Choosing the building wire between THHN and XHHW
Choosing the right building wire for constructing a new facility is the biggest challenge for an engineer or an electrical technician and such common types of conductors are THHN and XHHW which have similar specifications.
Both of these cables are approved up to 600V for the power distribution and are generally used for the purpose of constructing industrial, commercial and residential wiring.
THHN/THWN-2
Between THHN and THWN-2, there is a very slight difference which makes both types electrical wire types almost similar. THHN stands for Thermoplastic High Heat-Resistant Nylon-coated and THWN stands for Thermoplastic Heat and Water-Resistant Nylon-coated.
As defined by the National Electric Code, THHN/ THWN-2 wires are intended to be used in an AC electrical distribution system for general purpose applications. These cables are used for both residential as well as commercial applications in the conduit or cable trays for feeders, services, branch circuits; automotive plants, wind energy, forestry equipment, oil, and petroleum equipment. Apart from these, even engineers use it in control circuits, machine tools, feeders and branch circuits, and other applications as well.
There are two variants 2 variants of conductors: Solid and Stranded
THHN THWN Copper vs. Aluminum
The conductor used in these cables is either Aluminum or Copper. Either way, it has a PVC insulation with a Nylon jacket for further protection from damages such as oil, grease, and other chemicals along with mechanical abrasions.
The copper conductor, in order to remove the internal stress and strengthen the material, undergoes through full annealing process, which turns it into the stranded or bare structure according to ASTM (American Standard for Testing and Materials) B3 and B8 with conductors ranging from 3 to 4 and strands between 7 to 19. It also consists of PVC insulation as per ICEA Method 4 color code with Polyamide-Nylon jacket, which is flame retardant.
Whereas the cable containing aluminum conductor, has compact soft drawn 8000 series aluminum, with Class B stranding with polyvinyl chloride PVC insulation and nylon jacket for abrasion, heat, sunlight, and moisture resistant with reduced coefficient of friction.
Properties Of THHN Wire
THHN/THWN can function in a wide range of temperatures, but the maximum operating temperature is 90° degree Celsius in dry locations in THHN and the temperature of the conductor is not supposed to exceed 90° C or not to exceed 75° C for wet locations such as oil or coolant, well on the other side the maximum voltage capacity rating is 600V olts starting from 110 Volts.
THHN/THWN-2 wire comes in standard American Wire Gauge sizes ranging from 10 AWG to 4/0 AWG in general and sizes from 250MCM to 1000MCM. The insulation of the cable is shared by the nylon jacket for protection as it provides cut protection, which is greatly reduced in its absence.
Since the cable has such a wide range of applications, it is designed to ensure the transmission of current, stability of function and secure installation.
Common Features of THHN/THWN-2
- With thinner PVC, the wire/cable does not consume much space in the installation area
- Wire insulation is Thermoplastic
- Minimum installation temperature is -10°C
- Emergency Overload Temperature is 105°C
- Short Circuit Temperature is 150°C (Max)
XHHW/XHHW-2
Similar to that of THHN/THWN-2, XHHW is Cross-linked High Heat Water-Resistant. XHHW-2 is the upgraded version of XHHW. It is used in residential, commercial and industrial building wiring. Apart from that, it's also used in the feeder, raceways and circuit wiring.
This cable consists of Aluminum and Copper conductors which are in solid or stranded form.
The Copper conductor is as per ASTM B3 and B8 for annealed and stranded copper wires respectively.
The temperature rating that these XHHW/XHHW-2 can withstand is 90°C for both wet and dry atmospheric conditions with the voltage capacity up to 600V as per the National Electric Code. Insulation is Cross-linked Polyethylene (XLPE), a flame retardant as per UL - 44, the protection is assured from most of the damages.
In an Aluminum based conductor, it is compact soft drawn bare 8000 series with class B stranding per ASTM with the same XLPE insulation.
Previously, XHHW had a temperature rating of 75°C in wet environments. Thus, the new XHHW is more reliable with higher temperature capacity.
XHHW/XHHW-2 wire comes in standard American Wire Gauge sizes ranging from 8 AWG to 4/0 AWG in general and sizes from 250MCM to 1000MCM, according to copper or aluminum, solid or stranded.
Features of XHHW/XHHW-2
- XHHW/XHHW-2, when compared with THHN/THWN-2, has XLPE insulation rather than PVC. This material is much more resistant to ozone, abrasion, and chemicals
- Wire insulation is Thermoset
- Minimum installation temperature is -40°C
- Emergency Overload Temperature is 130°C
- Short Circuit Temperature is 250°C (Max)
THHN THWN VS. XHHW: Choosing the right one
When comparing both types of cable, XHHW is superior to THHN
- The insulation method used in XHHW wire is much better than THHN, as the PVC resistance properties are less advanced compared to XLPE insulation
- The Jacket of the XHHW cable is thicker, resulting in better protection from the environmental factors. However, a thin jacket of THHN cable is great for putting the cable in conduit.
- The size of insulation might not matter when compared to the protection it provides. THHN has thinner insulation and jacket, which results in lower protection. XHHW has higher chances in terms of overall safety.
- In terms of flexibility, XHHW has thicker insulation and its jacket is more flexible compared to THHN. This makes it easy to install.
- THHN wire can experience current leakage, which is rarely seen in XHHW
- XHHW is more expensive than THHN, but totally worth the price due to the safety factors. Its coating is more resistant to chemicals, ozone and abrasion.
While XHHW/ XHHW-2 offers more advantages, THHN/THWN-2 meets the needs of many applications, and is still a popular choice among the customers because of the low budget. Both cables are popular, versatile, and safe to use.
