Flexible Cables: Important Safety Issue [RE-wrenches]

Dean T. Newberry deant at dcn.org
Thu Aug 26 09:18:15 PDT 2004


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Hi Matt,
    The guys with the Black helicopters don't give a rats ass about you 
burning down customers houses or businesses. They care a lot about Radio 
Frequency Interference (RFI) from your PV system, the recommendation is 
to use FCC compliant inverters and put the DC leads from the roof to the 
inverter in EMT.
    I agree with JW's general principle that wire termination methods 
appropriate for the wire and fitting need to be used.

cul  deant

Matt Tritt wrote:

> 
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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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