Flexible Cables: Important Safety Issue [RE-wrenches]

Kurt Nelson sunwise at cheqnet.net
Thu Aug 26 19:34:53 PDT 2004


 

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Hey Matt,

I have not yet read all the posts on this topic, but let me quickly say
two things.  First, I thought JW was commenting on both crimped
connections and connections under a screw.

Second, I have always placed two dabs of No-Ox on at such connections,
one little line along the threads of the screw and another big dab at
the front, compression end of the screw.

I was told that the proper way to tighten these was to reef on the
t-handled allen wrench, but then back off and re-tighten, repeating a
few times.  The last time the screw is tightened there is no additional
compression noticed at the tool and it is not necessary to over tighten.

Kurt Nelson


-----Original Message-----
From: Matt Tritt [mailto:solarone at charter.net] 
Sent: Thursday, August 26, 2004 11:10 AM
To: RE-wrenches at topica.com
Subject: Re: Flexible Cables: Important Safety Issue [RE-wrenches]

 

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  Kurt,

  Even though I find it gratifying to solder cable lugs, the real
subject of
J. Wiles ridiculous suggestion/RULE  is the wire or cable that is
terminated
under a screw or clamp. His "concern" for this connection is that the
fine
wire strands will somehow break in the process of tightening the screw
(or
that it will just keep compressing after it has been completely
compressed
to begin with) resulting in reduced current carrying ability; hence my
tinned cable end reference. See Don's comments on tightening the screw
after
inserting the cable. Better yet, go back to the original message
conduited
through A. Sindelar if you really feel like getting steamed!

  Wiles makes a comment about a "recent problem" with a "large PV
system"
resulting from a loose connection that had been "re-torqued" a short
time
before the Problem occured. The thing that is the biggest pisser about
Wiles
and his cohorts of the meddling persuasion is that this ambigous
"problem"
occurance is turning into a new (and preposterous) rule that will effect
a
huge portion of the industry, from module and inverter manufacturers
clear
down to the guys in the field, and like Bob-O says; the result will be
higher prices for all.


  I completely agree with you about Bob-O; I sure hope the men in the
(UL
approved) black helicopters don't whisk him away in the night!

  Matt T
  ----- Original Message ----- 
  From: "Kurt Nelson" <sunwise at cheqnet.net>
  To: <RE-wrenches at topica.com>
  Sent: Thursday, August 26, 2004 6:50 AM
  Subject: RE: Flexible Cables: Important Safety Issue [RE-wrenches]




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  Hey Bob-O,

  Regarding crimp/solder lugs, I used to do a "primitive" crimp on the
  lugs and then heat the lug and fill with solder.  I've heard that a
  properly crimped connection actually has less resistance than a
soldered
  one (maybe those solder'ers aren't also crimping?).  A couple years
ago
  I bought the big/proper crimping tool.  It is really quick and easy.
  Yet I often walk away from a job thinking that maybe I should have
added
  solder to the lug, to make it a permanent connection.

  All that said, What I really wanted to say was that when it comes to
  these Wrenches posts, and having recently been watching some of the
  Olympics, I am a big fan of Bob-O's style and form.

  Kurt Nelson
  SOLutions

  -----Original Message-----
  From: Bob-O Schultze, Electron Connection
  [mailto:econnect at snowcrest.net]
  Sent: Wednesday, August 25, 2004 10:29 AM
  To: RE-wrenches at topica.com
  Subject: Re: Flexible Cables: Important Safety Issue [RE-wrenches]



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  Well, that's old JW all over isn't it? Find a situation that could be
  a problem or that is very, very rarely a problem and make Mt Everest
  out of a molehill. Since day one of his inputs to the RE industry
  everything he suggests or opines that UL/NEC requires raises the cost
  of a PV system. EVERYTHING! Ever notice that? This man comes to us
  from the nuke industry. I find it damn hard not to question his
  motives. He's kind of a Swift Boat PV Opinionater for Arcane Stuff,
  ain't he?
  Jesus H. Christ!


