Electrician Training Electrical Certification
»NEW eBOOK«
wiring recessed light fixtures Electrical Wiring Electrical Troubleshooting and Electrical Repairs wire outdoor light fixture Home Electrical Wiring Diagrams

wiring home generator and transfer switch wiring a 220 volt range cord outlet Wiring for GFCI Outlets Wiring Outlets and a Switched Outlet Wiring and Installing Ceiling Fans and Remote Controls wire dimmer switch wiring diagrams for switches wiring a dryer cord and 220 outlet circuit breaker panel
Electrical Wire and Cable
ask the electrician
Electrician Training Electrical Certification wiring recessed light fixtures Electrical Wiring Electrical Troubleshooting and Electrical Repairs wire outdoor light fixture Home Electrical Wiring Diagrams
wiring home generator and transfer switch wiring a 220 volt range cord outlet Wiring for GFCI Outlets Wiring Outlets and a Switched Outlet Wiring and Installing Ceiling Fans and Remote Controls wire dimmer switch wiring diagrams for switches wiring a dryer cord and 220 outlet circuit breaker panel
Electrical Wire and Cable

Electrical Code for Electrical Box Fill Capacity

electrical-box-wiring Summary: One of the mistakes often made is over loading an electrical box with too many wires. This will cause switches and outlets to not fit correctly and could even cause wires to become damaged. This information will help you plan your electrical box size properly.

The Minimum Size Junction Box for Electrical Wiring


Home Electrical Wiring Tips

Helping You Wire it Right
Check out my YouTube Channel, and Subscribe!

Part (1) of Section 370-16(a) describes in detail the method of counting wires, as well as clamps, fittings, or devices (i.e., switches, receptacles, combination devices) - by establishing an equivalent conductor-value for each.

These values are added together to get a total number of conductors.

The minimum size box is the smallest one in the Box Fill Table (shown) that can accommodate that number of conductors.

BOX FILL TABLE
DEDUCTIONS 6 7 8 9 10 11 12 13 14
Volume Required per Conductor Size per Deductions #18
(1.50)
9.00 10.50 12.00 13.50 15.00 16.50 18.00 19.50 21.00
#16
(1.75)
10.50 12.25 14.00 15.75 17.50 19.25 21.00 22.75 24.50
#14
(2.00)
12.00 14.00 16.00 18.00 20.00 22.00 24.00 26.00 28.00
#12
(2.25)
13.50 15.75
18.00 20.25 22.50 24.75 27.00 29.25 31.50
#10
(2.50)
15.00 17.50 20.00 22.50 25.00 27.50 30.00 32.50 35.00
#8
(3.00)
18.00 21.00 24.00 27.00 30.00 33.00 36.00 39.00 42.00
#6
(5.00)
30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00

Check Out What Others Are Sharing at Ask the Electrician:
Much appreciated. We hack of all trades need a little help occasionally. Phil from Ann Arbor , Michigan

Electrical Box Fill Table Information


Box Fill Guidelines:

  • No matter how many ground wires, they only count as one conductor in the box.
  • A wire running through the box counts as one wire.
  • Each wire coming into a splice connector is counted as one wire.
  • Each wire connecting to a device counts as one wire of that size.
  • When devices are mounted in the box, the total conductor count must be increased by two for each mounting strap.

NEC Table 370-16 Electrical Box Fill



NEC Table 370-16(a) for Metal Boxes


Number of Conductors in Outlet, Device,
and Junction Boxes

Box Dimension
in Inches
Trade Size
or Type

Minimum
Capacity
(in.3)

Maximum Number of Conductors

No. 18

No. 16

No. 14

No. 12

No. 10

No. 8

No. 6

4 X 1-1/4 round or octagonal
4 X 1-1/2 round or octagonal
4 X 2-1/8 round or octagonal

12.5
15.5
21.5

8
10
14

7
8
12

6
7
10

5
6
9

5
6
8

4
5
7

2
3
4

4 X 1-1/4 square
4 X 1-1/2 square
4 X 2-1/8 square

18.0
21.0
30.3

12
14
20

10
12
17

9
10
15

8
9
13

7
8
12

6
7
10

3
4
6

4-11/16 X 1-1/4 square
4-11/16 X 1-1/2 square
4-11/16 X 2-1/8 square

25.5
29.5
42.0

17
19
28

14
16
24

12
14
21

11
13
18

10
11
16

8
9
14

5
5
8

3 X 2 X 1-1/2 device
3 X 2 X 2 device
3 X 2 X 2-1/4 device
3 X 2 X 2-1/2 device
3 X 2 X 2-3/4 device
3 X 2 X 3-1/2 device

7.5
10.0
10.5
12.5
14.0
18.0

5
6
7
8
9
12

4
5
6
7
8
10

3
5
5
6
7
9

3
4
4
5
6
8

3
4
4
5
5
7

2
3
3
4
4
6

1
2
2
2
2
3

4 X 2-1/8 X 1-1/2 device
4 X 2-1/8 X 1-7/8 device
4 X 2-1/8 X 2-1/8 device

10.3
13.0
14.5

6
8
9

5
7
8

5
6
7

4
5
6

4
5
5

3
4
4

2
2
2

3-3/4 X 2 X 2-1/2 masonry
  box / gang
3-3/4 X 2 X 3-1/2 masonry
  box / gang

14.0

21.0

9

14

8

12

7

10

6

9

5

8

4

7

2

4


Electrical Wiring Tips for Home Electrical Wiring Projects

Tripping Circuit Breaker, Outlet at a Wall Switch, Light Fixture without a Ground Wire, Help with Home Electrical Wiring Projects.

See more House Wiring Videos from Ask The Electrician:

Home Electrical Wiring Videos


Learn more with my Home Electrical Video Course:

Basic Home Electrical Wiring by Example


» You Can Avoid Costly Mistakes! «

Here is How to Do It:
Wire It Right with the help of my Illustrated Wiring Book

Great for any Home Wiring Project.


  electrical wiring  

Complete Guide to Home Electrical Wiring

Perfect for Homeowners, Students,
Handyman, Handywomen, and Electricians
Includes:
Wiring GFCI Outlets
Wiring Home Electric Circuits
120 Volt and 240 Volt Outlet Circuits
Wiring Light Switches
Wiring 3-Wire and 4-Wire Electric Range
Wiring 3-Wire and 4-Wire Dryer Cord and Dryer Outlet
How to Troubleshoot and Repair Electrical Wiring
Wiring Methods for Upgrading Electrical Wiring
NEC Codes for Home Electrical Wiring
....and much more.