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.
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:
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 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
100 amperes x 125% = 125 amperes
Fill in the blank:
For the purpose of maintaining and servicing a 3-phase, 208Y/120-volt switchboard, a MINIMUM clear working depth distance of ________ must be maintained in front of the switchboard.
3 feet
Fill in the blank:
When a permanently installed generator is set up 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
Fill in the blank:
For a direct burial feeder cable to a water well pump 50 feet from a dwelling, the NEC® approves ________ for use.
Type UF cable
True or false:
All of the following wiring methods are permitted in a ceiling space used as a return-air plenum EXCEPT rigid PVC conduit.
TRUE
Fill in the blank:
A 240-volt, single-phase 10 kW commercial dishwasher will draw ________ of current.
42 amperes
I = 10,000 watts/240 volts
= 41.6 amperes
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
True or false:
All wiring methods are permitted in a ceiling space used as a return-air plenum EXCEPT Type SOW.
TRUE
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:
The MINIMUM number of 120-volt, 15-ampere, general lighting branch circuits required for a dwelling with 70 feet by 30 feet of livable 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)/1800 VA (circuit) = 3.5 = 4 general lighting circuits
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 on 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
Fill in the blank:
According to the NEC®, lighting branch circuits must be rated based on the overcurrent protective device. The permitted load ratings for these circuits are ________.
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