  >  Oh my God.
  >
  >   This isn't April 1st is it?
  >
  >   So now all those inverters that we've been putting in with "fine
  stranded
  >wire" for the past 20 years are going to have to have their cables
  removed
  >and exchanged because "there have been problems"? What, fires?
  Explosions?
  >Electrocutions? Befuddled inspectors?
  >
  >   I have to say that in all the years I've been working on
  battery-based
  >inverters, the ONLY connection problems I have observed  have ONLY
been
  >those that had stiffy wire for inverter cables! There is so much
  potential
  >for tension-caused breakage with this method, so many (virtually)
  impossible
  >wire bends and seeming non-compatablity with all the commonly used,
  tried
  >and true connection components, I just can't bel;ieve that this can
be
  for
  >real.
  >
  >   If this such a huge problem, why not simply tin the wire ends?! UL
  indeed.
  >
  >   Matt T
  >   ----- Original Message -----
  >   From: "Allan Sindelar" <allan at positiveenergysolar.com>
  >   To: "New wrenches posting" <RE-wrenches at topica.com>
  >   Sent: Tuesday, August 24, 2004 3:35 PM
  >   Subject: Fw: Flexible Cables: Important Safety Issue [RE-wrenches]
  >  Wrenches,
  >   Forwarded to this list at the request of John Wiles
  >
  >   ----- Original Message -----
  >   From: "John Wiles" <jwiles at nmsu.edu>
  >   Sent: Tuesday, August 24, 2004 3:50 PM
  >   Subject: Flexible Cables
  >
  >
  >   Flexible, Fine-Stranded Cables: Incompatibilities with Set-Screw
  >Mechanical
  >   Terminals and Lugs
  >
  >   Reports have been received over the last several years about
  field-made
  >   connections that have failed when flexible, fine-stranded cables
  have been
  >   used with mechanical terminals or lugs that use a set screw to
hold
  the
  >wire
  >   in the terminal.
  >
  >   These terminals are found on nearly all circuit breakers (except
  those
  >with
  >   stud-type terminals), fuse holders, disconnects, PV inverters,
  charge
  >   controllers, power distribution blocks, some PV modules, and many
  other
  >   types of electrical equipment.
  >
  >   Fine-stranded conductors and cables are considered as those cables
  having
  >   stranding more numerous than Class B or C stranding. Class B
  stranding
  >(the
  >   most common) will normally have 7 strands of wire per conductor in
  sizes
  >   18-2 AWG, 19 strands in sizes 1-4/0 AWG, and 37 strands in sizes
  250-500
  >   kcmil. Conductors having more strands than these are widely
  available and
  >   are in different classes such as K and M used for portable power
  cords and
  >   welding cables. Commonly used building-wire cables such as USE,
THW,
  RHW,
  >   THHN and the like are most commonly available with Class B
  stranding, but
  >   are also readily available with higher stranding. Fine-stranded
  cables are
  >   frequently used by PV installers to ease installation and are used
  in PV
  >   systems for battery cables, power conductors to large
  utility-interactive
  >   inverters and elsewhere.
  >
  >   Some modules are supplied with fine-stranded interconnecting
cables
  with
  >   attached connectors. While these crimped-on connectors listed with
  the
  >   module are suitable for use with the fine-stranded conductors, an
  >   end-of-string conductor with mating connector may also be supplied
  with
  >the
  >   fine-stranded conductor ,and the unterminated end of that
conductor
  will
  >not
  >   be compatible with mechanical terminals.
  >
  >   According to UL Standard 486 A-B, a terminal/lug/connector must be
  listed
  >   and marked for use with conductors stranded in other than Class B
  and C.
  >   With no marking or factory literature/instructions to the
contrary,
  the
  >   terminal may only be used with conductors with the most common
Class
  B and
  >C
  >   stranded conductors. They are not suitable and should not be used
  with
