Electrical Level 2 Module 10 Circuit Breakers and Fuses

Overloads are most often between __ and __ times the normal current level.

1, 6

Generally, the ampere rating of a fuse and switch combination should be selected at ______ of the load current.

125%

A dual-element fuse is generally permitted to be sized up to _____, and a non-time-delay fuse up to _____ of the motor full-load amperes

175%, 300%

Cartridge fuse- Class R:

250/600A, interrupting rating of 200,000 rms symmetrical; listed as current limiting.

Cartridge fuse- Class H:

250/600V, 1-600A, interrupting rating of 10,000 rms symmetrical.

Cartridge fuse- Class K:

250/600V, 1/10-600A, interrupting ratings ranging from 50,000 to 200,000 rms symmetrical.

Cartridge fuse- Class J:

600V, 1-600A, interrupting ratings ranging from 200,000 to 300,000 rms symmetrical; listed as current limiting.

Cartridge fuse- Class CC:

600V, 1/10-30A, interrupting rating of 200,000 rms symmetrical; listed as current limiting.

Cartridge fuse- Class L:

600V, 601-6,000A, interrupting ratings ranging from 200,000 to 300,000 rms symmetrical; listed as current limiting.

Molded-case circuit breaker:

A circuit breaker enclosed in an insulating housing.

Circuit Breaker:

A device that is designed to open a circuit automatically at a certain over-current. It can also be used to manually open and close the circuit.

Cartridge Fuse:

A fuse enclosed in an insulated tube to confine the arc when the fuse blows.

Nonrenewable fuse:

A fuse that must be replaced after it interrupts a circuit.

What is likely the cause of a majority of circuit breaker failures?

Heat

NEC Section 110.3(B)

Installation and Use: Listed or labeled equipment shall be used and installed in accordance with any instructions included in the listing or labeling.

NEC Section 110.9

Interrupting Rating: Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage not less than the current that must be interrupted.

NEC Section 240.83(C)

Interrupting Rating: Every circuit breaker having an interrupting rating other than 5,000A shall have its interrupting rating shown on the circuit breaker.

Where in the NEC would you find information on circuit breaker applications?

NEC Section 240.85

Plug fuse- TL series:

Normal-duty motor loads.

Plug fuse- W series:

Residential loads and nonmotor industrial circuits.

Short circuit:

The current that exists when an unintended path is created between any two components in a circuit.

Fault Current:

The current that exists when an unintended path is established between an ungrounded conductor and ground.

Fuse Link:

The fusible part of a cartridge fuse.

Edison-base type fuses are only permitted as replacements in existing installations;

all new work must use Type S fuses in accordance with NEC Section 240.51(B).

If a fuse is used with a voltage rating lower than the circuit voltage,

arc suppression will be impaired and, under some fault current conditions, the fuse may not safely clear the overcurrent.

The voltage rating of a fuse must be

at least equal to the circuit voltage.

If this fault current exceeds the interrupting rating of a fuse or circuit breaker, the protective device can be

damaged or destroyed; such current can also cause severe damage to equipment and injure personnel.

The circuit breaker current rating must be

equal to or less than the load circuit conductor current-carrying capacity (ampacity).

All fuses have an inverse time-current characteristic. The fuse will open

quickly on high currents and after a period of time delay on low overcurrents.

Cartridge fuse- Class T:

300/600V, 1-1,200A, interrupting rating of 200,000 rms symmetrical; listed as current limiting.

Cartridge fuse- Class G:

480V, 1-60A, interrupting rating of 100,000 rms symmetrical; listed as current limiting.

Dual-element fuse:

A fuse having 2 fuse characteristics; the usual combination is an overcurrent limit and a time delay before activation.

Frame size:

A method used to classify circuit breakers according to given current ranges.

Fuse:

A protective device that opens a circuit when the fusible element is severed by heating due to a fault current or overcurrent passing through it.

Plug Fuse:

A type of fuse that is held in position by a screw thread contact instead of spring clips, as is the case with a cartridge fuse.

Overcurrent protection:

De-energizing a circuit whenever the circuit exceeds a pre-determined value; the usual devices are fuses, circuit breakers, or magnetic relays.

Pole:

The portion of a device associated exclusively with one electrically separated conducting path of the main circuit or device.

Edison-base:

The standard screw base used for ordinary lamps and Edison-base plug fuses.

Switched neutral breaker:

This breaker disconnects the neutral or grounded conductor simultaneously with all ungrounded conductors. Breakers that switch grounded conductors are used in fuel dispensing equipment as described in NEC Section 514.11.

Shunt trip circuit breaker:

This breaker has a built-in electrical coil that causes it to open the breaker contacts when the coil is energized by an outside source. (Sources include fire suppression circuits, pushbuttons, or alarm circuits.)

Non-Automatic breaker/ Molded-Case switch:

This breaker has no devices to protect the circuit against overcurrent. It is used as a manual disconnect by operating the handle. (Similar to a non-fused disconnect switch.)

GFCI breaker:

This breaker includes circuitry to monitor currents on both conductors in the circuit. If there is an imbalance of those currents of 6mA or more, the breaker will operate and open the circuit.

Arc fault circuit breaker:

This breaker includes electronic circuits to monitor current flow within the breaker. If it detects a pattern of small continuous surges or spikes in said current flow the breaker will operate and open the circuit.

Plug fuse- S series:

Time delay fuses with tamper-resistant dimensions to prevent substitution of incorrect fuses.

NEC Section 240.83(E)

Voltage Marking: Circuit breakers shall be marked with a voltage rating that is not less than the nominal system voltage that is indicative of their capability to interrupt fault currents between phases or from phase to ground.

Plug fuse- T series:

When extra time delay or sensitivity to temperature is needed.

An overcurrent protection device must be selected with an interrupting capacity that is

equal to or greater than the available short circuit current at the point at which the circuit breaker or fuse is applied to the system.

Type S fuses

have different base sizes with matching adapters with 15 classifications from 0-30A.

Edison-base fuses

have the same size base no matter the rating 0-30A.

Once a plug fuse has opened a circuit for a fault or overload, for a safe and effective restoration,

it must be replaced by a new fuse of the same rating and characteristics.

The rated continuous current of a device is the

maximum current (in amperes) that it will carry continuously without exceeding the specified limits of observable temperature rise.

The amperage interrupting capacity (AIC) of a circuit breaker is the

maximum short circuit current at which the breaker will safely interrupt the circuit.

The ampere rating of a fuse should

normally not exceed the current-carrying capacity of the circuit.