Chapter 9 Note 2

[ludwigbayer]

I'm somewhat confused by this note, can someone explain?
"Table 1 applies only to complete conduit or tubing systems and is not intended to apply to sections of conduit or tubing used to protect exposed wiring from physical damage."

1. What else would conduit be used for, if not physical protection?
2. What constitutes a "complete conduit or tubing system"?

A company provided two pieces of equipment that need to be wired to one another, that are about 6ft apart. Do I have to worry about fill rates in this instance?

Thank you!

 

[K8MHZ]

One example of an incomplete system would be a short piece of EMT going from a box to free air to protect NM cable installed on a concrete basement wall.

I would say yes, conduit terminating at equipment on both ends would be a complete system.

 

[ludwigbayer]

One example of an incomplete system would be a short piece of EMT going from a box to free air to protect NM cable installed on a concrete basement wall.

I would say yes, conduit terminating at equipment on both ends would be a complete system.

Alright, thank you.

Now on to the next question, I thought the purpose of the conduit fill is for:
a. Being able to pull the cable without damaging it
b. (maybe?) conductor temperature requirements.

If a and not b, then why would I care for a very short run where that won't be an issue at all?
If b and a, I'm pretty sure I can give engineering justification for not having to worry about the temperature being an issue. Any pointers on this?

Thanks a bunch!

 

[Dennis Alwon]

As soon as the conduit is more than 2' then fill becomes an issue. It is not just for pull but for heat dissipation also

 

[GoldDigger]

There are two separate sets of rules which are not identical:
1. Fill rules tell you what percentage of raceway may be filled with wire and insulation whether current is carried or not.
2. Adjustments to ampacity based on the number of current carrying conductors regardless of size. And with temperature correction that does not depend on fill or CCC either.

 

[Smart $]

...
A company provided two pieces of equipment that need to be wired to one another, that are about 6ft apart. Do I have to worry about fill rates in this instance?

...I'm pretty sure I can give engineering justification for not having to worry about the temperature being an issue. Any pointers on this?...

If that company provided the wiring between the two pieces are part of total listed equipment package, then that interconnection does not fall under the NEC... except for AHJ approval. Hard to say if the AHJ will evaluate its approval without using the NEC as its guide though.

If not supplied by manufacturer, then note adjustment for number of current-carrying conductors under Table 310.15(B)(3)(a) only apply to power and lighting conductors... but that has no bearing on fill. Fill requirements will apply if the conduit is complete from enclosure to enclosure.

 

[infinity]

Alright, thank you.

Now on to the next question, I thought the purpose of the conduit fill is for:
a. Being able to pull the cable without damaging it
b. (maybe?) conductor temperature requirements.

If a and not b, then why would I care for a very short run where that won't be an issue at all?
If b and a, I'm pretty sure I can give engineering justification for not having to worry about the temperature being an issue. Any pointers on this?

Thanks a bunch!

Conduit fill limitations are only for a. The purpose for limiting fill is protect the conductors during installation.