THHN vs XHHW

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Vertex

Senior Member
Assuming wire is not subjected to sunlight or in a harsh environment and given the choice, would you rather use THHN/THWN or XHHW? Please support your preference.
 

Dennis Alwon

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I have not use xhhw much but if you are going for conduit fill then xhhw is a bit smaller than thhn/thwn but I like the thermoplastic on thhn
 
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iwire

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Staff member
Location
Massachusetts
THHN/THWN is smaller and slicker, much easier to work with.

XHHW is in my opinion a much more durable insulation but it is tougher and larger.

As a customer I would want XHHW, as an installer THWN.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
XHHW is more expensive also. $259/ CLF for 1/0 THWN-THHN, vs. $425 for XHHW from my price guide.

I don't know the answer Dennis maybe I am wrong but I can tell you it is not easy to work with.

But they list the same labor for installation of both types of wire. I guess they don't care if electricians have to work harder, as long as it doesn't take longer :)
 

jdsmith

Senior Member
Location
Ohio
From an owner's perspective there is a substantial difference in the performance of the two insulating materials. THHN and THWN are constructed of PVC insulation with a sacrificial nylon outer jacket, XHHW has XLPE insulation (cross-linked polyethylene.) PVC is the cheapest insulating material available. It performs suitably in dry conditions, but moisture and water exposure can ruin it fairly quickly compared to XLPE, CPE, EPR, and other insulating materials.

XLPE is a superior conductor insulation by far. XLPE has a higher dielectric strength per mil of thickness. XLPE lasts much longer in the presence of moisture, at least at low voltages with electric field strengths too low to cause water treeing. XLPE is a tougher, more durable material that is not as susceptible to tears and rips during installation. As an owner we require everything to be meggered after pulling, but unless a conduit is flooded with water before meggering the megger will not detect these tears in the insulation. The dielectric constant of XLPE is less than half of the dielectric constant of PVC, which means the capacitance of XLPE insulated cables is much lower. The cable capacitance has a large impact on smaller VFDs because the charging current of the cable can be higher than the motor current, and the VFD has to source the charging current and the motor current. If the drive isn't sized for both nuisance overcurrent trips will result.

The choice of the best insulation depends on the type of facility. For indoor locations not subject to abnormal moisture or condensation THHN/THWN is appropriate. For locations where longevity is not important because the electrical infrastructure is frequently modified or replaced THHN/THWN is appropriate. For wet locations where the conductors will see 15 years or more of service XHHW is probably worth the money. In my case in an outdoor process plant where most of our plant is 40-60 years old and still operating with minimal modifications since it was installed XHHW is certainly most economical over the life cycle of the cable.
 

jetlag

Senior Member
I have not use xhhw much but if you are going for conduit fill then xhhw is a bit smaller than thhn/thwn but I like the thermoplastic on thhn

not used xhhw ? isn't thats what used in se cable ? Also what ever is used in use-2 cable is dual rated and can be used in same location as xhhw, can be used up a mast to weather head, it is compact and easy to bend. ;)
 

Vertex

Senior Member
From an owner's perspective there is a substantial difference in the performance of the two insulating materials. THHN and THWN are constructed of PVC insulation with a sacrificial nylon outer jacket, XHHW has XLPE insulation (cross-linked polyethylene.) PVC is the cheapest insulating material available. It performs suitably in dry conditions, but moisture and water exposure can ruin it fairly quickly compared to XLPE, CPE, EPR, and other insulating materials.

XLPE is a superior conductor insulation by far. XLPE has a higher dielectric strength per mil of thickness. XLPE lasts much longer in the presence of moisture, at least at low voltages with electric field strengths too low to cause water treeing. XLPE is a tougher, more durable material that is not as susceptible to tears and rips during installation. As an owner we require everything to be meggered after pulling, but unless a conduit is flooded with water before meggering the megger will not detect these tears in the insulation. The dielectric constant of XLPE is less than half of the dielectric constant of PVC, which means the capacitance of XLPE insulated cables is much lower. The cable capacitance has a large impact on smaller VFDs because the charging current of the cable can be higher than the motor current, and the VFD has to source the charging current and the motor current. If the drive isn't sized for both nuisance overcurrent trips will result.

The choice of the best insulation depends on the type of facility. For indoor locations not subject to abnormal moisture or condensation THHN/THWN is appropriate. For locations where longevity is not important because the electrical infrastructure is frequently modified or replaced THHN/THWN is appropriate. For wet locations where the conductors will see 15 years or more of service XHHW is probably worth the money. In my case in an outdoor process plant where most of our plant is 40-60 years old and still operating with minimal modifications since it was installed XHHW is certainly most economical over the life cycle of the cable.

Thank you JD. That was very insightful.
 
Assuming wire is not subjected to sunlight or in a harsh environment and given the choice, would you rather use THHN/THWN or XHHW? Please support your preference.

The fundamental difference between the two wires are the thermal response to overload and short circuit.

TH** is thermoplastic and XHHW is thermosetting. In the case of overload or external ehat that pushes the insulation to it's thermal limits the thermosetting material will harden to eventual brittleness, while the thermoplastic material softens. So ground fault and phase-to-phase fault is more likely in the case of thermoPLASTIC materials.
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
...
As an owner we require everything to be meggered after pulling, but unless a conduit is flooded with water before meggering the megger will not detect these tears in the insulation. ...
This is a point I have tried to make a number of times on this site with very limited success.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
The fundamental difference between the two wires are the thermal response to overload and short circuit.

TH** is thermoplastic and XHHW is thermosetting. In the case of overload or external ehat that pushes the insulation to it's thermal limits the thermosetting material will harden to eventual brittleness, while the thermoplastic material softens. So ground fault and phase-to-phase fault is more likely in the case of thermoPLASTIC materials.

Huh?

THHN softens? When? I can't count how many times I've pulled a T-lead off a burned up starter and the insulation is black, cracked and brittle.
 

mbeatty

Senior Member
Location
Illinois
THHN vs XHHW

I agree with jdsmith's statements pertaining to THHN and XHHW. I usually specify THHN/THWN-2 for our equipment, but have used XHHW depending on ambient conditions.
Regards,
Mark :)
 
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