its rated current up to its interrupting rating.

Overloads are most often between ____and ___ times the normal operation ampacity of the conductor and equipment.

1&6

Three important categories of overcurrent protective devices are:

1) Branch-circuit overcurrent protective devices 2)Application limited overcurrent protective devices that are suitable for specific branch circuit applications under limited conditions per the NEC (often listed or recognized for the specific use) 3)Supplementary overcurrent protective devices

Ground-fault ampere pick-up settings from to amperes

100 1200

______ requires ground-fault protection of equipment to be performance tested when installed.

230.95(c)

Supplementary OCPDs can only be used in compliance with ________, which does _______using supplementary OCPDs in place of branch circuit OCPDs.

240.10 not permit

The NEC defines a current-limiting overcurrent protective device in?

240.2.

Section ______ requires a branch-circuit overcurrent protective device in each ungrounded circuit conductor and located where the conductors receive their supply.

240.21

The 10 Foot Feeder Tap Rule

240.21(B)(1) Feeder Taps Not over 3 m (10 ft) Long. If the length of the tap conductors does not exceed three meters (10 feet) and the tap conductors comply with all of the following: (1) The ampacity of the tap conductors is Not less than the combined calculated loads on the circuits supplied by the tap conductors, and Not less than the rating of the equipment containing an OCPD(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors. Reference the NEC for an exception to 240.21(B)(1)(b).

The 25-Foot Feeder Tap Rule

240.21(B)(2) Taps Not over 7.5 m (25 feet) Long. Where the length of the tap conductors does not exceed 7.5 m (25 feet) and the tap conductors comply with all of the following: (1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors. (2) The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side. (3) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

lists the standard ampere ratings for fuses and inverse time circuit breakers.

240.6

Table to find FLA in the NEC

430.247-430.250 depending on the motor

Where to find overload formula for motors

430.32(a)(1)

Table for percentage of FLA

430.52

Table for transformer ocpds

450.3(b)

Every circuit breaker having an interrupting rating other than ______shall have its interrupting rating shown on the circuit breaker. The interrupting rating shall not be required to be marked on circuit breakers used for supplementary protection.

5,000 amps

Bolt fault

A bolted fault condition represents a "solid" (bolted or welded) connection of relatively low (or assumed "zero") impedance.

Tap Conductor

A conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.

Instantaneous Trip (as applied to circuit breakers)

A qualifying term indicating that no delay is purposely introduced in the tripping action of the circuit breaker.

Adjustable (as applied to circuit breakers).

A qualifying term indicating that the circuit breaker can be set to trip at various values of current, time, or both, within a predetermined range.

Nonadjustable (as applied to circuit breakers)

A qualifying term indicating that the circuit breaker does not have any adjustment to alter the value of current at which it will trip or the time required for its operation.

Inverse Time (as applied to circuit breakers)

A qualifying term indicating that there is purposely introduced a delay in the tripping-action of the circuit breaker, which delay decreases as the magnitude of the current increases.

OCPDs are separately rated for _____and _____voltage

Ac Dc

Types of Circuit Breaker

Adjustable Instantaneous Trip Inverse Time Nonadjustable

Arcing fault

An arcing fault condition does not have a solid bolted connection between conductors or buses. Instead, an arcing path through air between conductive parts with an associated arc resistance is present.

Supplementary overcurrent protective devices

Are application limited Not permitted to be used as a substitute for a branch-circuit OCPD or where a branch-circuit OCPD is required (240.10) Typically permitted to be used in control circuits, appliances, and luminary applications Very limited in their capabilities Have different product standard requirements as compared to branch-circuit OCPD product standards

Types of short circuit

Bolt and arcing

Application limited overcurrent protective devices that are suitable for specific branch circuit applications under limited conditions per the NEC (often listed or recognized for the specific use)

Can only be used where the NEC permits and where the OCPD is suitable May be very limited in their capabilities; they may be suitable for a particular, limited application, but not suitable for another application

Why Current-Limiting OCPDs Reduce Damage

Current-limiting OPCDs provide superior short-circuit protection by reducing thermal and mechanical stresses on conductors and equipment. The greatest damage done to components by a fault current often occurs in the first 1∕2-cycle.

