Conductors with _ marked on the insulation are NOT approved for use in a wet location.
THHN
conductors with THHN insulation are approved for use in dry and damp locations only and conductors with THWN, THHW, and THW insulation are recognized for use in dry and wet locations.
Given: A one-family dwelling unit with a demand load of 200 amperes is supplied with a 120/240 volt, single-phase, electrical system from the local utility company. What is the MINIMUM size aluminum THW conductors required for use as service-entrance conductors for this residence?
4/0 AWG
one-family dwelling 120/240 volt, single-phase, service-entrance conductors to be sized at an ampacity of not less than 83% of the service rating. Therefore, 200 amperes x 83% = 166 amperes; size 4/0 AWG THW aluminum conductors with an allowable ampacity of 180 amperes should be selected for this dwelling.
Where a 150 kVA, single-phase transformer having a secondary voltage of 120/240 is installed at a multi-family dwelling, the full-load current rating, in amperes, of the secondary is _.
625 amperes
To find the full-load current rating of the single-phase transformer apply the single-phase current formula as shown:I = (150 kVA x 1000) / 240 volts = 15,000/240 = 625 amperes
Which one of the following listed circuit breakers is NOT a standard ampere rating?
75 amperes
the standard ampere ratings for fuses and circuit breakers. A circuit breaker with an ampere rating of 75 amperes is not a standard ampere rating.
The MINIMUM length of free conductor to be left at each junction box for the purpose of splicing conductors, or making connections to illuminares or devices shall be _ .
6 inches
free conductor is to be left at each junction box for splices or the connection of luminaires or devices. The intent of this rule is to ensure enough conductor slack for the terminal connections or splices to be made easily.
In general, overhead service-drop conductors shall NOT be smaller than _.
8 AWG copper
overhead service-drop conductors to be not smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum. Do not get service-drop conductors, the overhead conductors between the utility electric supply system and the service point, confused with the service-entrance conductors, the conductors from the service point from the utility company to the service disconnecting means.
When a galvanized eye-bolt is to be used as the point of attachment for an electrical service, the NEC requires the eye-bolt to be installed NOT less than _ above finished grade.
10 ft.
provide adequate vertical clearance of the conductors and prevent physical damage to the conductors and prevent persons from making accidental contact with the conductors which may create a shock hazard or electrocution. In no case shall the point of attachment of the service-drop conductors to be less than 10 ft. above finished grade.
Why is electrical continuity required for metallic conduit?
To establish an effective ground-fault path and facilitate the operation of the over-current protective device.
Electrical continuity is required for metallic conduit to establish an effective ground-fault path and facilitate the operation of the overcurrent protective device.
In dwelling units, receptacle outlets installed for countertop surfaces, must be located above, but NOT more than _ above the countertop or work surface.
20 inches
receptacle outlets installed for countertop or work surfaces in dwelling units may be located on or above, but not more than 20 in. above the countertop or work surface. The intent of this rule is to eliminate the use of unsightly extension cords (which reduces the amount of usable countertop space) on the countertop or work surface to supply cord-and-plug connected appliances. Also, receptacles located more than 20 inches above countertops or work surfaces may interfere with the cabinetry to be installed.
When conductors are installed in a conduit or tubing nipple of _ or less in length, the ampacity adjustment factors for more than three (3) current-carrying conductors in the raceway, are not required to be applied.
24 inches
adjustment factors for more than three (3) current-carrying conductors in raceways shall not apply where the raceway is not more than 24 inches in length. Where more than 3 current-carrying conductors are installed in short lengths of conduit or tubing, the heating effect caused from the additional conductors is insignificant therefore, the allowable ampacity of the conductors is not greatly reduced.
In compliance with the NEC, the total marked rating of a 120-volt, cord-and-plug-connected room air conditioner shall not exceed _ of the rating of a branch circuit when lighting units, general-use receptacles, or other appliances are supplied from the branch circuit.
50%
the special provisions for room air conditioners which are (1) rated not over 250-volts ac, single-phase and (2) which are cord-and-attachment plug connected. In order to prevent overloading the branch circuit, as per Section 40.62(C), the total rating of the A/C unit shall not exceed 50% of the rating of a branch circuit where lighting units, general-use receptacles or appliances are also supplied.
