Third Year Code Practice Questions

Which of the following is not an objective of bonding?

To limit the magnitude of ground fault currents

Which of the following may compromise the impedance rating of the bonding path?

Loose locknuts where EMT is used as the bonding method

A service is fed with No. 3 AWG conductors in rigid metal conduit and is terminated to a 100 A, 75 degrees Celsius rated overcurrent device in the service box. Determine the minimum size of the copper service raceway bonding jumper.

No. 8 AWG

A 600 V motor control center (MCC) is supplied from an 800 A busbar installation. What is the minimum size of copper conductor required to bond the MCC enclosure?

No. 1/0 AWG

In an impedance grounded system, the ungrounded conductors must be insulated to the nominal _____ to _____ voltage of the system.

In an impedance grounded system the ungrounded conductors must be insulated to the nominal line-to-line voltage of the system

Where impedance grounded systems are used, warning signs indicating as such, and of the highest system voltage must be placed at:

Rule 10-306 1)

1. The supply source

2. The consumer’s service box or equivalent

3. The supply authority’s metering equipment

The minimum size of aluminum conductor required to connect the impedance grounding device to the system source shall be in no case less than ____ AWG

No. 10 AWG

The insulation value of the impedance grounding device must have an insultation voltage rating of not less than the ______ to ______ voltage of the system.

The insulation value of the impedance grounding device must have an insultation voltage rating of not less than the line to neutral voltage of the system.

An electrical system in which the circuit conductors have no direct connection to the circuit conductors of a supply authority system other than those established by grounding or bonding connections is known as a:

separately derived system

Three locations where the grounded conductor of a separately derived system operating at more than 750 V may be connected to the equipment bonding terminal are:

1. At the source

2. At the first switch controlling the system

3. At the tie point where two or more systems terminate at a tie point

A 347/600 V transformer may have the secondary grounded conductor bonded to the primary system grounding conductor through proper continuous EMT connection made up tight

True (Rule 10-212 2) )

What are the two different examples of equipment used to supply a separately derived system?

Rule 10-212 Appendix B

1. A generator to supply emergency power

2. A transformer used to supply a different voltage to parts of a facility

If ground rods are to be used as the grounding electrode, what is the minimum distance the rods must be spaced from each other?

3 m

What is the minimum size of conductor that can be used to connect to ground rods together

No. 6 AWG

Which conductor is required to be grounded in a 120/208 V three-phase, four-wire system?

The identified neutral conductor common to all phases

What is the minimum size of grounding conductor that can be installed for a 400 A, 120/208 V, three-phase, four-wire service? The service conductors are 600 kcmil RW90 conductors run in PVC conduit. Equipment is rated at 75 degrees

No. 6 AWG

What would be the minimum size of the field installed system bonding jumper be for the service for a 400 A, 120/208 V, three-phase, four-wire service? The service conductors are 600 kcmil RW90 conductors run in PVC conduit. Equipment is rated at 75 degrees

No. 3 AWG

Which of the following are not required to be connected to the grounding electrode for the purposes of equipotential bonding?

Interior isolated metallic water lines

A system that utilizes impedance grounding devices that serve line-to-neutral loads

Must trip immediately on the event of any system fault

Where is it permitted for the grounded circuit conductor in a 347/600 V three-phase, four-wire system to be connected to the grounding electrode via the grounding conductor if utilizing load side metering?

At the first service disconnecting means only

A three-phase 240 V, 30 A motor is fed with No.12 AWG conductors, and protected by a 90 A fuse. What is the minimum size of bonding conductor that can be used for this circuit? Equipment is rated at 90 degrees

No. 12 AWG

For transformers operating above 750 V used to provide different voltages in facilities, which of the following is not permitted as a method to connect the grounded circuit conductor to a separate grounding conductor?

The grounded conductor can be connected to the primary system grounding conductor with a field installed bonding conductor

What are the two types of overcurrent conditions?

1. Short-circuits

2. Overloads

A 15 A circuit breaker trips when a 20 A current flows through it for around two minutes. What time of overcurrent condition does this describe?

Overload

How does the protection offered by an overload device differ from the protection offered by an overcurrent device?

An overcurrent device is intended to open the circuit under both overload and short-circuit conditions

Which overcurrent device has electrochemical operation?

A circuit breaker

What is the most common type of short-circuit?

Ground faults

A Class A GFCI will trip when ground fault current reaches ______ mA, but will not trip if there is a ground fault current of ______ mA or less.

A Class A GFCI will trip when ground fault current reaches 6 mA, but will not trip if there is a ground fault current of 4 mA or less.

What type of arc-fault is considered a low-level fault?

A series arc-fault

What type of switch is not rated to be opened under load?

Isolating switch

What is the maximum available fault current that can be supplied from the secondary of a 350 kVA, 2400/240 V, single-phase transformer with a %IZ of 3%?

48 611 A

Which distribution system is also referred to as a ring system?

A network system

Which distribution system is typically used in residential areas?

