mstrlucky74
Senior Member
- Location
- NJ
I often see in the spec any vertical run over 50' needs to be XHHW. Why is that?
XHHW Vertical Runs
- Thread starter mstrlucky74
- Start date
- Status
- Location
- Massachusetts
The following is a guess.
XHHW is a much tougher insulation than THHN, longer vertical runs need to have a way to secure them. Perhaps the idea is that the XHHW deals with being secured better than THHN.
Beyond that I got nothing.
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
The following is a guess.
XHHW is a much tougher insulation than THHN, longer vertical runs need to have a way to secure them. Perhaps the idea is that the XHHW deals with being secured better than THHN.
Beyond that I got nothing.
Sounds like a very sound supposition to me. EE's have little idiosyncrasies. It is also common for me to see them require XHHW for the secondaries, but THWN/THHN for any other feeders.
- Location
- Massachusetts
Yeah, and it is awesome us electricians do not. :angel:
Wow, that is an odd one. :huh:
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
Agreed, but I am sure many people who have worked in different areas through their life see that oddities are often reproduced locally. I believe there are three EE's in my area who spec this, whereas in my past life I never saw it.
- Location
- Massachusetts
I agree.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Sometimes I like to hide in the middle of a big book spec, that the electrician shall provide 1 dozen donuts and coffee for the EE at every site meeting.
- Location
- Massachusetts
lielec11
Senior Member
- Location
- Charlotte, NC
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Most likely it's because of how the insulation is made. Thermoplastic insulation like THHN (Thermoplastic High Heat Nylon jacketed) is basically liquid PVC extruded around the wire as it passes through a die, then into an oven to be "set" by heat into a more solid form. But really, it can still flow a little over time and especially when heated. So in a vertical run, the heat in the raceway will rise and may cause the upper parts of the insulation to thin out. The "X" in XHHW stands for Cross linked Polyethylene (XLPE) insulation instead of Thermoplastic. XLPE is essentially heat shrink tubing, so it starts out at a particular size, is heated and expanded, then the wire is inserted and when heated again, returns to its original size. So it is not only a more uniform insulation thickness, it does not "flow" when heated, it actually gets tighter on the cable. That would make it better for a long vertical run.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
We use Sim-pull XHHW for vertical risers. When held side by side with Sim-pull THHN they appear to be almost identical.
brantmacga
Señor Member
- Location
- Georgia
- Occupation
- Former Child
I see that on aluminum specs regularly but not really on copper.
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brantmacga
Señor Member
- Location
- Georgia
- Occupation
- Former Child
JFletcher
Senior Member
- Location
- Williamsburg, VA
Is this copper vs aluminum? Aluminum of the same kcmil as copper can be run a longer distance vertically before conductor support becomes necessary.
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