Unit 9: Multi Family Dwelling Service Calculations Flashcards
Determine NEC-compliant service loads, analyze demand factors, and differentiate between standard and optional methods.
Fill in the blank:
When calculating the service entrance conductors for a farm service, the second largest load of the total load, shall be computed at ________.
75%
According to the NEC®, what alteration is permitted if multiple grounding connections of driven ground rods result in objectionable current?
Discontinue one or more grounding connections.
Fill in the blank:
Installation of information technology equipment remote disconnecting controls shall not be required for critical operations data systems when several conditions are in place including ________.
an approved fire suppression system suitable for the application is in place
What is the term used for electrical equipment or materials to which a symbol has been attached, or other identifying mark of an organization that is acceptable to the authority having jurisdiction?
labeled
Fill in the blank:
Rooms or areas of dwelling units shall be protected by a listed arc-fault circuit interrupter (AFCI), combination type, installed to provide protection of the ________
entire branch circuit
Fill in the blank:
All receptacles located within at LEAST ________ of a therapeutic tub shall be provided with GFCI protection.
6 feet
Fill in the blank:
When applying the general method of calculations for a dwelling unit having four (4) or more fastened in place appliances, other than electric ranges, dryers, space heating equipment, or airconditioning equipment, it shall be permissible to apply a demand factor of ________ when sizing the service conductors.
75%
Fill in the blank:
Branch circuits that supply electric signs shall be considered ________ loads for the purposes of calculations.
continuous
Fill in the blank:
Additional services shall be permitted for a single building or other structure sufficiently large to make two (2) or more services necessary if permitted by ________.
special permission by the local authority having jurisdiction
What is the requirement for transformers serving electric discharge lighting with a rating of more than 1,000 volts?
The transformers should be installed as near to the lamps as practicable.
Assuming the use of THWN copper conductors and terminations rated for 75°C, determine the MINIMUM feeder conductor size when given the following related information:
- 120-volt, single-phase system
- one (1) 30 ampere continuous load
- one (1) 5 ampere non-continuous load
8 AWG
30 amp continuous load x 125% = 37.5 amperes
5 amp non-continuous load x 100% = 5.0 amperes
Total load = 42.5 amperes
Size 8 AWG THWN CU conductors with an ampacity of 50
amperes should be selected from Table 310.16.
Fill in the blank:
As a general rule, all conductors of a multiwire branch circuit shall originate from the same panelboard, simultaneously disconnect all ungrounded conductors and supply only line-to- ________ loads.
neutral
Fill in the blank:
In general, for newly installed grounded systems, where branch circuits or feeders supply separate buildings or structures, equipment grounding conductors are ________.
required
Given: An underground run of PVC conduit with size 4 AWG conductors is the wiring method used to supply an air-conditioning unit that is protected by an overcurrent protective device rated 60 amperes. What is the MINIMUM size wire-type copper equipment grounding conductor that must be installed in the PVC?
10 AWG
Fill in the blank:
Service conductors installed as open conductors or multi conductor cable without an overall outer jacket shall have a horizontal clearance of not less than ________from windows that are designed to be open, doors, porches, ladders, stairs or similar locations.
3 feet
Fill in the blank:
Utilization equipment weighing not more than 6 pounds is permitted to be supported to any box or plaster ring secured to a box, provided the equipment or its supporting yoke is secured with at LEAST two (2) ________ or larger screws.
No. 6
Fill in the blank:
Photovoltaic systems operating at ________ dc or greater between any two conductors shall be protected by a listed PV arc-fault circuit interrupter or other system components listed to provide equivalent protection.
80 volts
Fill in the blank:
In general, for household electric ranges with a rating of 8¾ kW or more, the MINIMUM branch-circuit rating shall be ________.
40 amperes
Fill in the blank:
Each doorway leading into a transformer vault from the building interior shall be provided with a tight-fitting door that has a minimum fire rating of three (3) hours. However, if the transformer vault is protected with an automatic sprinkler system, the construction rating of ________ shall be permitted.
1 hour
Fill in the blank:
Where a 240-volt, single-phase, 5 kW storage-type water heater is located in the basement of a dwelling, and the load-center panel board is located outdoors and not capable to be locked in the open position, a disconnect in the basement for the water heater is ________.
required
What is the MAXIMUM ampere rating permitted for a 125-volt, single-phase, receptacle outlet having a cord-and plug connected motor load that does not have individual overload protection?
15 amperes
Fill in the blank:
After all demand factors have been taken into consideration and calculations completed, a one family dwelling with a 120/240-volt, single-phase electrical system has a demand load of 35,000 VA. The MINIMUM size THWN copper ungrounded (line) conductors required for an underground installed service lateral is ________.
2 AWG
I = 36,000 VA/ 240 volts = 145.8 amperes x .83 = 121 amperes
Size 2 AWG THWN CU conductors with an ampacity of 125
amperes should
be selected from Table 310.12.
What is permitted in the dedicated electrical space above a switchboard or panelboard?
leak protection apparatus
Which 3-phase system is allowed to be a high-impedance grounded neutral system, where a resistor limits the ground-fault current to a low value?
480-volts
