Fw: NEC Article# 690-71(b) (1) & (2) [RE-wrenches]

Don Wallingford quicksilver at eagle-access.net
Fri Mar 24 09:11:33 PST 2000


----- Original Message -----
From: "John Wiles" <jwiles at nmsu.edu>
To: "Don Wallingford" <quicksilver at eagle-access.net>
Cc: <imail at solar.nmsu.edu>; <arosenth at nmsu.edu>; <rfoster at nmsu.edu>;
<gcisnero at nmsu.edu>; "Ward Bower" <wibower at sandia.gov>
Sent: Friday, March 24, 2000 9:59 AM
Subject: Re: NEC Article# 690-71(b) (1) & (2)


> Hi Don:
>
> I had some difficulty reading your e-mail.  It was blank.  Seems like you
> and a few others out there send e-mail in HTML.  Many popular e-mail
> programs like Eudora do not support HTML.  I finally opened your e-mail
> with my web browser, but that technique is not common knowledge.   You
> might want to consider turning off the HTML feature on your e-mail
program.
>
> Glad to hear the Wrench list is up and working.  Feel free to share the
> following.
>
> There is no intent in the NEC to prohibit battery systems in dwellings at
> any voltage. There are PV-battery systems under development for
residential
> applications that will operate at several hundred volts.  They will be
> using "sealed" VRLA batteries in sealed cabinets (factory service only).
>
> UL and NFPA have standards that indicate that an additional shock hazard
> potential exists at voltages above 50-60 volts.  In the 2002 Code
> submissions, the PV industry and Code Making Panel 3 are attempting to
> clarify that 50 volts refers to 24, 2V cells connected in series or a
> nominal 48V battery bank.  We are trying to allow the nominal 48V battery
> bank, but impose additional safety provisions on battery banks operating
> above a nominal 48V.  We need to be careful with the use of the terms
> "nominal" and "system" voltage because they are defined in different ways
> throughout 690 and the rest of the code.  We may or may not get all of the
> proposed changes accepted.  We will not know for a year or so as the
> process continues.
>
>
> In general, the term "accessible" in the Exception to 690-7(b)(1), would
> indicate that the exposed terminals of the batteries or battery cables
> operating above 48V nominal should not be accessible without using some
> sort of tool.  See definitions in Article 100.  A locked battery cabinet
> would also meet the requirement.  The same requirement applies to the
> common 120V ac outlet.  The intent is that the person who can use the tool
> to open the area where the batteries (and terminals) are located is
> qualified to be in that area.
>
> Of course, there are always the questions:  Is the conductive battery
> electrolyte "live"?  And is the conductive acid/dirt film on the tops of
> batteries "live"?  There have been shocks, fires, and explosions related
to
> this film on higher voltage battery banks (over 48V).
>
> Live parts would be considered guarded if they were in an area with
limited
> accessibility as discussed above.  There are also commercially available
> boots that fit over battery terminals that would also "guard" live parts.
> Surrett and other battery manufacturers and the motive power battery
> manufacturers use them and they are used in large UPS battery
> installations.  These, of course, can be easily removed by hand without a
> tool so they would not meet the requirements of Section 690-71 (b)(1) if
> the battery voltage were above 48V nominal.
>
> As the 1999 NEC stands in relation to 690-71, the installer has the
> following options with respect to code as I see it.  The local electrical
> inspector (authority having jurisdiction) may have other ideas and has the
> final say.
>
> All exposed current-carrying battery terminals should be guarded (covered)
> in battery systems for dwellings at any voltage.  If a tool is required to
> get to unguarded terminals such as a screwed shut battery box or a locked
> room, then the requirement appears to be met.  I like the large poly boxes
> sold by Walmart and Home Depot that will hold 4-6 L-16s and have lockable
> covers.  There are also battery boxes made by vendors in the PV industry.
> As far as I know, there are no listed battery enclosures (yet) that meet
> the NEC requirements for listing although there may be some listed to
> Telcom standards.
>
> If the installer is not overly concerned with the safety of the people in
> the vicinity of the batteries, then the code has no requirement that they
> be installed in any sort of box or enclosure if they are 48 volts nominal
> or below.  I, for one, would not make such an installation due to the
> additional hazard of acid around a battery bank.
>
> When installing an over-48V-nominal battery bank, the code appears to
> require that the battery bank be enclosed and access be limited since we
> have no readily-available way to keep little fingers away from the
> terminals.
>
> With shock hazards, short-circuit hazards (even on 6V batteries), and acid
> hazards, I always recommend installing batteries in non-conductive, acid
> proof enclosures with screwed down or locked covers.
>
> You are correct that there is no specific mention of wind-power systems in
> the code-yet.  However, as fixed electrical power systems, the NEC applies
> to wind-electrical systems as it does to all other similar fixed
electrical
> power systems.  The same electrical inspectors that inspect PV systems
also
> inspect wind systems and some of them seem to be applying similar
> requirements to all RE systems.
>
>
>
>
>
> 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)
> SWTDI/NMSU
> 1505 Payne Street-Campus
> Box 30001/MSC 3 SOLAR
> Las Cruces, NM 88003
>

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