To find the maximum number of conductors allowed in a conduit with all of the conductors of the same size and type of insulation. You must refer to the NEC Appendix “C” in the back of the book. You must refer to the table representing the type of conduit that you are using to find the maximum number of conductors allowed within the conduit you are using.

To discover where you can find the chart pertaining to the certain conduit that you are using with all the same type insulation and conductor size in that conduit, then jump down to the last section of this article where it shows and list each conduit, and where the chart for that conduit fill can be found. Remember that the list of charts in the last section of this article pertains only to conduit fill of all the same type insulation and conductor size contained in that certain conduit.

**Special
Notes:** In real life installation you will find
it much better if you install only 1/2 of the maximum number of conductors
allowed by the NEC Code in a certain conduit. You can run two conduits
parallel to each other much easier and faster than you can if you were
trying to force the maximum number of wires into the conduit that the
NEC Code allows. You will find 1/2 of the maximum allowed to be faster,
easier, and cheaper in the long run. If you considerNEC
Table 310.15.B.2.Aconcerning
conductor ampacity de-ration requirements of more than 4 conductors in
a raceway or conduit you will also lose ampacity of that conductor to
a level of being detrimental to your design purposes if you go much more
than four conductors in a raceway. This is true unless you are dealing
with a lightly loaded circuit concerning low load amps such as motor
control relay circuits, or a signaling relay circuit, that will pull
such a minor amp draw that the loss of ampacity will not affect your
design purposes.

**Special
Notes:** Conduit fill calculations are not intended
to apply to short sections of conduit that are used only to protect exposed
wires [such as Romex] from physical damage. Conduit fill calculations pertain
only to certain wiring designed sections that is substantially conduit
in design. NEC Chapter 9 Notes to tables Note
2

**Special
Notes:** Grounding {bonding} and grounded conductors
whether bare or insulated shall be counted in your conduit fill calculations.
Also often times when installing metal conduit and metal boxes the conduit
is commonly used as the equipment grounding conductor as allowed by the
NEC.NEC Chapter 9 Notes to tables Note 3
and NEC Article 250.118

**Special
Notes:** When bare wires are within your calculations
of different types insulation and different sizes of conductors you must
calculate those bare wires separately from all others in their own special
calculation. See circular mill in NEC Chapter
9 Table 8 then add this calculation
into your summation because a bare wire takes up less area of fill than
an insulated conductor does yet each individual bare or green grounding
conductor still must be counted in your calculation. NEC
Chapter 9 Notes to tables Note 3

**Special
Notes:** NEC APPENDIX “C” is
not intended to be used with nipples less than 24”long. A nipple
less than 24”long shall be calculated at 60% fill allowed instead
of the usual 40% fill allowed for more than 2 conductors in a conduit whether
current carrying or not. NEC Chapter 9 Notes
to tables Note 4

**Special
Notes:** When installing multi - conductor cable
such as Romex in a conduit you must calculate the actual dimensions of
the cable at it’s widest point, and calculate this Cable as a circular
assembly same as a single conductor . Then compare this area required to
the 40% fill allowed for the conduit being used.NEC
Chapter 9 Notes to tables Note 9

**Special
Notes:** When your calculations results land in a
decimal of point .8 or larger you must adjust to the next higher number
of conductors. NEC Chapter 9 Notes to tables
Note 7

**Special
Notes:**This is the only time you must adjust up
from .8 or larger instead of .5 or larger such as in resistance calculations.
This is the one ringer I was telling you about that you will probably find
on a test. The answer you can bet will land on .5 for resistance or .8
for conductor fill.

**NEC Chapter 9 Table 4 and NEC Chapter 9 Notes to tables Note 7 **

Remember it is .5 for resistance or .8 for conduit fill requirements, and when you land on the number, adjust up.

**Special
Notes:** Remember 40% fill allowed in a conduit with
more than two conductors in a raceway. This is the column you will most
commonly use to calculate conduit fill allowed for conductors of different
types and sizes in the same conduit. NEC Chapter
9 Table 4

**Special
Notes:** When calculating conductors of different
sizes and types of insulation in a conduit fill calculation you must useNEC
Chapter 9 Table 4 forfinding
the dimensions and percent of area allowed. You must useNECChapter
9 Table 5for dimensions of
insulated conductors for both copper and aluminum and,NECChapter
9 Table 5Afor dimensions of
insulated conductors for compact aluminum wires now being found on the
market.

**Special
Notes:** When calculating number of conductors with
all of the same size and insulation useNEC
Appendix “C”. found at the bottom
of this article

**Special
Notes:** Conduit fill does not apply to those pieces
of conduit used only for a form of protection and is not a part of a
complete conduit or tubing system. NEC
Chapter 9 Notes to tables Note 2

**Special
Notes:** In conduit fill calculations you must count
the grounding or bonding conductors. Remember that if that grounding conductor
is bare useNECChapter
9 Table 8using the column for
area of square inch of bare conductors.