  >   fine-stranded cables. UL engineers have said that few (if any) of
  the
  >normal
  >   screw-type mechanical terminals that the PV industry commonly uses
  have
  >been
  >   listed for use with fine stranded wires. The terminal must be
marked
  or
  >   labeled specifically for use with fine-stranded conductors.
  >
  >   UL suggests two problems, both of which have been experienced in
PV
  >systems.
  >   First, the turning screw tends to break the fine wire strands,
  reducing
  >the
  >   amount of copper available to meet the listed ampacity. Secondly,
  the
  >   initial torque setting does not hold and the fine strands continue
  to
  >   compress after the initial tightening. Even after subsequent
  retorquing,
  >the
  >   connection may still loosen. The loosening connection creates a
  >   higher-than-normal resistance connection that heats and may
  eventually
  >fail.
  >   Recent examples of failed mechanical terminals from a large PV
  system have
  >   been found. The terminal had been torqued properly less than three
  months
  >   before the failure.
  >
  >   Solutions
  >
  >   All electrical equipment listed to UL Standards has:
  >
  >   . Terminals rated for the required current and sized to accept the
  proper
  >   conductors
  >
  >   . Sufficient wire bending space to accommodate the Class B
stranded
  >   conductors in a manner that meets the wire bending requirements of
  the NEC
  >
  >   . Provisions to accept the appropriate conduit size for these
  conductors
  >   where conduit is required.
  >
  >   It is therefore unnecessary to use the fine-stranded cables except
  >possibly
  >   when dealing with conductors 4/0 AWG and larger.
  >
  >   In those cases where a fine-stranded cable must be used, a few
  >manufacturers
  >   make a limited number of crimp-on compression lugs in various
sizes
  that
  >are
  >   suitable for use with fine-stranded cables.
  >
  >   Factory-supplied markings and literature indicate which lugs are
  suitable.
  >   An example is the ILSCO FE series of lugs in sizes 2/0 AWG and
  larger.
  >   Burndy makes a YA series of lugs in sizes 14 AWG and up. In both
  cases the
  >   lugs are solid copper. It should be emphasized: Most crimp-on lugs
  are not
  >   listed for use with fine-stranded wire. Where the crimp-on
  compression
  >lugs
  >   can be used, they must be installed using the tools recommended by
  the
  >   manufacturer and, of course, they must be attached to a stud with
a
  nut
  >and
  >   washer.
  >
  >   Burndy and others make pin adapters (a.k.a. pigtail adapters) that
  can be
  >   crimped on fine-stranded cables. These pin adapters provide a
  protruding
  >pin
  >   that can be inserted into a standard screw-type mechanical
  connector.
  >Again,
  >   not all pin adapters/pigtail adapters are listed for use with
  >fine-stranded
  >   conductors; some are intended for use with aluminum wire and
others
  >provide
  >   only a conversion to a smaller AWG size for B Class conductor.
  >
  >   It is suggested that the use of fine-stranded conductors be
avoided
  >wherever
  >   possible. Where such cables must be used, they should only be
  terminated
  >   with the appropriate connectors/lugs. Previously installed systems
  should
  >be
  >   revisited and the cables replaced where possible or terminated
  properly.
  >
  >   John Wiles SWTDI/NMSU jwiles at nmsu.edu 505-646-6105
  >
  >   > If I can provide further information, please do not hesitate to
  call,
  >   > e-mail or fax me.
  >   >
  >   > John
  >   >
  >   > John C. Wiles,  Program Manager
  >   > Southwest Technology Development Institute, New Mexico State
  University
  >   > 505-646-6105      505-646-3841 (FAX)   http://www.NMSU.Edu/~tdi
  >   > SWTDI/NMSU
  >   > Corner Research Drive and Sam Steel Way
  >   > Box 30001/MSC 3 SOLAR
  >   > Las Cruces, NM 88003-8001
  >

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