Box and Conduit Fill Calculations

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Box & conduit Fill Calculations

Box and

Conduit Fill

Calculations

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Volume required per

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Conduit fill - Box sizing

Table 314.16(a) : Number of conductors in box 600v, nominal or less

CONDUCTORS:

1. Conductors originating outside box, terminating in box count as 1 conductor

2. Conductors originating outside box, spliced in box counts as 1 conductor

3. A conductor entering a box, spliced to a conductor leaving box counts as 2 conductors

4. Conductors passing through box without splices or terminations count as 1 conductor

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Conduit fill - Box sizing

2005 NEC Change

Looped conductors now count as 2

conductors

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EQUIPMENT GROUNDING CONDUCTOR:

1. One, two or more bare, insulated or covered system

grounding conductors all count the same size, count as 1

conductor

2. One, two or more bare, insulated or covered system grounding conductors of various sizes, count as one conductor based upon largest equipment grounding conductor

3. A separate ‘ISOLATED’ equipment grounding conductor counts as 1 conductor in addition to system grounding conductor. Count as size of ‘ISOLATED’ grounding conductor or largest if various sizes.

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CLAMPS:

1. Clamps installed inside box by factory count as 1 conductor

2. Clamps installed in box in the field count as 1 conductor (Conductor size based on largest conductor in box)

SUPPORT FITTINGS:

1. Fixture studs count as 1 conductor 2. Fixture hickeys count as 1 conductor

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DEVICE(S) IN BOX:

1. Yoke or strap with switch, counts as 2 conductors 2. Yoke or strap with duplex receptacle counts as 2

conductors

3. Yoke or strap with triplex receptacle counts as 2 conductors

4. Yoke or strap with switch & light on same yoke or strap counts as 2 conductors

5. Yoke with any combination of three devices on same yoke or strap counts as 2 conductors

(Conductor size based on LARGEST conductor connected to device or equipment)

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Yoke or Strap

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Conductor Counts for other than wire

Cable Clamps Fixture Stud Hickey NM 12-2 W/GRD

Fixture Stud = 1 Conductor Hickey = 1 Conductor Cable Clamps (2) = 1 Conductor Total Conductor Count = 3 Conductors

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Counting Devices

1 Yoke 1 Device 1 Conductor 1 Yoke 1 Device 1 Conductor 1 Yoke 2 Devices 1 Conductor 1 Yoke 3 Devices 1 Conductor

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Box & conduit Fill Calculations Through Box Terminate in Box All Conductors Terminate in Box Count 6 total Through Box 2 Terminate in Box 4

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Factory installed clamps

8

-

12

’

s & 1 clamp = 9

Factory or Field Installed Clamps

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EGC

EGC = Equipment Grounding Conductor

IEGC = Insolated Equipment Grounding Conductor BJ = Bonding Jumper BJ IEGC EGC = 1 IEGC = 2 BJ = 0 Total = 2

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Box & conduit Fill Calculations Octagonal / 4/0 Box 2 - #8 AWG 2 - #12 AWG 2 - #12 AWG

2 - #8 @3.00 Cu = 6 Cu in

Fix Stud @3.00 Cu in = 3 Cu in

4 - #12 @2.25 Cu in = 9 Cu in

Total = 18 Cu in

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#14 Bare EGC

#8 AWG

#12 AWG

#18 AWG fixture wire #10 AWG #18 = 1.5 cu in x 2 = 3.00 cu in #14 = 2.0 cu in x 1 = 2.00 cu in #12 = 2.25 cu in x 4 = 9.00 cu in #10 = 2.50 cu in x 2 = 5.00 cu in #8 = 3.00 cu in x 2 = 6.00 cu in Fix Stud = #8 = 3.00 cu in = 3.00 cu in

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Bad Planning

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314.16(b)(1) Exception

Canopy Cover

EGC Terminations in Canopy Cover To Fan To Fixture

4 - Smaller than #14 Fixture wires

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Counting with a device

2 - #8 AWG 2 - #12 AWG 2 - #12 AWG

2 - #8 @3.00 cu in = 6 cu in

4 - #12 @2.25 cu in = 9 cu in

Yoke @2.25 cu in = 4.5 cu in

Total Volume Required = 19.5 cu in

Largest conductor allowed = #10 NEC 110.14(A)

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Conduit Fill

Calculations

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Major Fraction Change

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What size EMT is needed for 3 - 2/0 AWG THW Cu

conductors and 4 - 4/0 AWG THHN Cu conductors ?

