#National Electrical Code 2014 ##Chapter 3 Wiring Methods and Materials ###Article 334 Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS ###II. Installation 334.15 Exposed Work.

 

(B) Protection from Physical Damage. Cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, or other approved means...

#National Electrical Code 2014 ##Chapter 9 Tables Notes to Tables

 

(5) For conductors not included in Chapter 9, such as multiconductor cables and optical fiber cables, the actual dimensions shall be used.

 

(9) A multiconductor cable or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.

#Calculate area of NM cable You should be able to find a spec sheet from the manufacturer of the cable you choose. I found the spec sheet for Southwire’s Romex® SIMpull ® Type NM-B, which lists the sizes of various cables. It lists 6/3 cable as having a diameter of 650 mils, or 0.650". From which you can calculate the cross-sectional area, using the formula πr².

#Conduit Fill Once you know the area of the cable, you can use Table 4 from Chapter 9 of the National Electrical Code to determine the size of conduit needed. Remember because of Note 9, you can use the 1 wire column (53%).

###Electrical Metallic Tubing (EMT) 1/2" @ 53% fill = 0.161 in.²
3/4" @ 53% fill = 0.283 in.²
1" @ 53% fill = 0.458 in.²

###Intermediate Metal Conduit (IMC) 1/2" @ 53% fill = 0.181 in.²
3/4" @ 53% fill = 0.311 in.²
1" @ 53% fill = 0.508 in.²

###Rigid Metal Conduit (RMC) 1/2" @ 53% fill = 0.166 in.²
3/4" @ 53% fill = 0.291 in.²
1" @ 53% fill = 0.470 in.²

###Rigid PVC Conduit (PVC), Schedule 80 1/2" @ 53% fill = 0.115 in.²
3/4" @ 53% fill = 0.217 in.²
1" @ 53% fill = 0.365 in.²

#National Electrical Code 2014 ##Chapter 9 Tables Notes to Tables

 

(8) Where bare conductors are permitted by other sections of this Code, the dimensions for bare conductors in Table 8 shall be permitted.

National Electrical Code 2014

Chapter 3 Wiring Methods and Materials

Article 334 Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS

II. Installation

334.15 Exposed Work.

(B) Protection from Physical Damage. Cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, or other approved means...

National Electrical Code 2014

Chapter 9 Tables

Notes to Tables

(5) For conductors not included in Chapter 9, such as multiconductor cables and optical fiber cables, the actual dimensions shall be used.

(9) A multiconductor cable or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.

Calculate area of NM cable

You should be able to find a spec sheet from the manufacturer of the cable you choose. I found the spec sheet for Southwire’s Romex® SIMpull ® Type NM-B, which lists the sizes of various cables. It lists 6/3 cable as having a diameter of 650 mils, or 0.650". From which you can calculate the cross-sectional area, using the formula πr².

Conduit Fill

Once you know the area of the cable, you can use Table 4 from Chapter 9 of the National Electrical Code to determine the size of conduit needed. Remember because of Note 9, you can use the 1 wire column (53%).

Electrical Metallic Tubing (EMT)

1/2" @ 53% fill = 0.161 in.²
3/4" @ 53% fill = 0.283 in.²
1" @ 53% fill = 0.458 in.²

Intermediate Metal Conduit (IMC)

1/2" @ 53% fill = 0.181 in.²
3/4" @ 53% fill = 0.311 in.²
1" @ 53% fill = 0.508 in.²

Rigid Metal Conduit (RMC)

1/2" @ 53% fill = 0.166 in.²
3/4" @ 53% fill = 0.291 in.²
1" @ 53% fill = 0.470 in.²

Rigid PVC Conduit (PVC), Schedule 80

1/2" @ 53% fill = 0.115 in.²
3/4" @ 53% fill = 0.217 in.²
1" @ 53% fill = 0.365 in.²

National Electrical Code 2014

Chapter 9 Tables

Notes to Tables

(8) Where bare conductors are permitted by other sections of this Code, the dimensions for bare conductors in Table 8 shall be permitted.

###Electrical Metallic Tubing (EMT) 1" @ 53% fill = 0.458 in.²

###Intermediate Metal Conduit (IMC) 1" @ 53% fill = 0.508 in.²

###Rigid Metal Conduit (RMC) 1" @ 53% fill = 0.470 in.²

###Rigid PVC Conduit (PVC), Schedule 80 1" @ 53% fill = 0.365 in.²

In this example, you'd need 1" conduit to fit the 6/3 nonmetallic sheathed cable.

Which means you'll be able to use 3/4" conduit, instead of 1".

###Electrical Metallic Tubing (EMT) 1/2" @ 53% fill = 0.161 in.²
3/4" @ 53% fill = 0.283 in.²
1" @ 53% fill = 0.458 in.²

1/2" @ 40% fill = 0.122 in.²
3/4" @ 40% fill = 0.213 in.²
1" @ 40% fill = 0.346 in.²

###Intermediate Metal Conduit (IMC) 1/2" @ 53% fill = 0.181 in.²
3/4" @ 53% fill = 0.311 in.²
1" @ 53% fill = 0.508 in.²

1/2" @ 40% fill = 0.137 in.²
3/4" @ 40% fill = 0.235 in.²
1" @ 40% fill = 0.384 in.²

###Rigid Metal Conduit (RMC) 1/2" @ 53% fill = 0.166 in.²
3/4" @ 53% fill = 0.291 in.²
1" @ 53% fill = 0.470 in.²

1/2" @ 40% fill = 0.125 in.²
3/4" @ 40% fill = 0.220 in.²
1" @ 40% fill = 0.355 in.²

###Rigid PVC Conduit (PVC), Schedule 80 1/2" @ 53% fill = 0.115 in.²
3/4" @ 53% fill = 0.217 in.²
1" @ 53% fill = 0.365 in.²

1/2" @ 40% fill = 0.087 in.²
3/4" @ 40% fill = 0.164 in.²
1" @ 40% fill = 0.275 in.²

In this example, you'd need 1" conduit to fit the 6/3 nonmetallic sheathed cable.

Since there will be more than 2 wires in the conduit, you'll have to use the 40% fill column. Even with area reduction, you'll still be able to use 3/4" conduit instead of 1".