Unit 8: Single Family Dwelling Service Calculations Flashcards
Using NEC® demand factors and load calculation methods to determine the appropriate service size, conductor sizing, and overcurrent protection for single-family dwellings. (25 cards)
Fill in the blank:
When determining the initial standard size time-delay fuses for branch-circuit, short-circuit and ground-fault protection for a three-phase, continuous-duty, squirrel cage, ac motor, the fuses shall have a rating of _____ of the full-load current rating of the motor. When the value determined does not correspond to a standard ampere rating, the next higher standard rating shall be permitted.
175 percent
Fill in the blank:
Given: A junction box to be installed will contain five (5) size 12 AWG conductors and six (6) size 10 AWG conductors. The junction box is required to have a volume of at least _____.
26.25 cu. in.
Size 12 AWG – 2.25 cu. in x 5 wires = 11.25 cu. in.
Size 10 AWG - 2.50 cu. in. x 6 wires = 15.00 cu. in.
TOTAL = 26.25 cu. in.
Neon sign equipment having an open circuit voltage exceeding how many volts shall not be installed in or on dwelling occupancies?
1000 volts
What minimum size wire-type equipment grounding conductor is required for a 240-volt, single-phase, 10 kW residential electric range?
10 AWG
Fill in the blank:
Where the NEC specifies that one equipment shall be within sight of another equipment, the specified equipment is to be visible and not more than _____ distant from the other.
50 feet
Fill in the blank:
All 125-volt, single-phase, 15- and 20-ampere receptacle outlets in a dwelling must be installed in habitable rooms so that no point along the floor line is further from an outlet than _____.
6 feet
Fill in the blank:
Luminaires mounted in walls of permanently installed swimming pools shall be installed with the top of the luminaire lens not less than _____ below the normal water level of the pool, unless the luminaire is listed and identified for use at lesser depths.
18 inches
Fill in the blank:
Where there is no overcurrent protection on the secondary side of a 480-volt transformer with a primary current of 100 amperes, the rating of the primary overcurrent protective device should not exceed _____.
125 amperes
Fill in the blank:
For the purpose of maintaining and servicing a 3-phase, 208Y/120-volt switchboard, a clear working depth distance of _____ must be maintained in front of the switchboard.
3 feet
Fill in the blank:
Where a permanently installed generator is installed as a separately derived system, _____ must be provided.
system bonding jumper
Fill in the blank:
Type AC cable shall provide an adequate path for _____.
fault-current
Fill in the blank:
Mandatory rules of the NEC are those that identify actions that are specifically required or prohibited are characterized by the use of the terms _____.
shall or shall not
For a direct burial feeder cable to a water well pump located 50 feet from a dwelling, which of the following listed wiring methods is approved for such use?
a. Type NM cable
b. Type AC cable
c. Type TC cable
d. Type UF cable
d. Type UF cable
All of the following wiring methods are permitted in a ceiling space used as a return-air plenum except:
a. Type AC cable.
b. rigid PVC conduit.
c. intermediate metal conduit (IMC)
d. Type MI cable.
b. rigid PVC conduit
Fill in the blank:
A 240-volt, single-phase 10 kW commercial dishwasher will draw _____ of current.
42 amperes
Single-phase current formula
I = power ÷ volts
I = 10,000 watts = 41.6 amperes
240 volts
Fill in the blank:
A type of fuse not permitted for new installations and shall be used only for replacements in existing installations is a/an _____ fuse.
Edison-base
Fill in the blank:
The _____ flexible cord is permitted to be immersed in water to supply a permanently installed fountain at an amusement park.
Type SOW
Fill in the blank:
Where cord-and-plug connected appliances are likely to be used simultaneously, each _____ or fraction thereof of fixed multioutlet assemblies used in other than dwelling units, shall be considered as an outlet of not less than 180 volt-amperes.
12 inches
Fill in the blank:
All 15- and 20-ampere, single-phase, 125-volt receptacles located within at least _____ of the inside walls of a permanently installed swimming pool must be protected by a Class A ground-fault interrupter.
20 feet
Fill in the blank:
A point on a wiring system at which current is taken to supply luminaires, appliances, heaters, motors and similar current-consuming equipment is considered a/an _____.
outlet
Fill in the blank:
T The number of 120-volt, 15-ampere, general lighting branch circuits required for a dwelling with 70 feet by 30 feet of habitable space is _____.
four
70 ft. x 30 ft. = 2100 sq. ft. x 3 VA = 6300 VA (house load)
120 volts x 15 amperes = 1800 VA (one circuit)
6300 VA (load) = 3.5 = 4 general lighting circuits
1800 VA (circuit)
Fill in the blank:
Given: A branch circuit supplies a single hermetic refrigerant motor compressor, with a FLC rating of 18 amperes, for an air conditioning unit for a dwelling unit. If 30-ampere fuses used as overcurrent protection will not carry the starting current of the unit, the rating of the fuses may be increased to a maximum value of _____.
40 amperes
18 amperes x 225 % = 40.5 amperes
The NEC requires branch circuits be rated in accordance with the overcurrent protective device. Therefore, which of the following combinations of loads are permitted for lighting branch-circuits?
a. 20, 30, 40, 50 and 70 amperes
b. 20, 30, 40, 50 and 60 amperes
c. 15, 25, 35, 45 and 50 amperes
d. 15, 20, 30, 40 and 50 amperes
d. 15, 20, 30, 40 and 50 amperes
Fill in the blank:
As a general rule, outside open conductors on insulators must be covered or insulated when they are within _____ of a building or structure, other than supporting poles or towers.
10 feet
