Module Wiring RE LAB [RE-wrenches]
Pat Kiernan, Eco Electric, Inc.
ecoelec at rof.net
Thu May 18 12:31:08 EDT 2000
<x-flowed>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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>
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