New wire for array wiring? [RE-wrenches]

Allan Sindelar allan at positiveenergysolar.com
Wed Dec 15 08:45:08 PST 2004


 

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Re: Fw: new wire for array wiring? [RE-wrenches]----- Original Message ----- 
Much to my suprise, we concluded that XHHW-2 is rated for exposure to=20
the sun.

Maybe a commentary from John Wiles would be useful at this time.

cul deant

From: John Wiles 
To: Allan Sindelar 
Sent: Wednesday, December 15, 2004 9:31 AM

Thanks for the forward:  Here is a non-answer.


The October 2003 UL Wire and Cable Marking Guide indicates that XHHW and XHHW-2 as single wires may be sunlight resistant if so marked.


I have seen cable manufacturers advertisements that say that their XHHW-2 single conductors are sunlight resistant and those conductors have been marked.  Although available as single conductors, much of the XHHW-2 conductors are made into multi-conductor service entrance cables (type SE) with pretty large conductors that are not suitable for PV module interconnections.


This UL Guide also indicates that SE, USE and USE-2 cables are sunlight resistant and do not have to be marked.  According to the cable manufacturers, this also applies to SE, USE, and USE-2 single conductor wires.


In a similar vein, BP Solar is attaching RHW-2 conductors (that are marked sunlight resistant) to modules.  UL is listing these modules, but does admit that the RHW-2 conductors do not pass the UL USE Crush Test.  Some inspectors question the use of this cable which is not one of the conductors listed in NEC Section 690.31, but accept it based on the fact that it is attached to a listed module.


We also have THHN/THWN-2 conductors marked sunlight resistant available in the market place further complicating the issue.


However, PV modules are expected to be producing dangerous amounts of electrical energy for 40-50 years are more.  The NEC was written with this in mind.  The SE and USE cables required in NEC Section 690.31 are some the toughest cables that are commonly available.  This is particularly true when they are made of cross-linked polyethylene (XLP/XLPE).  In the exposed locations where these cables are allowed, they must be tough to resist wind and weather loadings as well as sunlight.


The NEC currently (and in the 2005 NEC) allows USE, USE-2, and SE cables/conductors.  UF may be used where marked sunlight resistant.  USE and UF should be used with caution as many of them have only a 75°C wet rating and not the desired and usually required 90°C wet rating.


As an additional note, UL is working on a standard for a PV cable that will meet the "intent" of the new Section 690.35 in the 2005 NEC.  This new section will permit (not require) the installation of ungrounded PV arrays.  That cable will be sunlight resistant, pass the USE crush test and have a jacket that is twice the thickness of the current USE conductors.  See Code Corner in the next issue of Home Power magazine for details.


John Wiles  505-646-6105  jwiles at nmsu.edu


>From original post:


  ARTICLE 338 Service-Entrance Cable: Types SE and USE
  I. General
  338.1 Scope.
  This article covers the use, installation, and construction=20
  specifications of service-entrance cable.
  According to the 2001 UL Electrical Construction Materials Directory,=20
  category TXKT (service cable) and category TYLZ (service-entrance cable=20
  rated 600 volts) are listed in sizes 14 AWG and larger for copper and 12=20
  AWG and larger for aluminum or copper-clad aluminum. Type SE cable=20
  contains Types RHW, RHW=AD2, XHHW, XHHW=AD2, THWN, or THWN=AD2 conductors.=
  =20
  Type USE cable contains conductors with insulation equivalent to RHW or=20
  XHHW. _Type USE-2 contains insulation equivalent to RHW-2 or XHHW-2 and=20
  is rated 90=B0C wet or dry. _
  The type designation of the conductors may be marked on the surface of=20
  the cable. When used, this marking indicates the temperature rating for=20
  the cable corresponding to the temperature rating of the conductors.=20
  When this marking does not appear, the temperature rating of the cable=20
  is 75=B0C. The cables are designated as Type SE, Type USE or USE-2, and=20
  submersible water pump cable.
  Type SE, cable for aboveground installation. Both the individual=20
  insulated conductors and the outer jacket or finish of Type SE are=20
  suitable for use where exposed to sun.
  Type USE or USE-2, cable for underground installation, including burial=20
  directly in the earth. Cable in sizes 4/0 AWG and smaller and having all=20
  conductors insulated is suitable for all of the underground uses for=20
  which Type UF cable is permitted by the Code. Types USE and USE-2 are=20
  not suitable for use in premises or above ground except to terminate at=20
  the service equipment or metering equipment. _Both the insulation and=20
  the outer covering, when used on single and multiconductor Types USE and=20
  USE-2, are suitable for use where exposed to sun.
  ___________________________________________________________________________=
  _____________


  Matt Lafferty wrote:

  > <>All:
  >
  > XHHW-2 is NOT rated for direct sunlight exposure! I hope it's not being
  > installed outside of a raceway or UV resistant cable sheathing!
  >
  > It is an awsome conductor type for use between the J-Box and the=
   Inverter.
  > I recommend it over THWN-2. Much tougher insulation.

[Non-text portions of this message have been removed]

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