**Special
Notes:** When calculating
conductors of different size useNEC
Tables 5 to apply the dimensions of the conductor
for normal non compact style conductors ,and
5A in Chapter 9to apply the
dimensions of the compacted style conductors, and then useNECTable
4 in Chapter 9to apply dimensions
of the conduit.

**Example #1:**

What size Electrical Metallic Tubing is required for the following conductors ?

5- # 14 THW 11 - # 12 TW 8 - # 10 THHN 7 - # 8 THWN

To find the
area in square in. of conductors, we must go to ** NEC
Chapter 9 Table 5****.** Then multiply the
areas of square inch by the number of conductors. The areas of square inch
of the above conductors are as follows;

# 14 THW = .0209 x 5 CONDUCTORS = .1045 SQUARE INCH

# 12 TW = .0181 x 11 CONDUCTORS = .1991 SQUARE INCH

# 10 THHN = .0211 x 8 CONDUCTORS = .1688 SQUARE INCH

# 8 THWN = .0366 x 7 CONDUCTORS = .2562 SQUARE INCH

Total square inch of conductors used .7286 SQUARE INCH

Now you must compare that to the area of square inch for over 2 wires found in

NEC Chapter 9 Table 4for an Electrical Metallic Tubing at the allowable 40% fill, and you will find that a 1 1/2”Electrical Metallic Tubing will be required, because the next size smaller conduit is only .598 square inch, which is smaller than the required .7286 square inch we calculated as being required for the wires we intend to use.

**Example #2:**

What size Rigid Nipple is required for the following conductors ?

5- # 14 THW 11 - # 12 TW 8 - # 10 THHN 7 - # 8 THWN

# 14 THW = .0209 x 5 CONDUCTORS = .1045 SQUARE INCH

# 12 TW = .0181 x 11 CONDUCTORS = .1991 SQUARE INCH

# 10 THHN = .0211 x 8 CONDUCTORS = .1688 SQUARE INCH

# 8 THWN = .0366 x 7 CONDUCTORS = .2562 SQUARE INCH

Total square inch of conductors used .7286 SQUARE INCH

**Special
Notes:** You should remember that a nipple may
be filled to 60% of the total area 100% square inch column. This is found
in the NEC Chapter 9 Table 4 for
a rigid conduit = 1 1/4”nipple = 1.526 x 60 % = .9156 square inch
which is larger than the total square inch of conductors used .7286.
A 1”nipple = .888 x 60%=.5328 square inch which is too small. The
answer would be 1 1/4”.

**Example #3**

What size Rigid Conduit is required for the following conductors ?

5- # 14 BARE 11 - # 12 TW 8 - # 10 THHN 7 - # 8 THWN

**Special
Notes:** Remember for bare wires you must refer toNEC
Chapter 9 Table 8 look for area
in.2

# 14 BARE = .003 x 5 CONDUCTORS = .0150 SQUARE INCH

# 12 TW = .0181 x 11 CONDUCTORS = .1991 SQUARE INCH

# 10 THHN = .0211 x 8 CONDUCTORS = .1688 SQUARE INCH

# 8 THWN = .0366 x 7 CONDUCTORS = .2562 SQUARE INCH

Total square inch of conductors used .6391 SQUARE INCH

Now you must compare that to the area of square inch for over 2 wires in a rigid metallic conduit at the allowable 40% fill and you will find that a 1 1/2”with .829 square inch for a rigid metallic conduit will be required because the next size smaller 1 1/4”is only .610 square inch which is smaller that the required .6391 square inch we received from our calculation.

**Special
Notes:** The rounding to the next size
larger did not come up in our calculations to this point. Remember the
.08 or larger must be rounded up to the next size higher whole number.

Using all the same types insulation and all the same size conductors within that certain conduit you may use the following charts found in appendix "C."

**Step One**

To find the maximum number of conductors and fixture wires in electrical metallic tubing (EMT)--thin wall--you must refer to the NEC Table "C1," in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical metallic tubing (EMT)--thin wall--for (compact) wires you must refer to NEC Table "C1A" in the NEC Appendix "C" in the back of the book.

**
Step Two**

You must then refer to the type of insulation your conductors has THW / THHN / THWN / XHHW / etc.

**
Step Three**

You must then refer to the conductor size in AWG. or KCMIL or MCM.

**
Step Four**

You must then refer to the column that refers to the number of conductors you want to install.

**
Final Step**

Once you find the number of conductors corresponding with the insulation type and conductor size then look up at the top of the chart in that column corresponding with the number of conductors that you want and it will tell you the minimum trade size EMT conduit that you must use.

