Opinion on higher quality install

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farmaped

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Engineer
Which of these installations would you prefer, based on installation Cost and overall project Quality (Longevity).
Industrial setting, 200Amp 3P 480V feeders. Utilizing Under-Floor Trenches for the wire runs. Trenches are not subject to traffic / damage, but they do fill with water occasionally.
1. EMT with THWN-2 Conductors
2. PVC Jacketed Aluminum Armor MC Cable with XHHW-2 Conductors
3. PVC Jacketed Glavanized Steel Armor MC Cable with XHHW-2 Conductors
Thanks in advance for your thoughts.
 
I would stay away from EMT and THWN in an area that might get submerged.

If the run is not subject to physical damage I would consider PVC with XHHW-2 conductors.
 
farmaped said:
Which of these installations would you prefer, based on installation Cost and overall project Quality (Longevity).
Industrial setting, 200Amp 3P 480V feeders. Utilizing Under-Floor Trenches for the wire runs. Trenches are not subject to traffic / damage, but they do fill with water occasionally.
1. EMT with THWN-2 Conductors
2. PVC Jacketed Aluminum Armor MC Cable with XHHW-2 Conductors
3. PVC Jacketed Glavanized Steel Armor MC Cable with XHHW-2 Conductors
Thanks in advance for your thoughts.
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Jacketed CLX. Armor is useless when the PVC is punctured.

Tray cable would also work since it is in a trench and there seem to be no need for physical protection.
 
iwire said:
I would stay away from EMT and THWN in an area that might get submerged.

If the run is not subject to physical damage I would consider PVC with XHHW-2 conductors.
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Just wondering why you chose xhhw-2? Is it a better choice for wet apps?
 
SmithBuilt said:
Just wondering why you chose xhhw-2? Is it a better choice for wet apps?
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I have used both THWN and XHHW and there is no doubt in my mind that XHHW is tougher installation and if left up to me I will always choose it for flooded locations.

For example look at insulation thickness

1/0 XHHW-2 insulation thickness is 55 mils

http://www.southwire.com/ProductCatalog/proddetail.jsp?htmlpreview=true&token=5&desc=CU-XHHW

1/0 THHN-2 insulation thickness is 50 mils


http://www.southwire.com/ProductCatalog/proddetail.jsp?htmlpreview=true&token=1&desc=CU-THHN
 
iwire said:
I have used both THWN and XHHW and there is no doubt in my mind that XHHW is tougher installation and if left up to me I will always choose it for flooded locations.

For example look at insulation thickness

1/0 XHHW-2 insulation thickness is 55 mils

http://www.southwire.com/ProductCatalog/proddetail.jsp?htmlpreview=true&token=5&desc=CU-XHHW

1/0 THHN-2 insulation thickness is 50 mils


http://www.southwire.com/ProductCatalog/proddetail.jsp?htmlpreview=true&token=1&desc=CU-THHN
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The insulation thickness is not necessarily a sign of better suitability for water immersion. The thickness has to do with accomplishing the necessary dielectric strength for insulation to the given voltage level. So in that sense cross-linked-polyethylene is inferior to the polyvinyl-chloride insulation since it needs a greater thickness to accomplish the same insulation level.

All polymers are permeable to liquids. Some to a lesser and some to a greater degree. That, along with the thickness and the other chemicals present in the water will determine the first-to-fail timeline. In high voltage applications there are additional factors play major role that does not exist at the <600VAC level. DC is yet another issue.
 
MC HL is what we use all over the north slope of Alaska, out in the oil patch. Here is a link that may help in determining something for you.
 
Hey cow, listen up. That PVC coated rigid is cost prohibitive.

Don't like that?

I'll send the "caribou barbie" out to talk to you....
 
weressl said:
The insulation thickness is not necessarily a sign of better suitability for water immersion. The thickness has to do with accomplishing the necessary dielectric strength for insulation to the given voltage level. So in that sense cross-linked-polyethylene is inferior to the polyvinyl-chloride insulation since it needs a greater thickness to accomplish the same insulation level.

All polymers are permeable to liquids. Some to a lesser and some to a greater degree. That, along with the thickness and the other chemicals present in the water will determine the first-to-fail timeline. In high voltage applications there are additional factors play major role that does not exist at the <600VAC level. DC is yet another issue.
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Ok lets just say that XHHW2 can take more of a beating with the thicker jacket
 
weressl said:
The insulation thickness is not necessarily a sign of better suitability for water immersion.
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Look beyond the texts and into the field.