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Table 5 – Cross-Sectional Area of Individual Conductors

2/0 AWG THW Cu = .2624 X 3 = .7872 4/0 AWG THHN Cu = .3237 X 4 = 1.2984 Total Square Inches for Conductors = 2.0820

Table 4 – 40% fill column for “Over 2 wires”.

2.0820 Sq.In. Requires a 2 ½ inch EMT Conduit 40% fill for 2 ½ inch EMT = 2.343 Sq. In.

Answer = 2 ½ Inch EMT

What size EMT is needed for 3 - 2/0 AWG THW Cu

conductors and 4 - 4/0 AWG THHN Cu conductors ?

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What size IMC is required for 6 - 12 AWG RHH Cu

conductors without outer covering and 4 -14 AWG

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What size IMC is required for 6 - 12 AWG RHH Cu

conductors without outer covering and 4 -14 AWG

RHH Cu Conductors with outer covering ?

Table 5 – Cross-Sectional Area of Individual Conductors

14 AWG RHH Cu With Outer Covering = .0293 X 4 = .1172 12 AWG RHH Cu Without Outer Covering = .0260 X 6 = .1560 Total Square Inches for Conductors = .2732

Table 4 – 40% fill column for “Over 2 wires”.

.2732 Sq.In. Requires a 1 inch IMC Conduit 40% fill for 1 inch IMC = .384 Sq. In.

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Box & Conduit Fill Exam

10 Questions

30 Minutes

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Box fill Answers

1. (b) 10.75 cu in 314.16(b) 3 - #12’s @ 2.25 cu in = 6.75 cu in 2 - #14’s @ 2.00 cu in = 4.00 cu in 10.75 cu in 2. (b) 2 conductors 314.16 (b) 3. (b) 4 Table 314.16(a) 4. (d) 17.5 cu in Table 314.16(b) #10 = 2.5 cu in 7 - #10’s x 2.5 cu in = 17.5 cu in

5. (a) 0.0181 in2 _{Table 5 (note * notations by insulations)}

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Box & conduit Fill Calculations 6. (d) 39.75 cu in Table 314.16(b) #8 = 3.00 cu in #12 = 2.25 cu in Clamps - #8 = 3.00 cu in 7 - #8 @ 3.00 cu in = 21.00 cu in 1 - #8 @ 3.00 cu in = 3.00 cu in 7 - #12 @ 2.25 cu in = 15.75 cu in 39.75 cu in

Box fill Answers

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3 - #8 ungrounded conductors count as 3 {314.16(b)(1)} 3 - #8 grounded conductors count as 3 {314.16(b)(1)} 3 - #8 grounding conductors count as 1 {314.16(b)(5)}

4 - clamps count as 1 {314.16(b)(2)}

3 - #12 ungrounded conductors count as 3 {314.16(b)(1)} 3 - #12 grounded conductors count as 3 {314.16(b)(1)} 3 - #12 grounding conductors count as 1 {314.16(b)(5)}

#8 conductors 7 - #8 @ 3.00 cu in = 21.00 cu in Clamps 1 - #8 @ 3.00 cu in = 3.00 cu in #12 conductors 7 - #12 @ 2.25 cu in = 15.75 cu in 39.75 cu in

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7. (b) 2.2831 in² T.5

8. (b) 1 1/4” IMC T.4

9. (a) .384in² T.4