Module Wiring RE LAB [RE-wrenches]
Bob Maynard, Energy Outfitters
bob at energyoutfitters.com
Thu May 18 12:21:36 EDT 2000
<x-flowed>Hi Pat,
I just spoke to Arthur Rudin regarding the labeling. He states that
as of about a month ago, SP75's
started leaving the factory with correct labels (15A), although I
personally haven't seen any yet
come through our warehouse. He further states that all SP75's are
rated for 15A fuses, the old
labeling is incorrect. Think you could convince an inspector? I couldn't.
Bob Maynard
Energy Outfitters
1-800-GO-SOLAR
"Pat Kiernan, Eco Electric, Inc." wrote:
> That's not what I would have expected at all. The last SP75s I installed
> indicated a maximum series fuse of 8 amps. Anyone out there have any
> labeled for 15 amps?
>
> Pat Kiernan
>
> ----- Original Message -----
> From: Bob Ellison, Alternative Energy Systems <ellison at gisco.net>
> To: <RE-wrenches at topica.com>
> Sent: Saturday, May 06, 2000 4:26 PM
> Subject: RE: Module Wiring RE LAB [RE-wrenches]
>
> > Your right I NEVER would have expected this answer.
> > Now I am wondering how hot it has to get to reach the point where "cheese
> > cloth singes".
> > I wonder where this test came from?
> >
> > If you feed it 20 amps can you cook on it?
> >
> > Bob Ellison
> >
> > -----Original Message-----
> > From: Drake Chamberlin, Quicksilver Electrical
> > [mailto:solar at eagle-access.net]
> > Sent: Saturday, May 06, 2000 1:33 PM
> > To: RE-wrenches at topica.com
> > Subject: Re: Module Wiring RE LAB [RE-wrenches]
> >
> > << File: ATT00002.htm >> << File: ATT00005.htm >> Pat,
> >
> > It looks like we have the official word form Siemens concerning the
> > fusing of series sets of modules. The answer may have been a bit
> different
> > from what anyone suspected.
> >
> > According to Arthur Rudin, we can parallel 2 sets of Siemens SP 75s,
> and
> > run the series - parallel set to a 15 amp fuse. Below is his reply.
> >
> >
> ****************************************************************************
> > ***************
> >
> > Hi Drake,
> > You are asking the right questions.
> > The maximum series fuse rating indicated on the module rating label is a
> > result of testing and not a calculation. The rating indicates the modules
> > ability to tolerate reverse current without causing a fire (per UL).
> > Current is fed into the module until the temperature reaches a point where
> > cheese cloth singes. It is the maximum size fuse you can use. A smaller
> > size is acceptable.
> > For example, our SP 75 modules have a maximum series fuse rating of 15
> amps.
> > You can parallel two strings with a single fuse. This is acceptable per
> UL.
> > Your suggested wiring configuration will work well.
> > I hope this information helps.
> >
> > Best regards,
> > Arthur
> >
> >
> ****************************************************************************
> > ***************
> >
> > My next task is to find more about the test. What voltage did it take
> > to force 15 amps backwards through the modules? Can the open circuit
> > voltage from a nominal 24 volt series set really push enough reverse
> current
> > through the modules to cook them?
> >
> > I seem to remember an old "Code Corner" in Home Power where Mr. Wiles
> > indicated that it required a ground fault, on the wire that was used to
> > series the modules, for this to be a problem. Does anyone remember this
> or
> > which issue it was in?
> >
> > If we really can fry modules, we will certainly want to cover our
> > liabilities (asses) by using the fuses. At least, now we can get by with
> > half as many whips as we were using previously. Possibly we could use in
> > line fuses, installed in J-boxes, as the supplementary overcurrent
> > protection required for protection for the modules. .
> >
> > Thanks for "asking the right questions."
> >
> > Drake
> > ----- Original Message -----
> > From: Pat Kiernan
> > To: RE-wrenches at topica.com
> > Sent: Friday, April 28, 2000 3:50 PM
> > Subject: RE: Module Wiring [RE-wrenches]
> >
> >
> >
> > --------------------------------------------------------------------------
> --
> > --
> >
> >
> > Drake,
> >
> > Good point about the wires being cooler when the modules are cooler and
> > output current is higher.
> >
> > I believe that the series overcurrent device requirement for each
> parallel
> > string is a UL 1703 requirement (not NEC). For a Siemens SP75 the maximum
> > fuse is 8 amps (4.8 x 1.25 x 1.25 = 7.5A). This value should be indicated
> on
> > the module label.
> >
> > It sure would be nice to find some way to eliminate the series fuses.
> > Thanks for your effort in pursuing this.
> >
> > Pat
> >
> >
> >
> >
> >
> > Re: RE Lab: Module Wiring [RE-wrenches]Hi Travis,
> >
> > We do need to multiply the module currents by 1.25 twice to get the
> > code required current rating. I inserted the note from Siemens as it was
> > written. The important thrust of the message to me was that we only need
> to
> > follow code, that we don't need extra fuses in the system.
> >
> > Different sets of modules will, of course, require their own
> calculations.
> > Here is an example that I believe is in compliance with both the NEC and
> > Siemens requirements.
