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I'm talking about something like this Type LB Conduit Body

enter image description here

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Most code states that the splice has to be accessible. It appears that device is designed specifically for that purpose. –  DA01 Dec 13 '13 at 16:22
    
It is not clear to me whether it is designed to permit splicing or to facilitate pulling wires around the corner. –  ThePopMachine Dec 13 '13 at 16:26
    
I agree with DA01. Looks accessible to me, and unless this is the main coming into the breaker, it should meet the requirements Tester101 mentions in his answer. –  John Gaughan Dec 14 '13 at 5:12
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2 Answers

Depends.

  • If the conductors are 6 AWG or smaller.
  • There is enough free space.
  • It's not a short radius conduit body.
  • The volume is durably and legibly marked by the manufacturer.

Only then can the conduit body contain splices.

In your specific case, I don't see the volume listed in the specifications section on the Home Depot page. So you'd have to check the fitting itself, to determine if the manufacturer has marked the volume. You didn't say what size wires you're pulling, so I can't answer that definitively. You also didn't mention the number of conductors, so it's impossible for me to do the fill calculations.

The Codez

National Electrical Code 2014

ARTICLE 314 Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures

II. Installation

314.16 Number of Conductors in Outlet, Device, and Junction Boxes, and Conduit Bodies. Boxes and conduit bodies shall be of an approved size to provide free space for all enclosed conductors. In no case shall the volume of the box, as calculated in 314.16(A), be less than the fill calculation as calculated in 314.16(B). The minimum volume for conduit bodies shall be as calculated in 314.16(C).

(C) Conduit Bodies.

(1) General. Conduit bodies enclosing 6 AWG conductors or smaller, other than short-radius conduit bodies as described in 314.16(C)(2), shall have a cross-sectional area not less than twice the cross-sectional area of the largest conduit or tubing to which they can be attached. The maximum number of conductors permitted shall be the maximum number permitted by Table 1 of Chapter 9 for the conduit or tubing to which it is attached.

(2) With Splices, Taps, or Devices. Only those conduit bodies that are durably and legibly marked by the manufacturer with their volume shall be permitted to contain splices, taps, or devices. The maximum number of conductors shall be calculated in accordance with 314.16(B). Conduit bodies shall be supported in a rigid and secure manner.

(3) Short radius conduit bodies. Conduit bodies such as capped elbows and service-entrance elbows that enclose conductors 6 AWG or smaller, and are only intended to enable the installation of the raceway and the contained conductors, shall not contain splices, taps, or devices and shall be of sufficient size to provide free space for all conductors enclosed in the conduit body.

Examples of short radius conduit bodies

Capped Elbow

Capped Elbow

Box Fill Calculation

For each current carrying conductor that terminates within the box, you'll add 1. So if you're pulling one ungrounded (hot) conductor, one grounded (neutral), and one grounding conductor. If you want to splice within the box, the calculation would look like this.

Ungrounded (hot)        1
Ungrounded (hot)        1
Grounded (neutral)      1
Grounded (neutral)      1
--------------------------
                        4

If grounding conductors are used, you'll add 1.

Current Carying         4
Grounding               1
--------------------------
                        5

Once you have the conductor count, you'll use Table 314.16(B) to determine the required volume.

Table 314.16(B)

NOTE: You'll always base the calculation off the largest conductor used. so if you have a #14 grounded (neutral) and a #12 ungrounded (hot), you'll use 2.25 because of the #12. If you're using grounding conductors that are a different size than the current carrying conductors, you'll multiply them separately (#12 hot, #12 neutral, #14 ground = 2 x 2.25 + 1 x 2.00).

14 AWG

If the largest conductor used is 14 AWG, you'll multiply the conductor count by 2.00 according to Table 314.16(B).

`5 * 2.00 = 10.00'

Which means the box must have a volume of at least 10 cubic inches, if you want to splice within it.

12 AWG

If the largest conductor used is 12 AWG, you'll multiply the conductor count by 2.25.

5 * 2.25 = 11.25

So in this case, the box must have a volume of at least 11.25 cubic inches.

3 Ungrounded (hot) Conductors

If you were pulling 3 ungrounded (hot) conductors, the calculations would look like this.

Ungrounded (hot)        1
Ungrounded (hot)        1
Ungrounded (hot)        1
Ungrounded (hot)        1
Grounded (neutral)      1
Grounded (neutral)      1
Grounding               1
--------------------------
                        7

14 AWG

7 * 2.00 = 14 cubic inches

12 AWG

7 * 2.25 = 15.75 cubic inches

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Thanks. For purpose of this question, assume it is just a cable-to-cable splice of 12-2 or 12-3 Type NM. –  ThePopMachine Dec 13 '13 at 17:09
    
@ThePopMachine Does the fitting have a volume marked on it, and if so, what is it? –  Tester101 Dec 13 '13 at 17:10
    
From what I recall, there is a volume marked (molded) on the inside of these. –  Ecnerwal Dec 13 '13 at 17:18
    
For Carlon: 1/2" 4.0 c.i., 3/4 12.0 c.i., 1" 12.0 c.i. - HD's specs page is useless, but Carlon publishes the data. –  Ecnerwal Dec 13 '13 at 17:25
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12-2 will work, 12-3 is too much.

If you are using a 3/4" Carlon, it's 12 cubic inches and should be marked. 12-2 with ground, spliced, needs 5X 2.25", 11.25 cubic inches, passes. 5 is two neutrals and two hots that terminate in the box, plus one for the ground. 12-3 with ground needs 7X 2.25, 15.75 cubic inches, fails (unless you increase to a 1-1/4" LB with 32 cubic inch volume).

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