XHHW-2 or THWN-2

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jjavier

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Hi

I asked for quotation for cable THWN-2 aluminum and it is more expensive than XHHW-2. I thought that XHHW-2 was better cable, wasn't it? What is the cheaper one?

What do you think is the best quality/price aluminium cable for underground pvc conduit?

Regards
 
It is probably cheaper because it is sold more often than the individual conductors of Thwn-2. I believe xhhw is a more rugged insulation and a bit smaller in area than thwn-2.

My supplier only sells the xhhw as a quadraplex so the pull may be a bit harder than individual conductors- Larger pipe perhaps
 
As others have said, it probably depends on what is more commonly sold/distributed in an area. Here single conductor al is always xhhw. If you want colors, you order it and it is thhn. Recently, when I have ordered colors, they have given me the option of xhhw or thhn, but I don't recall if there is a price difference. I am usually mostly ambivalent, but xhhw is a bit tougher. When I get larger al mc cable, I have seen the inners with both types.
 
Dennis Alwon said:
It is probably cheaper because it is sold more often than the individual conductors of Thwn-2. I believe xhhw is a more rugged insulation and a bit smaller in area than thwn-2.

My supplier only sells the xhhw as a quadraplex so the pull may be a bit harder than individual conductors- Larger pipe perhaps
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I think it pulls easier then individual conductors - because it acts like one instead of three or four.

Also keep in mind if triplexed or quadraplexed it is one cable, and your raceway fill jumps to 53% allowable for one conductor or cable, but is based on overall diameter of the bundle and not each individual conductor.
 
kwired said:
Also keep in mind if triplexed or quadraplexed it is one cable, and your raceway fill jumps to 53% allowable for one conductor or cable, but is based on overall diameter of the bundle and not each individual conductor.
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The packing factor of three wires in a triplexed bundle, for how they fit in the overall bundle diameter is 65%.
65% of 53% = 34.5%

Which percentage should govern? The 34.5% based on how the triplexed bundle fits as if it were a single conductor? Or the 40%, based on how the three conductors fit if they were individual conductors?
 
Carultch said:
The packing factor of three wires in a triplexed bundle, for how they fit in the overall bundle diameter is 65%.
65% of 53% = 34.5%

Which percentage should govern? The 34.5% based on how the triplexed bundle fits as if it were a single conductor? Or the 40%, based on how the three conductors fit if they were individual conductors?
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If it is a cable, it has to be a type recognized by the NEC as a cable. If not, "they" are single conductors.
 
XHHW-2 simply plexed or twisted together doesn't make them a cable and it doesn't permit them to fill a raceway to 53%....been preaching this for years but the 2017 NEC made that clear in Chapter 9, Table 1 note 9.

Comments based on the 2017 National Electrical Code.
 
MasterTheNEC said:
XHHW-2 simply plexed or twisted together doesn't make them a cable and it doesn't permit them to fill a raceway to 53%....been preaching this for years but the 2017 NEC made that clear in Chapter 9, Table 1 note 9.
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Here it is... new underlined.
(9) A multiconductor cable, optical fiber cable, or flexible
cord of two or more conductors shall be treated as a single
conductor for calculating percentage conduit or tubing
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.
Assemblies of single insulated conductors without an
overall covering shall not be considered a cable when
determining conduit or tubing fill area. The conduit or
tubing fill for the assemblies shall be calculated based
upon the individual conductors.
Click to expand...
 
MasterTheNEC said:
XHHW-2 simply plexed or twisted together doesn't make them a cable and it doesn't permit them to fill a raceway to 53%....been preaching this for years but the 2017 NEC made that clear in Chapter 9, Table 1 note 9.

Comments based on the 2017 National Electrical Code.
Click to expand...

It is more conservative to treat a triplex of wires as a single cable, than it is to treat the wires as individual wires. While 53% looks higher than 40%, that 53% would also includes the gray void space as shown in the following diagram. So that means limiting the gray+black region to 53% of the total, means limiting the black region to 34.5% of the total.

120px-Disk_pack3.svg.png
 
LOL....i treat it by what the NEC says......twisting wire doesn't make it a cable...plain and simple. You can do as you wish....lol

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Carultch said:
It is more conservative to treat a triplex of wires as a single cable, than it is to treat the wires as individual wires. While 53% looks higher than 40%, that 53% would also includes the gray void space as shown in the following diagram. So that means limiting the gray+black region to 53% of the total, means limiting the black region to 34.5% of the total.
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Not by much.

34.5% as a cable vs. 40% as individual conductors.
 
I still find multiplexed conductors easier to pull then single conductors in general, I believe it is because they act like a single conductor/cable to some extent. Now they are a big PITA if you have a conduit body that isn't oversized in the run unless maybe it is just a short length after the conduit body to an enclosure that those conductors will terminate in.
 
kwired said:
I still find multiplexed conductors easier to pull then single conductors in general, I believe it is because they act like a single conductor/cable to some extent. Now they are a big PITA if you have a conduit body that isn't oversized in the run unless maybe it is just a short length after the conduit body to an enclosure that those conductors will terminate in.
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Agreed. Basically it boils down to the coefficient of friction and surface contact points. While pre-twisting doesn't evoke the 53% fill....the reduction of "in contact" surface area aids the pull in general.

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MasterTheNEC said:
Agreed. Basically it boils down to the coefficient of friction and surface contact points. While pre-twisting doesn't evoke the 53% fill....the reduction of "in contact" surface area aids the pull in general.

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Click to expand...

Surface area in contact does not affect friction. It affects the local pressure due to friction, but not the overall relation between friction and constraint force.
 
Carultch said:
Surface area in contact does not affect friction. It affects the local pressure due to friction, but not the overall relation between friction and constraint force.
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Then why do dragsters run on racing slicks?
 
ggunn said:
Then why do dragsters run on racing slicks?
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Because the traction pounds per square inch matters in addition to the total traction pounds. The traction pounds per square inch affects the mechanical loading of the rubber. It is not only about getting a better grip, but also being able to safely withstand that better grip, without rupture.
 
"Because the traction pounds per square inch matters in addition to the total traction pounds." The surface area versus pounds per foot of wire function nearly the same. In our labs the surface area directly affects the COF values and when plexed (which we only do on request) along with super slick. We have conducted tests with all scenario 's considered.

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