Conduit fill

[Crabcakes&football]

How many #16 can I get in a 3/4 emt? As far as I can see the table only goes up to #14. Any code reference that can help me figure this out.

 

[infinity]

What is the insulation type? Table C1 under Fixture Wires starts at 18 AWG.

 

[winnie]

The basic requirement in the NEC is that when you have 3 or more conductors in a conduit, the total cross section of the conductors must be no more than 40% of the open cross section of the conduit. (There are different % values for 1 and 2 conductors, and special rules for conductors that are not round, ignoring those here.)

The formula for the area of a circle is pi/4*D^2, but since the pi and the 4 are constants we can just ignore them and work with diameter squared.

3/4 EMT has an inner diameter of 0.824"

The diameter of the wire depends on the insulation type and stranding. For example 16 MTW wire has an outer diameter of 0.124".

0.824^2 / 0.124^2 * 0.4 = 17.66 so you are permitted to put 17 of this size wire in a 3/4 EMT.

16 solid TFFN has a diameter of 0.089", so far more would be permitted. So you will need to figure out exactly what sort of wire you are trying to install before you can get a solid answer for max number permitted.

-Jon

 

[petersonra]

The diameter of the wire depends on the insulation type and stranding. For example 16 MTW wire has an outer diameter of 0.124".

0.824^2 / 0.124^2 * 0.4 = 17.66 so you are permitted to put 17 of this size wire in a 3/4 EMT.

Are you allowed to put MTW in a conduit at all? Table 310.15(B)(16) does not list it. In any case if it is #16 it would likely be class 1 circuits. In that case article 725.3 would govern, which sends you to 300.17. Which leaves the number of conductors up in the air.

 

[winnie]

Are you allowed to put MTW in a conduit at all? Table 310.15(B)(16) does not list it. In any case if it is #16 it would likely be class 1 circuits. In that case article 725.3 would govern, which sends you to 300.17. Which leaves the number of conductors up in the air.

Thus the core reason that this isn't a DIY site. I don't know why someone wants to put #16 into a conduit. I don't know what _other_ codes they need to follow with the installation. They ask a specific question about conduit fill, and I try to answer with the math, trusting that as a professional if there is some other bit of the install they don't understand they will ask about that.

But you are absolutely correct: MTW probably can't go into a conduit, though it is probably rated with other insulation types that are permitted in a conduit, and #16 is almost certainly not for a power circuit since those are generally limited to 14 awg and above.

-Jon

 

[masterinbama]

Thus the core reason that this isn't a DIY site. I don't know why someone wants to put #16 into a conduit. I don't know what _other_ codes they need to follow with the installation. They ask a specific question about conduit fill, and I try to answer with the math, trusting that as a professional if there is some other bit of the install they don't understand they will ask about that.

But you are absolutely correct: MTW probably can't go into a conduit, though it is probably rated with other insulation types that are permitted in a conduit, and #16 is almost certainly not for a power circuit since those are generally limited to 14 awg and above.

-Jon

Pull it quite often for control work.

Also derating doesn't apply in control work.

Sent from my moto e using Tapatalk

 

[don_resqcapt19]

.... In that case article 725.3 would govern, which sends you to 300.17. Which leaves the number of conductors up in the air.

How does a reference to 300.17 leave the raceway fill up in the air. That is the reference used throughout the code for raceway fill. The Informational Note there, sends you to the xxx.22 sections of the raceway articles and those sections in turn send you to Chapter 9, Table 1 for the actual rule.

 

[petersonra]

informational notes are not enforceable. since 725.3 does not refer to the actual paragraphs like 344.22 that refer to chapter 9, table 1, how would such a limit be enforceable?

90.5 Mandatory Rules, Permissive Rules, and Explantory
Material.
(A) Mandatory Rules. Mandatory rules of this Code are those
that identify actions that are specifically required or prohibited
and are characterized by the use of the terms shall or shall not.
(B) Permissive Rules. Permissive rules of this Code are those
that identify actions that are allowed but not required, are
normally used to describe options or alternative methods, and
are characterized by the use of the terms shall be permitted or
shall not be required.
(C) Explanatory Material. Explanatory material, such as references
to other standards, references to related sections of this
Code, or information related to a Code rule, is included in this
Code in the form of informational notes. Such notes are informational
only and are not enforceable as requirements of this
Code.

725.3 Other Articles. Circuits and equipment shall comply
with the articles or sections listed in 725.3(A) through (N).
Only those sections of Article 300 referenced in this article
shall apply to Class 1, Class 2, and Class 3 circuits.
(A) Number and Size of Conductors in Raceway.
Section 300.17.

 

[don_resqcapt19]

informational notes are not enforceable. since 725.3 does not refer to the actual paragraphs like 344.22 that refer to chapter 9, table 1, how would such a limit be enforceable?

The note itself is not enforceable but the code sections that the note refers too are. There are many examples of this in the code ... places where a note is used to send you to enforceable code rules.

 

[petersonra]

The note itself is not enforceable but the code sections that the note refers too are. There are many examples of this in the code ... places where a note is used to send you to enforceable code rules.

Article 725 very clearly says that only those parts of chapter 3 that are referenced are part of article 725.

 

[don_resqcapt19]

Article 725 very clearly says that only those parts of chapter 3 that are referenced are part of article 725.

That is not what 725.3 actually says. It says Article 300, not Chapter 3.

725.3 Other Articles.
In addition to the requirements of this article, circuits and equipment shall comply with the articles or sections listed in 725.3(A) through (P). Only those sections of Article 300 referenced in this article shall apply to Class 1, Class 2, and Class 3 circuits.

 

[Crabcakes&football]

The basic requirement in the NEC is that when you have 3 or more conductors in a conduit, the total cross section of the conductors must be no more than 40% of the open cross section of the conduit. (There are different % values for 1 and 2 conductors, and special rules for conductors that are not round, ignoring those here.)

The formula for the area of a circle is pi/4*D^2, but since the pi and the 4 are constants we can just ignore them and work with diameter squared.

3/4 EMT has an inner diameter of 0.824"

The diameter of the wire depends on the insulation type and stranding. For example 16 MTW wire has an outer diameter of 0.124".

0.824^2 / 0.124^2 * 0.4 = 17.66 so you are permitted to put 17 of this size wire in a 3/4 EMT.

16 solid TFFN has a diameter of 0.089", so far more would be permitted. So you will need to figure out exactly what sort of wire you are trying to install before you can get a solid answer for max number permitted.

-Jon

TFFN

 

[petersonra]

That is not what 725.3 actually says. It says Article 300, not Chapter 3.

This is what it says.

725.3 Other Articles. Circuits and equipment shall comply
with the articles or sections listed in 725.3(A) through (N).
Only those sections of Article 300 referenced in this article
shall apply to Class 1, Class 2, and Class 3 circuits.

My take is the only time anything in any other article applies in article 725 is if it specifically says so. There are a handful of things in article 300 and one thing in article 310 mentioned in 725.3(A) through (N). Those would be the only parts of chapter three that apply, unless there are some other references later in article 725.

 

[winnie]

TFFN

Solid or stranded? It makes a difference.

So assuming _solid_ TFFN you have 0.824^2 / 0.089^2 * 0.4 = enough to be a pain in the donkey (34 )

-Jon