What shall not be located over the steps of a stairway?
overcurrent devices
“overcurrent devices shall not be located over steps of a stairway.” This requirement address a serious safety issue. No one should be required to stand on different treads on a stairway to replace, repair, maintain, install, troubleshoot, or reset overcurrent devices in a panelboard or switchboard located in a stairway.
Where a permanently installed outdoor swimming pool is located on residential or commercial properties, at least one (1) single-phase, 125-volt, 15- or 20-ampere receptacle shall be located not less than _ from and not more than _ from the inside wall of the swimming pool.
6 feet – 20 feet
apply to the installation of wiring methods and equipment in or adjacent to permanently installed swimming pools.
each permanently installed swimming pool is to be provided with at least one (1) single-phase, 15- or 20-ampere, 125-volt, receptacle placed not closer than six (6) feet from the pool and not more than twenty (20) feet from the pool.
This requirement allows ordinary appliances such as a radio, to be safely plugged in and used near the pool, but avoids the need for extension cords in the pool vicinity. Be advised the receptacles must be provided with
Metal water pipes installed in or attached to a building or structure shall be bonded to _.
a. the service equipment enclosure
b. the grounded conductor at the service
c. the grounding electrode conductor
d. any of the above
Any of the above
requires metal water piping systems to be bonded to any of (1) the service entrance enclosure, (2) the grounded conductor at the service, (3) the grounding electrode conductor.Where mechanical and electrical connections are within equipment, a failure of electrical insulation can result in the connected piping systems becoming energized. For example, an insulation failure in an electrical circuit of a water heater could energize the metal water piping.Metal water piping systems must be bonded so that when a fault occurs between an ungrounded (hot) conductor and the piping, the potential difference between the two is minimized, thereby reducing the risk of electrical shock.Also, note where installed in or attached to a building or structure, all metal piping systems, including gas piping, that is likely to become energized shall be bonded to a grounded source.
When armored cable, Type AC, is installed in an accessible attic and is run parallel to the sides of rafters, studs, or floor joists, _.
a. the cable shall be protected with running boards
b. the cable shall be protected by guard strips at least as high as the cable
c. either A or B
d. neither guard strips nor running boards shall be required
neither guard strips nor running boards shall be required
where the armored cable is installed parallel to the sides of rafters, studs or floor joists, neither guard strips nor running boards shall be required to protect the cable in accessible attics.
if the cables run across the top of the floor joists in an attic that is not accessible by permanent studs or ladders, protection of the cable is required where within six (6) feet of the nearest edge of the scuttle hole or attic entrance.
Generally, in a movie theater the manual switch for controlling the emergency lighting systems is permitted to be located _.
in an accessible location in the lobby
apply buildings used as a theater or for a similar purpose. Section 520.8 mandates the control of emergency systems in theaters to comply with the rules set forth in Article 700; Part V of Article 700 applies to the control of emergency lighting circuits. Section 700.21 does not permit a manual control switch for emergency lighting to be placed in a motion picture projection booth or on a stage or platform; the switch shall be located in the lobby or at a convenient accessible location.Emergency lighting systems are designed and installed to maintain a specific degree of illumination for means of egress of the building in the event of fire, or similar emergency, or if the normal power supply fails.
Single-conductor cable such as _ and single-conductor cable listed and identified as solar photovoltaic (PV) wire are permitted for use in PV source circuits within the PV array.
USE-2
690 covers the wiring methods specified for use on solar photovoltaic (PV) systems arrays.
indicates open, single-conductors such as Type USE-2 and single-conductor cable listed and identified as PV wire are permitted foruse in PV source circuits within the PV array.
These conductors are evaluated and listed for use where exposed to sunlight and wet conditions.
