FREE TN-LLE Raceway and Box Fill Questions and Answers

Question 1

What is the maximum number of 12 AWG THHN conductors permitted in a 4" x 4" x 1-1/2" square metal box?

Accepted Answer

9

Answer

First, find the volume of the box in NEC Table 314.16(A), which is 21.0 cubic inches. Next, find the volume required per 12 AWG conductor in Table 314.16(B), which is 2.25 cubic inches. Divide the box volume by the conductor volume: 21.0 / 2.25 = 9.33. Since you cannot have a fraction of a conductor, the maximum number is 9.

Question 2

A metal device box contains one duplex receptacle, four 14 AWG current-carrying conductors, and one 14 AWG grounding conductor. What is the total volume allowance required for these components?

Accepted Answer

14.0 cu. in.

Answer

Per NEC 314.16(B), calculate the allowances: four 14 AWG conductors count as 4. All grounding conductors count as a single allowance (1). The duplex receptacle counts as a double allowance (2). The total is 4 + 1 + 2 = 7 allowances. The volume per 14 AWG conductor from Table 314.16(B) is 2.00 cu. in. Total volume is 7 x 2.00 = 14.0 cu. in.

Question 3

What is the maximum number of 10 AWG THHN conductors permitted in a 3/4" Electrical Metallic Tubing (EMT)?

Accepted Answer

16

Answer

This is a direct lookup in the NEC Annex C tables. Go to Table C.1 for EMT. Find the row for THHN conductor type and 10 AWG size, then move across to the column for 3/4" trade size conduit. The table indicates a maximum of 16 conductors.

Question 4

What is the minimum trade size of Schedule 40 PVC conduit required to enclose three 6 AWG THWN conductors and two 8 AWG THWN conductors?

Accepted Answer

1"

Answer

First, find the area of each conductor from Chapter 9, Table 5: 6 AWG THWN = 0.0507 sq. in. and 8 AWG THWN = 0.0366 sq. in. Calculate total area: (3 x 0.0507) + (2 x 0.0366) = 0.1521 + 0.0732 = 0.2253 sq. in. Using Chapter 9, Table 4 for PVC Sch 40 and the 40% fill column (for over 2 wires), a 3/4" conduit allows 0.213 sq. in. (too small) and a 1" conduit allows 0.346 sq. in. Therefore, 1" is the minimum size.

Question 5

A junction box has straight pulls of 3" Rigid Metal Conduit (RMC) entering and leaving. What is the minimum required length of the box?

Accepted Answer

24 inches

Answer

NEC 314.28(A)(1) for straight pulls requires the length of the box to be a minimum of eight times the trade diameter of the largest raceway. The calculation is 8 x 3 inches = 24 inches. The box must be at least 24 inches long.

TN LLE - Tennessee Limited Licensed Electrician Practice Test

TN LLE - Tennessee Limited Licensed Electrician Practice Test

FREE TN-LLE Raceway and Box Fill Questions and Answers