Raceways and Boxes Flashcards

An electrician is installing a run of 1/2-inch Electrical Metallic Tubing (EMT) on the surface of a wall. According to NEC Article 358, what is the maximum permitted spacing between supports for this raceway?

Answer: 10 feet

NEC 358.30(A) states that EMT shall be securely fastened in place at least every 3 m (10 ft). Additionally, a support is required within 3 feet of each termination point like a box or conduit body.

An electrician installs a junction box with raceways containing 4 AWG conductors entering and leaving on opposite walls for a straight pull. According to NEC 314.28(A)(1), what is the minimum required length of this pull box?

Answer: Eight times the trade size of the largest raceway.

NEC 314.28(A)(1) specifies that for straight pulls involving conductors 4 AWG or larger, the length of the box must be at least eight times the trade size (diameter) of the largest raceway entering the box.

What is the maximum total degrees of bends permitted in a single run of conduit between two pull points (e.g., from one junction box to another)?

Answer: 360 degrees

NEC articles for most raceway types, such as 344.26 for RMC and 358.26 for EMT, state that there shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points. This rule prevents damage to conductor insulation during pulling.

An electrician is calculating the required size of a device box that will contain one duplex receptacle, two 12/2 non-metallic sheathed cables, and has no internal clamps. How many conductor volumes must be counted for the duplex receptacle itself?

Answer: Two, based on the largest conductor connected to it.

According to NEC 314.16(B)(4), each yoke or strap containing one or more devices (like a switch or receptacle) requires a double volume allowance based on the size of the largest conductor connected to the device.

When installing more than two current-carrying conductors in a single raceway, what is the maximum allowable percentage of the raceway's interior cross-sectional area that can be filled?

Answer: 40%

NEC Chapter 9, Table 1 specifies the allowable fill percentages for raceways. For one conductor, the limit is 53%; for two conductors, it's 31%; and for more than two conductors, the maximum fill is 40%.

An electrician is installing a 4" x 4" x 1-1/2" square metal box. The box will contain four 12 AWG conductors and two 14 AWG conductors, all spliced within the box. There are no devices or internal clamps. Is this installation compliant with NEC box fill requirements?

Answer: No, the required volume exceeds the box's capacity.

First, find the box volume from NEC Table 314.16(A): a 4" x 1-1/2" square box has a volume of 21.0 cubic inches. Next, calculate the required volume using Table 314.16(B): four 12 AWG conductors require 4 x 2.25 = 9.0 cu. in., and two 14 AWG conductors require 2 x 2.0 = 4.0 cu. in. The total required volume is 9.0 + 4.0 = 13.0 cubic inches. Wait, let me re-verify that. The question asks if it is compliant. My calculation showed 13.0 cu. in. required and 21.0 cu. in. available, which would make it compliant. Let me re-read the question and my logic. Ah, I see, I should create a question where it is NOT compliant to make it a better test question. Let's adjust the conductor count. Let's try: six 12 AWG and four 14 AWG. Calculation: (6 * 2.25) + (4 * 2.0) = 13.5 + 8.0 = 21.5 cu. in. This exceeds the 21.0 cu. in. capacity. Perfect. Explanation: Per NEC Table 314.16(A), a 4" x 4" x 1-1/2" square box has a volume of 21.0 cubic inches. The required volume is calculated using Table 314.16(B): six 12 AWG conductors require 6 x 2.25 = 13.5 cu. in., and four 14 AWG conductors require 4 x 2.0 = 8.0 cu. in. The total required volume is 13.5 + 8.0 = 21.5 cubic inches. Since 21.5 cu. in. is greater than the 21.0 cu. in. capacity of the box, the installation is a violation.