Using Wire Tables

What is the ampacity of a No. 3-AWG XHHW in a wet location at 30 degrees C? There are not more than three conductors in the conduit. a. 85 b. 100 c. 110 d. 95

b. 100 Because of the wet location, Table 310.104(A) shows the 75 Degree column of Table 310.15(B)(16) for ampacity. 30 degrees C shows no correction factor is needed for temperature.

What's the ampacity of each 1/0 THHN conductor when there are four current-carrying conductors installed in a raceway in a dry location? a. 111A b. 136A c. 153A d. 171A

b. 136A 1/0 THHN at 90°C = 170A [Table 310.15(B)(16)] Ampacity = Table Ampacity x Adjustment Factor of 80% [Table 310.15(B)(3)(a)] Ampacity = 170A x 0.80 = 136A

What is the maximum overcurrent protection for a 6-AWG THW feeder in an ambient temperature of 30° C? a. 50 amp b. 60 amp c. 70 amp d. 80 amp

c. 70 amp Table 310.15(B)(16) shows 65 amps. 240.4(B) shows the next standard size, which is 70 amps.

Conductor sizes are expressed in American Wire Gage (AWG) from 40 AWG through 4/0 AWG. Conductors larger than _____ are expressed in circular mils. a. 1 AWG b. 1/0 AWG c. 3/0 AWG d. 4/0 AWG

d. 4/0 AWG [110.6 and Table 310.16]

What's the ampacity of an 8 THHN conductor when installed in a walk-in cooler (dry location) if the ambient temperature is 50°F? a. 40A b. 50A c. 55A d. 63A

d. 63A 55A x 1.15 (Temperature Correction Factor from Table 310.15(B)(2)(a)) = 63.25A [Table 310.15(B)(16)]. Note: Ampacity increases if the ambient temperature is less than 78°F.

What is the ampacity of a 8-AWG THWN copper conductor in an ambient temperature of 115° F? The conduit contains no more than three conductors. a. 37.5 amps b. 50 amps c. 45.1 amps d. 55 amps

a. 37.5 amps 50 x .75 = 37.5 amps Note that temperature in Celsius is on the left, and in Fahrenheit on the right of the temperature adjustment table.

What is the derating factor, if any, for thirty-five conductors in a 25" conduit nipple? a. 45% b. 40% c. 70% d. 0%

b. 40% Table 310.15(B)(3)(a) A conduit nipple is 24 inches or less.

A single-phase load after demand factors have been calculated is 286 amperes at 240/120 volts, and requires two phase conductors and a neutral. The ungrounded conductors are paralleled (two to each set) in one conduit. What size THW conductors are required to meet NEC requirements? a. 1/0 b. 2/0 c. 3/0 d. 4/0

c. 3/0 286 amps / 2 = 143 amps on each conductor. (This means that two conductors tied together at each end serve as one parallel set capable of carrying 286 amps.) Table 310.15(B)(3)(a) shows an 80% derate. Divide by this factor to find the necessary ampacity for each conductor: 143 amps / .80 = 178.75 amp capacity is needed. In parallel and after derate, this gives us a capacity of 320 amps for each ungrounded set. (160 x 2 = 320)

What is the maximum ampacity for one 14-AWG THW conductor that is in a raceway with five other 12-AWG THW conductors? The conduit also contains two 14-AWG grounding conductors for a total of eight conductors in the raceway. a. 15 amps b. 20 amps c. 14 amps d. 16 amps

d. 16 amps Do not count the grounding conductors Table 310.15(B)(3)(a) 20 amps x 80% = 16 amps

1/0 THHN at 90°C = 170A [Table 310.15(B)(16)] Ampacity = Table Ampacity x Adjustment Factor of 80% [Table 310.15(B)(3)(a)] Ampacity = 170A x 0.80 = 136A a. 21A b. 25A c. 32A d. 40A

b. 25A Ampacity = Ampacity x Temperature Correction x Bundle Adjustment [Table 310.15(B)(2)(a), Table 310.15(B)(3)(a) and Table 310.15(B)(16)] Temperature Correction = 0.91 Bundle Adjustment = 0.70 Ampacity = 40A x 0.91 x 0.70 = 25.48A

What's the minimum size THHN conductor that's permitted to terminate on a 50A circuit breaker or fuse if the circuit breaker and equipment terminals are listed for 75°C conductor sizing? a. 10 AWG b. 8 AWG c. 6 AWG d. 4 AWG

b. 8 AWG This requires an 8 AWG conductor, rated 50A at 75°C in accordance with Table 310.15(B)(16).

Three electric heaters have a line current of 35 amperes each. Each heater is connected to one phase and a grounded conductor. The six conductors are required to be what size THHN? a. No. 10 b. No. 8 c. No. 6 d. No. 4

b. No. 8 35 x 125 % [424.3(B)] = 43.75 amps 43.75 amps / .80 [Table 310.15(B)(3)(a)] = 54.69 amps Note: Divide by 80% in order to increase to the needed conductor ampacity that is to be derated. Derate from the temperature column of the insulation type, go to the 90 degree column of Table 310.15(B)(16) and find that No. 8 THHN is good for 55 amps. Do the calculation in reverse by derating the wire, it is 55 amps x .80 = 44 amps. The continuous load is 43.75 amps.

What is the maximum ampacity for 2-AWG RHH conductors? They feed a load operating in a poorly ventilated area where the ambient temperature is 32° C. a. 118.3 amps b. 122.6 amps c. 188.9 amps d. 124.8 amps

d. 124.8 amps 130 x .96 = 124.8 amps

What is the maximum ampacity of a 8-AWG THHN conductor in an ambient temperature of 30° C? There are six conductors in the raceway. a. 55 amps b. 52 amps c. 40 amps d. 44 amps

d. 44 amps Derate from the 90 degree column. 55 x 80% = 44 amps

What is the ampacity of a 12-AWG THHN conductor in an ambient temperature of 70° F? a. 30 amps b. 31.2 amps c. 25 amps d. 28.4 amps

b. 31.2 amps Table 310.15(B)(16) and Correction Factors in Table 310.15(B)(2)(a). Adjust from the 90 degree column because of the insulation type. 30 amps x 1.04 = 31.2 amps. Use the 60 degree or the 75 degree column for conductor ampacity if the termination temperature ratings are not rated to the higher temperature of 90 degrees. Derate from the column under the insulation type.

What size conductor is required for a 70A breaker that supplies a 70A noncontinuous load where the terminals are rated 75°C? a. 8 AWG b. 6 AWG c. 4 AWG d. any of these

c. 4 AWG [210.20(A) and Table 310.15(B)(16)] Don't be tricked by the fictitious all of the above type answer.

What is the maximum ampacity for a 6-AWG THHN conductor in an ambient temperature of 42° C? a. 70.5 amps b. 53.3 amps c. 65.25 amps d. 75 amps

c. 65.25 amps 75 amps x .87 = 65.25 amps