> >
> > Eight Siemens SP 75s wired in series-parallel for 24 volts, have a short
> > circuit rating of 19.2 amps (4.8 X 4) . Multiply that times 1.25 twice (to
> > comply with code) and you get 30 amps. A pair of number 10 THWN-2 wires
> > should satisfy any inspector. (* Note: The rating of THWN-2 comes on many
> > THHN conductors).
> >
> > An interesting point here is that if the modules are going to be so cold
> > that they will produce enough extra current that the second 1.25
> > multiplication factor needs to be used, the wire will also be cold, and
> thus
> > its current carrying capacity will be higher.
> >
> > What I understand from the message, from Arthur Rudin of Siemens, is
> that
> > each series set does not require its own fuse. The old code seemed to
> > require a fuse for each series set.
> >
> > The total series - parallel module configuration must be wired so that
> the
> > code required calculations don't show more amperage than the wiring and
> > fuses would be able to handle.
> >
> > Thanks for helping sort out this tangled issue.
> >
> > Drake
> > RE Lab
> > ----- Original Message -----
> > From: Travis Creswell
> > To: RE-wre- at topica.com
> > Sent: Thursday, April 27, 2000 7:07 PM
> > Subject: Re: RE Lab: Module Wiring [RE-wrenches]
> >
> >
> >
> > ------------------------------------------------------------------------
> --
> > ----
> >
> >
> > Drake,
> >
> > What is the Siemens module rating for max series fuse and short circuit
> > current? They must be rated quite differently than the modules that I am
> > used to.
> >
> > Why do you only use 1.25 de-rate instead of1.56?
> > See Table 690-7 Page 849 of the 1999 NEC Handbook. In areas where the
> temp
> > can get to -5 F then you need to use 1.25 in addition to the 1.25 de-rate
> > required in 690.8(a)(1). 1.25x.125=1.56
> >
> > Some of the modules here at my shop are rated as follows
> > Max Series Fuse Isc x 1.56 de-rate
> > AP1206 10 Amps 7.7 12
> > US64 8 amps 5.1 7.96
> > BP585 8 Amps 5.0 7.8 (I
> > think, they are on the roof and I don't feel like getting up there right
> > now)
> >
> >
> > >From the above numbers it looks like the Astro Power 120 has a problem
> > but the ones I've installed over the last year have upped the max series
> > fuse rating to 15 amps. What this means to me is that I can only series
> > the above modules. We installed some Solarex MSX 60's recently and I think
> > they had a max series fuse rating of 20 amps which I thought I was very
> > high. Can someone check out a MSX60 and reply with that info?
> >
> > If you are allowed to use the 1.25 de-rate it still means that you can
> > only parallel two modules. Are you implying that you can parallel as many
> > modules as you want? In parallel, as I see it, you are forcing the
> > downstream modules to pass the current from the upstream modules through
> > them.
> >
> > Keep up the hard work on the research you are doing out there.
> >
> > Travis Creswell
> > Ozark Solar
> > ----------
> > From: Drake Chamberlin - Electrical Energy <sol- at eagle-access.net>
> > To: RE-wre- at topica.com
> > Subject: RE Lab: Module Wiring [RE-wrenches]
> > Date: Thu, Apr 27, 2000, 6:07 PM
> >
> >
> >
> > Hi Wrenches,
> >
> > I went through the Siemens Web site to get answers to the question
> of
> > daisy chaining series strings of modules. It appears that there is no fuse
> > required between the Series sets anymore.
> >
> > Below is the response from Arthur Rudin of Siemens concerning my
> > question.
> >
> >
> >
> ****************************************************************************
> > *****************
> >
> > Hi Drake,
> > Sorry for the delay in this response. I have been travelling and did
> > not
> > have access to my e-mail. The NEC does require a fuse for each
> source
> > circuit. Modules or strings can be wired in parallel as long as the
> > total
> > short circuit current x 1.25 does not exceed the series fuse rating
> of
> > the
> > module. This is explained in article 690 of the NEC and the NEC
> > handbook.
> > You can check your library for this information.
> >
> > Best regards,
> > Arthur
> >
> >
> ****************************************************************************
> > *************
> > Siemens apparently has no other requirement for their module wiring
> > than the NEC specifications.
> >
> > So if Siemens is going to let us meet the Code requirements for
> module
> > wiring, without using extra fuses between the series pairs, we are safe
> > daisy chaining strings of Siemens modules, and then going to one
> overcurrent
> > device.
> >
> > We can omit those pesky fuses between series strings of modules.
> There
> > is no need for multiple whips to combiner boxes, with all the terminal
> > strips, etc. This is the new Code, and it is a lot easier than the last.
> >
> >
> >
> >
> > Drake
> >
> >
> RE
> > Lab
> >
> >
> >
> ****************************************************************************
> > *******************
> >
> > Pat Kiernan
> > Eco Electric, Inc.
> > PO Box 2389
> > Basalt, CO 81621-2389
> > tel/fax (970) 927-9270
> > e-mail: ecoelec at rof.net
> >
> >
> > --------------------------------------------------------------------------
> --
> > --
> >
> >
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