XHHW-2 vs THHN Wire

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stuartdmc

Senior Member
Location
Newport Beach, Irvine, CA
We're being asked By the Engineer on our project to install in all of our exterior conduits including the service riser XHHW-2 copper wire. This is unlike anything we've done in our area.
The project is in Hollywood, Southern California (Never to Hot and Never to Cold).

Ive looked up the properties of THHN wire which seems to meet the application and requirements for exterior installation of feeders.

How do I get the Engineer to see my point and change his plans?


Thanks.
Stuart
 
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Hv&Lv

Senior Member
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Occupation
Engineer/Technician
stuartdmc said:
We're being asked By the Engineer on our project to install in all of our exterior conduits including the service riser XHHW-2 copper wire. This is unlike anything we've done in our area.
The project is in Hollywood, Southern California (Never to Hot and Never to Cold).

Ive looked up the properties of THHN wire which seems to meet the application and requirements for exterior installation of feeders.

How do I get the Engineer to see my point and change his plans?


Thanks.
Stuart
Click to expand...

don't show him this..http://express-press-release.net/59...ny Electrical Contractors Verse THHN Wire.php
 
kwired

kwired

Electron manager
Location
NE Nebraska
I don't think it was specified because of temperature - they are both 90 degree conductors.

XHHW insulation is tougher material than the plastic that THHN is made of. It will withstand more abuse during installation. You may want to find out the reasoning why it was preferred by the designer.

THHN is a dry location only conductor. THWN can be used wet or dry. Most of the thermoplastic insulated conductors commonly available are dual rated THHN/THWN/TWWN-2.
 
kwired

kwired

Electron manager
Location
NE Nebraska
I have used a lot of XHHW aluminum conductor and have noticed it usually seems easier to install, but some of that could be the fact that aluminum is not as heavy as copper.
 
don_resqcapt19

don_resqcapt19

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Staff member
Location
Illinois
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retired electrician
From the link in post #3:
XHHW has better current carrying capacity giving it the ability to withstand meltdown better ...
Click to expand...
How does it have a better current carrying capacity?
 
kwired

kwired

Electron manager
Location
NE Nebraska
don_resqcapt19 said:
From the link in post #3:

How does it have a better current carrying capacity?
Click to expand...

Hv&Lv said:
Higher melting temperatures
Click to expand...

Why are both listed in 90 degree column of 310.16 if they are not the same?

It may have higher melting temp, but will not be subject to higher temp if installed per same ampacity rating, I guess it will just stand up longer when there is misuse or a failure.
 
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Hv&Lv

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kwired said:
Why are both listed in 90 degree column of 310.16 if they are not the same?

It may have higher melting temp, but will not be subject to higher temp if installed per same ampacity rating, I guess it will just stand up longer when there is misuse or a failure.
Click to expand...

It (will, may, could) be of value when using 110(14)(C) for derating conductors passing through different ambient temperatures. ;)

Here is some more information:http://electriciantraining.tpub.com/14176/css/14176_23.htm
 
Dennis Alwon

Dennis Alwon

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Chapel Hill, NC
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kwired said:
Unless the conductor is specifically marked 105?C or 125?C or whatever temp we have to go by 90?C rating don't we?
Click to expand...

I believe you can use any rating that is pertinent but the final ocpd cannot be more than the weakest link-- usually the terminals.
 
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Hv&Lv

Senior Member
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kwired said:
Unless the conductor is specifically marked 105?C or 125?C or whatever temp we have to go by 90?C rating don't we?
Click to expand...

I found this clicking through the Southwire site from the thread going on now about romex. It is an example that makes more sense than I ever could...:D http://www.southwire.com/support/TempRatingsGiveHigherAmpacityLowerCost.htm

You should check out all the stuff on here... Wasn't someone looking for estimating calculators earlier? http://www.southwire.com/commercial/calculators.htm
 
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kwired

kwired

Electron manager
Location
NE Nebraska
Dennis Alwon said:
I believe you can use any rating that is pertinent but the final ocpd cannot be more than the weakest link-- usually the terminals.
Click to expand...
I understand that, but for ambient temperature derating where do we go to find higher than 90?C conductor ampacity?

Most of time when a conductor is marked higher than 90?C we use it for places where ambient is expected to be higher than 90?, like luminaire supply leads, heating element leads, and things like that.
 
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Hv&Lv

Senior Member
Location
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kwired said:
I understand that, but for ambient temperature derating where do we go to find higher than 90?C conductor ampacity?

Most of time when a conductor is marked higher than 90?C we use it for places where ambient is expected to be higher than 90?, like luminaire supply leads, heating element leads, and things like that.
Click to expand...

310.10 310.11 table 310.13(A) Some there have a "2" footnote to go up to 200-250?C
 
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