For dwelling units, GFCI protection is required for all single-phase, 125-volt, 15- and 20-ampere receptacles installed within six (6) feet of the top inside edge of the bowl of sinks located in _.
a. laundry rooms
b. bathrooms
c. garages
d. all of these areas
All of these areas
no matter what the location or room in a dwelling, where the 15- or 20-ampere, 125-volt eceptacles are installed within six (6) feet from the top inside edge of the bowl of the sink, GFCI protection must be provided to prevent a ground-fault shock hazard.
For a building or structure where the meter enclosure is adjacent to the service disconnecting means, it is permitted to ground the meter enclosure to the _ conductor on the load side of the service disconnect if ground-fault protection is not provided.
Grounded
The meter enclosure to be grounded by connection on the load side of the service disconnect where (1) no ground-fault protection is installed, (2) the meter enclosure is adjacent to the service disconnecting means, and (3) the grounded service conductor is not smaller than the size specified
In a dwelling unit where a 125-volt, 15- or 20-ampere receptacle is located under the counter for an in-sink waste disposer, the receptacle must be provided with _.
a. AFCI protection only
b. GFCI protection only
c. both AFCI and GFCI protection
d. neither AFCI nor GFCI protection
Both AFCI and GFCI protection
Because of the presence of water and grounded surfaces that contributes to a potential shock hazard
any 125-volt, 15- or 20-ampere receptacle installed within six (6) feet of a sink is required to be GFCI protected. Section 210.12(A) verifies AFCI protection is required for all 120-volt, 15- or 20-ampere branch-circuits that supply outlets in kitchens in dwellings.AFCI devices are designed to determine resistance to unwanted tripping due to the presence of arcing that occurs in utilization equipment under normal operating conditions or to a loading condition that closely mimics an arcing fault.
Where a 125-volt, 15-ampere receptacle is connected to a 120-volt branch circuit supplying two (2) or more receptacles or outlets, the maximum permitted cord-and-plug-connected load to the receptacle is _.
12 amperes
the general rules regarding branch circuits. Branch circuit and receptacle ratings are addressed in Part II of Article 210. To prevent overheating receptacles, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 21(B)(2), where connected to a branch circuit supplying multiple receptables or other outlets. This table shows a 15-ampere rated receptacle may carry a maximum cord-and-plug-connected load of 12 amperes under this condition.
In industrial establishments only, when a 200-ampere rated busway is tapped from a 600-ampere rated busway, what is the maximum permitted length of the 200-ampere busway where overcurrent protection is not provided for the 200-ampere busway?
50 ft
the permitted installation of busways. For busways in industrial establishments only, providing overcurrent protection at the point where the busway size is changed is not required if the busway having the smaller ampacity does not exceed fifty (50) feet in length and has an ampacity of at least one-third the rating of the overcurrent protection of the larger usway. 1/3 of 600 amperes = 200 amperes
When installing nonmetallic sheathed cable enclosed in an underground buried PVC conduit, the cable _.
a. must be Type NMC
b. must be Type NMS
c. must be Type NMW
d. is prohibited
Is prohibited
he inside of all raceways and enclosures located underground is classified as a wet location. The conductors and cables installed in underground installations must be of a type listed for use in wet locations.Restrictions of the use of non-metallic sheathed cable
NMC is permitted in dry, moist, and damp locations, but wet locations are not included in this list.
According to the NEC, fixed outdoor deicing and snow melting equipment is to be considered as a _ load.
Continuous
a continuous load is a load expected to continue for three (3) hours or more.The installation requirements for fixed outdoor electric deicing and snow melting equipment, fixed outdoor electric deicing and snow melting equipment shall be considered a continuous load.When sizing conductors and overcurrent protection for the fixed outdoor equipment you must take into consideration the equipment can operate over 3 hours, so it is considered a continuous load.
In regard to a commercial building, where a service-entrance conduit having a length of six (6) feet contains four (4) size 2 AWG THWN insulated copper current-carrying conductors, each of the conductors have an allowable ampacity of _.
92 amperers
To solve this problem first locate the conductor size,and look under the copper THWN column with a temperature rating of 75°C and note the ampacity of the conductors is 115 amperes. The table is based on an ambient temperature of 86°C and not more than 3 current-carrying conductors in the raceway.
in this situation there are 4 current-carrying conductors in the raceway therefore, we must apply the correct adjustment factor (derating value)
2 AWG THWN ampacity = 115 amperes (before derating)115 amperes x 80% (adjustment factor) = 92 amperes
What material should not be used for Grounding electrodes.