**ENT:** To find the maximum number of conductors and fixture wires in electrical non-metallic tubing (ENT)--blue smurf pipe--you must refer to NEC Table "C2" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical non-metallic tubing (ENT)--blue smurf pipe--for (compact) wires you must refer to NEC Table "C2A" in the NEC Appendix "C" in the back of the book.

**FLEX:** To find the maximum number of conductors and fixture wires in electrical flexible metallic tubing (flex) you must refer to NEC Table "C3" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical flexible metallic tubing (flex) for (compact) wires you must refer to NEC Table "C3A" in the NEC Appendix "C" in the back of the book.

**IMC:** To find the maximum number of conductors and fixture wires in electrical intermediate metallic conduit (IMC)--usually threaded aluminum--you must refer to NEC Table "C4" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical intermediate metallic conduit (IMC)--usually threaded aluminum--for (compact) wires you must refer to NEC Table "C4A" in the NEC Appendix "C" in the back of the book.

**FNMC-B:** To find the maximum number of conductors and fixture wires in electrical liquidtight flexible non-metallic conduit (Type FNMC-B )--This type of flexible tubing may be used as a building wiring method (NEC 351-22 (2))--you must refer to NEC Table "C5" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical liquidtight flexible non-metallic tubing (Type FNMC-B) for (compact) wires you must refer to NEC Table "C5A" in the NEC Appendix "C" in the back of the book.

**FNMC-A:** To find the maximum number of conductors and fixture wires in electrical liquidtight flexible non-metallic conduit (Type FNMC-A)--This type of flexible tubing is limited to lengths of 6' and may not be used as a building wiring method (NEC 351-22 (1))--you must refer to NEC Table "C6" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical liquidtight flexible non-metallic tubing (Type FNMC-A for (compact) wires you must refer to NEC Table "C6A" in the NEC Appendix "C" in the back of the book.

**Sealtite:** To find the maximum number of conductors and fixture wires in electrical liquidtight flexible metallic conduit (Sealtite) you must refer to NEC Table "C7" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical liquidtight flexible metallic conduit (Sealtite) for (compact) wires you must refer to NEC Table "C7A" in the NEC Appendix "C" in the back of the book.

**Rigid Metallic Conduit:** To find the maximum number of conductors and fixture wires in electrical rigid metallic conduit--threaded rigid heavy wall steel--you must refer to NEC Table "C8" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical rigid metallic conduit--threaded rigid heavy wall steel--for (compact) wires you must refer to NEC Table "C8A" in the NEC Appendix "C" in the back of the book.

**Rigid Non-Metallic Conduit (Heavy Wall):** To find the maximum number of conductors and fixture wires in electrical rigid non-metallic conduit schedule 80--(heavy wall) (PVC Sch. 80) (can be used where subject to physical damage)--you must refer to NEC Table "C9" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical rigid non-metallic conduit schedule 80--(heavy wall) (PVC Sch. 80) (can be used where subject to physical damage)--for (compact) wires you must refer to NEC Table "C9A" in the NEC Appendix "C" in the back of the book.

**Rigid Non-Metallic Conduit (Light Wall):** To find the maximum number of conductors and fixture wires in electrical rigid non-metallic conduit schedule 40--(light wall) (PVC Sch. 40) (can not be used where subject to physical damage)--you must refer to NEC Table "C10" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in electrical rigid non-metallic conduit schedule 40--(light wall) (PVC Sch. 40) (cannot be used where subject to physical damage)--for (compact) wires you must refer to NEC Table "C 10 A", in the NEC Appendix "C" in the back of the book.

**Rigid PVC Conduit Type A:** To find the maximum number of conductors and fixture wires in rigid PVC conduit Type A you must refer to NEC Table "C11" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in rigid PVC conduit Type A for (compact) wires you must refer to NEC Table "C11A" in the NEC Appendix "C" in the back of the book.

**Rigid PVC Conduit Type EB:** To find the maximum number of conductors and fixture wires in rigid PVC conduit Type EB you must refer to NEC Table "C12" in the NEC Appendix "C" in the back of the book, and to find the maximum number of conductors and fixture wires in rigid PVC conduit type EB for (compact) wires you must refer to NEC Table "C12A" in the NEC Appendix "C" in the back of the book.

**Final Special Note**

There is more than just one page per chart. For an example NEC Table "C1" contains five pages of tables just for electrical metallic tubing. These multi-page table charts are required just to list the different types of conductor insulation that are normally used in the electrical industry. Each Table contains several pages of tables that are still a part of that one certain table section.

*This document is based on the 2002 national electrical code and is designed
to give you an option, as a self-help, that should pass minimum code requirements.
While extreme care has been implemented in the preparation of this self-help
document, the author and/or providers of this document assumes no responsibility
for errors or omissions, nor is any liability assumed from the use of the
information, contained in this document, by the author and / or provider.*

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