IMO it provides more protection from damage during installation. It is damage to THWN during the installation that causes the failures in water logged conduits.
 
The least expensive is THHN or THWN, the next is XHHW and the most expensive is RHH/RHW.

THHN/THWN is PVC insulation and it has a nylon sheath. THHN is only rated for 90 deg in dry locations. THWN is rated for 90 deg C in wet or dry. PVC also has a short circuit-temperature limitation of 150 deg C. A huge disadvantage of PVC is that it cannot be bent/installed at temperatures below -10 DegC/+14 degF.

XHHW is an XLPE insulation. It is rated for 90 deg C wet or dry locations. It is harder to work with than THWN but it is tougher, possesses good compression and is flexible over a wide range of temperatures. It is highly resistant to ozone and stress cracking. It is however susceptible to the growth of water trees.

RHW can be found in either XLPE or EPR. EPR is not as tough as XLPE but is more flexible. EPR is flammable, so they are provided with a jacket to make them flame retardant and for mechanical protection. EPR is very resistant to the growth of water trees, therefore would be an improvement in UG installations. XLPE is the same as XHHW but the is much thicker on RHW therefore better in a more abusive type environment. RHW can also be rated for direct buried installs.

IMO- in an industrial environment, all three types have their place. THWN is only good for general lighting circuits. XHHW can be used for large feeders above ground in conduit and in cable tray. RHW w/ EPR insulation is better and can be used AG and should be the only choice for use in UG due to conduits usually being full of water, and to motor or vibrating loads due to flexible properties.
 
jrannis said:
Ok lets just say that XHHW2 can take more of a beating with the thicker jacket
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For impact, bending and abrasion resistance - again - measurable parameters of hardness, elasticity and pliability would be the determining factor.

I think we established in another post that the nylon jacket on the THWN often gets damaged during pull. This damage is equivalent to the abrasion scuffmarks that can be seen on the walls of XHHW. It was also established - to my surprise - that the nylon jacket is not part of the insulation. The thorn nylon jacket therefore is not necessarily indicative of more severe damage.

If someone can show me collected data and numbers that show that XHHW can take 'more beating' then I yield. Until then this just remains another myth, unsupproted by data.

Mind you that I will specify XHHW forever over THHN, but for an enetirely different reason that was not cited here, nor is it the subject of discussion.
 
kingpb said:
The least expensive is THHN or THWN, the next is XHHW and the most expensive is RHH/RHW.

THHN/THWN is PVC insulation and it has a nylon sheath. THHN is only rated for 90 deg in dry locations. THWN is rated for 90 deg C in wet or dry. PVC also has a short circuit-temperature limitation of 150 deg C. A huge disadvantage of PVC is that it cannot be bent/installed at temperatures below -10 DegC/+14 degF.

XHHW is an XLPE insulation. It is rated for 90 deg C wet or dry locations. It is harder to work with than THWN but it is tougher, possesses good compression and is flexible over a wide range of temperatures. It is highly resistant to ozone and stress cracking. It is however susceptible to the growth of water trees.

RHW can be found in either XLPE or EPR. EPR is not as tough as XLPE but is more flexible. EPR is flammable, so they are provided with a jacket to make them flame retardant and for mechanical protection. EPR is very resistant to the growth of water trees, therefore would be an improvement in UG installations. XLPE is the same as XHHW but the is much thicker on RHW therefore better in a more abusive type environment. RHW can also be rated for direct buried installs.

IMO- in an industrial environment, all three types have their place. THWN is only good for general lighting circuits. XHHW can be used for large feeders above ground in conduit and in cable tray. RHW w/ EPR insulation is better and can be used AG and should be the only choice for use in UG due to conduits usually being full of water, and to motor or vibrating loads due to flexible properties.
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'Water trees' have not been observed in low woltage installation it is only a problem in MV applications. It also have to do with the purity of the compounding as 'trees' grow around impurites and nodules of incomplete reaction rather than due to the material itself.

Certainly your comments have more merit on actual physical parameters comparison. As I said earlier all polymers are permeable and failure is just a matter of time difference between one and the other.
 
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