A radial system

Which distribution system typically has high available fault currents?

A network system

Protective devices are required to operate automatically under two conditions. What are these conditions?

1. Overcurrent

2. Ground fault

What are the two current ratings required on all overcurrent devices?

1. Interrupting rating

2. Continuous current rating

What is the interrupting rating of an unmarked 90 A, 250 V circuit breaker?

5000 A

Overcurrent devices for four lighting branch circuits supplied from a single-phase, three-wire system are required to be inside a panelboard

True, a panelboard is required for two or more single-phase, three-wire lighting branch circuits. Rule 14-110 1) a)

What marking is used to identify a time-delay fuse?

Type D

What is the maximum continuous current rating for plug fuses?

30 A

Why can’t a Class H fuse be used to replace a Class K fuse?

Class H fuses have a lower interrupting rating than Class K fuses

A Class C fuse offers both overload and short-circuit protection

False, when Class C fuses are used, there must be a separate overload device. Rule 14-212 c)

What is the smallest rating of fused switch required for a 250 A fuse?

400 A fused switch

Describe how a circuit breaker reacts to open circuit during an overload condition

During an overload condition, the thermal element (bimetal strip) heats up and bends, unlatching the circuit breaker contacts

How many trip coils are required for a circuit breaker connected to a three-wire, single-phase ac circuit?

Two trip-coils

Under what conditions does a receptacle located within 1.5 m of a sink not require a Class A GFCI protection?

When the receptacle is intended for a stationary appliance and is located behind the appliance

GFCI receptacles can only function when there is no load connected to them

False, they must trip if there is a ground fault in the grounded conductor under no load conditions

How often should GFCIs be tested?

Once a month

What kind of protection does an outlet branch-circuit-type AFCI offer to upstream branch circuit wiring?

Series arc-fault protection

You may install a fuse that does not have an interrupting rating equal or greater than the available fault current of the circuit if it is approved as part of a series rated combination

False, only moulded case circuit breakers with a lower interrupting rating are permitted as part of an approved series-rated combination. Rule 14-014

A canopy switch controlling an incandescent lamp must have an ampere rating of twice the ampere rating if it is not T-rated.

False, a canopy switch must have rating at least three times the ampere rating of the load. Rule 14-508 c)

A 347 V light switch can be used to replace a defective 120 V light switch

False, box-mounted switches with different voltage rating are not interchangeable. Rule 14-512 3)

A contactor used to switch an inductive lighting load must have an ampere rating of twice the load ampere rating

True, a contactor must have a rating at least two times the ampere rating of the load. Rule 14-508 d)

A 347 light switch may be installed in a 2-gang box together with a 120 V switch if there is a permanent barrier between the two

True, switches are permitted to be grouped in the same enclosure if there is a permanent barrier. Rule 14-514

A manual, general-use switch controlling a 10 A, 120 V inductive load is required to have a 15 A minimum current rating

True, 15 A is the minimum current rating. Rule 14-510 2)

Solid-state devices are permitted to be used as isolating switches

False, solid-state devices are not permitted to be used as isolating switches or disconnecting means. Rule 14-700

What is the interrupting capacity of a breaker rated at 347 V, 60 A if it is unmarked?

10 000 A symmetrical

What is the calculated secondary short-circuit current of a 75 kVA, 600/208 V, three-phase transformer with an %IZ or 2.5%

8327 A

Which is the best term for a fuse that will allow up to 500% of continuous rated current to persist for up to 10 seconds?

A time-delay fuse

What is meant by the term trip-free when applied to a circuit breaker?

The breaker must trip, even if the handle is locked or held in the closed position

What is maximum value of ground fault current a Class A GFCI device will allow before actuating the internal tripping mechanism?

5 mA

Which 125 V, 15 A receptacle is exempted from the requirement of AFCI protection in a dwelling unit?

A refrigerator receptacle located in a kitchen

If two single-pole breakers are used to protect a 125 V, 15 A split receptacle fed from a multi-wire branch circuit, which of the following conditions must be observed?

Their handles must be interlocked together with a manufacturer-rated handle tie

A 200 A fusible switch is connected to a 600 A splitter with tap conductors that are 6 m in length. The splitter is fed with 700 kcmil RW90 conductors. The fusible switch supplies a 120 A non-continuous load. What is the minimum required size of the RW90 tap conductors from the splitter to the fusible switch? All conductors are copper, and all temperatures are rated at 75 degrees

No. 2/0 AWG

A tap conductor feeds a remote stop/start station for a motor. The motor is protected by a 90 A circuit breaker and is fed with No. 8 AWG R90. What is the minimum size of the R90 tap conductor for the stop/start station? All conductors are copper, and all terminations are rated at 75 degrees

No. 10 AWG

Which switch is not intended to establish or interrupt the flow of current to a device?

An isolation switch

What is a disadvantage of a network distribution system?

Lower values of impedance in the supply system

In which system is a circuit breaker allowed to have an interrupting rating less than the available fault current of the system?

A series rated system