Unit 4: Conductor Ampacity and Sizing Flashcards
Understanding NEC® tables and guidelines to determine the correct conductor size based on ampacity, temperature rating, insulation type, and adjustment factors for safe electrical installations.
Fill in the blank:
Conductors installed in electrically heated floors in bathrooms, kitchens, and in hydromassage bathtub locations shall be provided with ________ protection.
ground-fault circuit interrupter (GFCI)
Fill in the blank:
Where large electrical equipment containing overcurrent devices, rated at LEAST ________ or more, is installed in an equipment room, personnel door(s) located less than 25 feet from the nearest edge of the working space must open in the direction of egress and have listed panic hardware.
800 amperes
What is the MAXIMUM length of a flexible cord that may be used for a recirculating water-pump motor on a swimming pool at a dwelling
3 feet
Fill in the blank:
Plate grounding electrodes shall be installed NOT less than ________ below the surface of the earth.
30 inches
Fill in the blank:
A disconnecting means shall be provided on the supply side of all fuses in circuits having a voltage of at LEAST ________ to ground so that each circuit containing fuses can be independently disconnected from the source of power.
150 volts
Where an 80-ampere, 240-volt, single-phase load is located 200 feet from a panelboard and is supplied with size 3 AWG copper conductors with THWN insulation, what is the approximate voltage-drop on the circuit? (K = 12.9)?
7.84 volts
VD = (2KID VD)/CM = (2 x 12.9 x 80 amps x 200 ft.)/52,620 CM = 7.84 volts
Fill in the blank:
Enclosures in a Class I, Division 1 location containing components that have arcing devices must have an approved conduit seal located within at LEAST ________ of each conduit run entering or leaving such enclosures.
18 inches
Fill in the blank:
The purpose of the NEC® is ________.
the practical safeguarding of persons and property
Fill in the blank:
The NEC® considers the area around the outdoor motor fuel dispensing pumps of an automotive service station to be a hazardous location. This area extends a height of 18 inches above grade, and up to a horizontal distance of ________ from the enclosure of the outdoor motor fuel dispensing pumps.
20 feet
According to the National Electrical Code®, what are the three (3) separate branches of the essential electrical systems for hospitals?
- Life safety branch
- Equipment branch
- Critical branch
Fill in the blank:
Type UF cable is NOT permitted to be used ________.
as service-entrance cable
Where an office building has a 208Y/120-volt, 3-phase service with a balanced net computed load of 90 kVA, what is the current each ungrounded (phase) conductor will carry at full load?
250 amperes
I = (kVA x 1,000)/E x 1.732
I = (90 x 1,000)/208 x 1.732
= 90,000/360.25 = 250 amperes
When bonding the structural reinforcing steel of a swimming pool, what is the smallest size wire-type solid bare copper bonding conductor permitted for this installation?
8 AWG
Fill in the blank:
For dwelling units, GFCI protection shall be provided for lighting outlets not exceeding 120 volts where installed in ________.
I. crawl spaces
II. bathrooms
I only
Fill in the blank:
Where a motor of more than 1 horsepower has a temperature rise of 50 deg. C indicated on the nameplate, for the purposes of selecting the overload device, this device shall be selected to trip at NO more than ________ of the motor’s full-load ampere rating. (Assume modification of this value is not necessary.)
115 percent
Fill in the blank:
Where a size 14 AWG branch-circuit conductor protected by a 15 ampere rated circuit breaker supplies three (3) 20 ampere rated duplex receptacles, this branch circuit ________.
is not in compliance with the NEC® because the receptacles have a 20 ampere rating
What is the MAXIMUM number of times a wire-type grounding electrode conductor is permitted to be spliced by use of listed split-bolt connectors?
none
Given: A metal junction box has a volume of 27 cubic inches and contains a total of six (6) size 12 AWG conductors, no grounding conductors, devices or fittings are contained in the box. Additional wires of size 10 AWG need to be added in the box. What is the MAXIMUM number of size 10 AWG conductors may be added to this box?
Five
Size 12 AWG = 2.25 cu. in. x 6 (existing wire in box) = 13.5 cu. in.
27.0 cu. in. (allowable fill of box)
-13.5 cu. in. (existing wire in box)
13.5 cu. in. (remaining space available)
13.5 cu. in. (remaining space) = 5.4 = 5 size 10 AWG wires may be added =
2.5 cu. in. (#10)
For enclosing a mobile home supply cord, what is the MAXIMUM trade size conduit permitted between the branch circuit panelboard of a mobile home and the underside of a mobile home floor?
1 1⁄4 in.
For fixed wiring in an area above Class I locations in a commercial repair garage, what acceptable wiring methods are approved by NEC®?
- Type MI cable
- Type TC cable
- Type MC cable
Fill in the blank:
Class II locations are those that are hazardous because of the presence of ________.
Combustible dust
Fill in the blank:
Branch-circuit conductors supplying a fixed storage-type electric water heater with a capacity of 120 gallons or less, shall have an ampacity of NOT less than ________ of the full-load current of the water heater.
125 percent
Fill in the blank:
Household-type appliances with surface heating elements having a MAXIMUM demand of more than ________ shall have its power supply subdivided into two (2) or more circuits.
60 amperes
Fill in the blank:
When driving a ground rod and solid rock is encountered, the ground rod is permitted to be buried in a trench at LEAST ________ deep.
30 inches
