Conduit Fill - Wrapped THHN

Status
Not open for further replies.
A

ACI

Member
Location
WI
Occupation
Engineering
We are attempting to understand conduit fill as it relates to bundled or wrapped wire (THHN). If a group of THHN (5-14 AWG & 5-18 AWG) are wrapped (to keep the group organized) vs individual THHN (5-14 AWG & 5-18 AWG). Would the wrap make a difference in the size fill calculation?
 
What kind of wrap are you referring to? Like a "quick pull"?

690e0134-e2f3-44e6-8c59-72bfca989e44.jpeg
 
I don't think that the NEC directly addresses wrapped conductors. It could be argued that they're actually separate conductors so normal conductor fill applies. Or it can be argued that they are in effect a single conductor then the rules for a single conductor in a raceway would apply. Without doing some calculations I wonder if it would even matter one way or the other.
 
ptonsparky said:
That would certainly depend on how they are wrapped.
Click to expand...
If you mean a larger conductor as in based on the diameter of the wrapped bundle being a single conductor, I tend to agree. I would use common sense and caution. If the bundle is tightly wrapped, I would avoid fill over 30% if there were only two. For a single bundle I would likely avoid anything over 40% for multiple wires. However, if they are tightly wrapped, then using a caliper and using that diameter for a 53% fill would be acceptable IMO, I just wouldn't put myself through the attempt to pull that unless I absolutely needed to use the small conduit.
 
I would post the question: Does that constitute some conductors or is it a cable? (I don't know the answer)
 
Strathead said:
For a single bundle I would likely avoid anything over 40% for multiple wires. However, if they are tightly wrapped, then using a caliper and using that diameter for a 53% fill would be acceptable IMO, I just wouldn't put myself through the attempt to pull that unless I absolutely needed to use the small conduit.
Click to expand...
That would only be beneficial (in terms of having the calculation meet the limits) if you have 7 conductors in the bundle (or 18 or more, possibly). That's because 40% / 53% = 0.754, and for a small number of circles packing inside a larger circle, the only number between 2 and 17 that achieves a density greater than that is 7 conductors (in the usual hexagonal pattern).

Circle packing in a circle - Wikipedia

en.wikipedia.org en.wikipedia.org

Cheers, Wayne
 
tortuga said:
I dont consider quick pull a cable nor do I add anything extra for it.
Click to expand...
Tortuga,

I would agree, we never consider individual wrapped THHN wires a cable. It is a "bundle", but we always consider these as individual THHN wires for the purpose of NEC calculations.
 
ACI said:
Would the wrap make a difference in the size fill calculation?
Click to expand...
In my opinion, the main difference made by the wrap would be in heat dissipation.

For conduit sizing, a cable is considered a single conductor of the same overall size.

How would sizing for a cable vs for individual conductors affect the conduit size needed?
 
ACI said:
We are attempting to understand conduit fill as it relates to bundled or wrapped wire (THHN). If a group of THHN (5-14 AWG & 5-18 AWG) are wrapped (to keep the group organized) vs individual THHN (5-14 AWG & 5-18 AWG). Would the wrap make a difference in the size fill calculation?
Click to expand...
I would say no. It is not a conductor.
I don't believe the NEC address it.
I have to admit I was thinking about it for a minute.

Then I was thinking what if I pulled two groups of wrapped conductors and how I would address the fill. Not for NEC fill rather pulling. It would be like two larger conductors and a ID/OD and a possible jam ratio.

I may need to run some number to see if it's applicable.

Using a number of wires into two bundles. Versus number of wires. Based on raceway size.

I would not think one would be doing two or more bundles per pull however they may.
 
Status
Not open for further replies.
Top