Where to test a fuse

For ferrule fuses, place the test probes on the metal ferrules. For knife blade fuses, place the test probes on the metal blades, not on the fuse end caps.

When do you use the neck for motor ocpds

For ground fault protection

When do you use the name plate for ocpds

For overload protection

240.60(C) Marking

Fuses shall be plainly marked, either by printing on the fuse barrel or by a label attached to the barrel showing the following: (1) Ampere rating (2) Voltage rating (3) Interrupting rating where other than 10,000 amperes (4) Current limiting where applicable (5) The name or trademark of the manufacturer

A _______ is created when a path from one or more phase conductors to ground is created. All ground faults are short circuits, but not all short circuits are ground faults

Ground fault

Interrupting rating is often denoted as ?

IR

Branch-circuit overcurrent protective devices

Intended for protection of a service, feeder or branch circuit of an electrical system Capable of being able to provide a full range of overcurrent protection from rated current to its interrupting rating Interrupting rating sufficient for the application

Transformer formula

KVA x 1000 / primary voltage Answer ^ X percentage for 450.3(b)

Classes of fuses

L J R RK1 RK5 CF cc T G K H plug

An arcing fault current is always ____ than the available bolted fault current value

Less

The greater the overcurrent as a percentage of the rated current the ____ time it takes to reach damaging temperature levels.

Less

How to test a fuse

Make sure the circuit is de-energized then removing both indicating and non-indicating fuses from the circuit, and checking them for continuity by resistance measurement

Ground fault formula

NEC FLA X fuse percentage

Overload formula

Name plate FLA X motor service rating

Can you tap a tap

No

the NEC ______ selecting the "next standard ampere rating" in certain applications.

Permits

Circuit breakers ________be reset after a fault interruption without some investigation and possibly additional steps

Shall not

Interrupting Rating

The highest current at rated voltage that a device is identified to interrupt under standard test conditions.

Setting (of circuit breakers)

The value of current, time, or both, at which an adjustable circuit breaker is set to trip.

Tip for remembering what a tap is.

When you upsize the wire for volatage drop to the first j box

Supplementary protective devices can only be used as ..........

additional protection when installed on the load side of a branch-circuit overcurrent device

overload current

an excessive current relative to normal operating current, but one that is confined to the normal conductive path provided by the conductors, circuit devices, and loads of the distribution system

An OCPD must ____________ the destructive energy of short-circuit currents in the process of interrupting

be able to withstand

Many OCPDs are not considered ?

current limiting.

The voltage rating of the OCPD must be ________ than the circuit voltage

equal to or greater

Ground fault

ground fault is a type of short-circuit having an unintentional connection between an ungrounded conductor and a non-current carrying conductor, metallic equipment, or earth

Overcurrent

identified as either an overload current or a short-circuit current, which often is referred to as fault current.

Potentially harmful overloads can result from ?

improperly designed or operated equipment, worn equipment, or too many loads on one circuit

A sustained overload current results ?

in the overheating of conductors and other devices and can cause deterioration of insulation, which may eventually result in severe damage, fires, and short-circuits if not interrupted fast enough to prevent damage.

Short circuit

not defined in the NEC. However, one generally accepted definition of short circuit is when a phase or ungrounded conductor comes into contact with another phase conductor, neutral, or ground, such line-to- line (L-L), line-line-line (L-L-L), line-to-neutral (L-N), or line-to-ground (L-G).

A current-limiting protective device is one which cuts off a fault current in less than ?

one-half cycle

Supplementary OCPDs

provides limited protection, in addition to the branch circuit OCPD which must be installed in the branch circuit

Ground faults are considered a type of ?

short circuit

Typical fusible equipment include

switchboards, distribution panelboards, motor control centers (MCCs), and industrial control panels.

Harmless overloads routinely are caused by?

temporary inrush or surge currents which occur when motors are started or transformers are energized. Such temporary overload currents are normal occurrences.

Most ground faults occur due ?

to a breakdown in insulating material (including air) of a phase conductor near a grounded reference.

When applying OCPDs, there are three ratings which must be selected.

voltage, ampere, and interrupting ratings