Aluminum
For a 300 ampere electrical circuit, what is the minimum size copper equipment grounding conductor as per NEC?
4 awg
4 AWG is the minimum size wire for a 300 ampere circuit
What is the minimum size secondary conductor required for a 2 wire 480 volts/ 120 volts transformer rated at 2.3 KVA with 750C temperature at terminals?
14 AWG
Secondary transformer current = 2300 / 120 = 19.16 amperes
The suitable conductor is 14 AWG with 20 amperes capacity at 750C
What is the resistance of the conductor if the conductor voltage drop is 3.6 volts and current flowing through conductor is 18 amperes?
0.2 ohms
Conductor voltage drop = 3.6 volts
I R = 3.6 volts
R = 3.6 / 18 = 0.2 ohms
When an electrical circuit tested with ohmmeter, a short circuit is indicated by a reading of ………………….
Zero
For stationary small motors rated less than ………………, the branch circuit over current device may serve as a controller.
1/ 8 horse power
What is the demand factor applied in calculating feeder or service conductor load for a commercial kitchen having four electrical equipment
80 %
Demand factor for kitchen equipment in other than dwelling unit shall be applied according to 220.56 table.
A 440 volts motor has a full load current of 34 amperes. what size disconnecting means is required?
40 amperes
The rating of disconnecting means is 115% of full load current.34 * 1.15 = 39.1 amperes.The nearer rating is 40 amperes.
If two 4 ohm resistors are connected in series which are powered by 240 volts power source, what is the current flow across one 4 ohm resistor?
30 amperes
Total resistance of the circuit = 4 + 4 = 8 ohms
Current flow in the circuit = 240 /8 = 30 amperes
In series circuit flow in the circuit elements is same. so 30 amperes current will flow in both series resistors.
What is the minimum size of THWN conductors required for single phase 10 HP motor connected to 240 volts supply?
6 AWG THWN Copper
FLI current of single phase 10 HP motor at 230 volts = 50 amperes
Minimum conductor ampacity = 50 * 125% = 62.5 amperes
6 AWG THWN Copper with 65 amperes capacity at 75 0C is suitable conductor for the motor
In a metal wire-ways, the distance between supports shall not exceed ………….. ft.
10
Underground wiring shall be installed in which of the following conduit
a.)Threaded rigid metal
b.)Threaded steal intermediate metal
c.)All options are correct
.)PVC
All options are correct
What is the resistance of 80 watt Light bulb rated at 120 volts?
180 ohms
When branch circuits used at outside, the size of overhead conductors for 600 volts or less, for spans upto 50 feet, shall not be less than …………. copper.
NO 10
For Copper it is NO.10for aluminum it is NO 8
All 15,20 amperes receptacle outlets installed in bathrooms of dwelling units shall always require …………………………………….
Ground fault circuit interceptor
If the panel board rating is 100 amperes, what shall be the over current device rating located in panel board?
less than 100 amperes
The over current device rating must not be greater than panel board rating in which it is located
If a 230 volts load is connected to 240 volts power source, what is the minimum voltage that can be supplied to load as recommended by NEC?
228 volts
When the single phase air conditioner rating is less than ………. at 240 volts can be considered as single motor unit in determining branch circuit conditions.
40 amperes
What is the low voltage contact limit for sinusoidal AC?
15 Volts RMS
Flexible cards may not be used in the following locations ……….
To replace a fixed wiring of a structure
What is the minimum percentage rated voltage that a storage battery should supply the emergency load?
87 1/2 %
The vertically run metal wire-ways shall be surely supported at intervals not exceeding …………. ft of wire way and shall not have more than one joint between supports.
15
The interior of any dip tank can be considered as ………………. location
Class1, Division1
Should ungrounded ducts or conduits should be sealed before entering buildings?
yes, to prevent unwanted gases entry in buildings
A continuous load is load where the maximum current is expected to continue for ………… hours or more.
3