[RE-wrenches] 1987 NEC
boB Gudgel
boB at midnitesolar.com
Tue Jul 19 15:32:47 PDT 2011
On 7/19/2011 2:34 PM, David Brearley wrote:
> Presumably the latter---added as part of the cycle of revisions
> initiated in 1987.
The array shorting requirement must have gone away near 1993 or 1994 as
I designed an opening and shorting of the array style GFPD version in
1994 while at Trace Engineering.
It would have been expensive.
boB
>
>
> On 7/19/11 3:29 PM, "Hans Frederickson" <hans at fredelectric.com> wrote:
>
> David,
> Thanks for the interesting history on GFPDs. My copy of the 1987
> NEC does not have 690-5, and it's not missing any pages. Either my
> code book is an incomplete printing or perhaps John Wiles was
> referring to a 1987 proposal that didn't make it into the code
> until the 1990 NEC.
>
> Regards,
> -Hans
>
> ------------------------------------------------------------------------
> *From:* re-wrenches-bounces at lists.re-wrenches.org
> [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of
> *David Brearley
> *Sent:* Tuesday, July 19, 2011 12:57 PM
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] 1987 NEC
>
> Hans,
>
> John Wiles described the evolution of this standard for a Home
> Power article that we referenced later in a SolarPro on PV System
> Ground Faults:
>
> http://solarprofessional.com/article/?file=SP2_5_pg60_Mync
>
> "As described by John Wiles, program manager for the Institute for
> the Energy and the Environment, in the February/ March 2008 Home
> Power article "Ground-Fault Protection Is Expanding," Article
> 690.5 was added to the /NEC/ in 1987. One of Wiles' first projects
> in the PV industry was to develop "prototype hardware" to meet the
> new /Code/ requirement. "The basic concept (of the original GFPD
> prototype)," writes Wiles, "was to insert a 0.5- or 1-amp circuit
> breaker in the dc system-bonding conductor." This small circuit
> breaker senses any current between the grounded current-carrying
> conductor and the grounding system, tripping if current exceeds
> the 0.5 A or 1 A rating. By mechanically linking this smaller
> breaker to larger capacity breakers that are installed inline with
> the ungrounded current-carrying array conductors, it is possible
> to detect, interrupt and indicate that a ground fault has
> occurred, and to disconnect the fault.
>
> These early GFPDs were manufactured for 48 V or lower PV systems.
> According to Wiles, "As higher voltage, utility-interactive PV
> inverters became available in the late 1990s, using a 0.5- or
> 1-amp fuse as the sensing element and the inverter's control
> electronics to monitor the fuse was more cost effective." While
> the sensing equipment may have changed, in general the role of the
> modern GFPD remains the same as it was in 1987:
>
> 1. Detect ground faults in PV arrays.
> 2. Interrupt the fault current.
> 3. Indicate that a ground fault has occurred.
> 4. Disconnect the faulted part of the array.
>
> These four GFPD requirements for grounded PV arrays are spelled
> out in /NEC/ 690.5(A) and 690.5(B). The former requires
> ground-fault detection and interruption (GFDI), which includes the
> provision to indicate the presence of a ground fault. The latter
> requires that faulted circuits be isolated either by disconnecting
> the ungrounded conductors of the faulted circuit or by shutting
> down power to the output power circuits of the inverter or charge
> controller.
>
> A final GFPD requirement is found in Article 960.5(C), which calls
> for a visible warning in the proximity of the ground-fault
> indicator. The warning could be an LED, an LCD or both. In
> general, the manufacturer provides this electric shock hazard
> warning as part of the listed grid-tied inverter or charge
> controller. However, where a PV system includes batteries, the
> installer must apply a duplicate warning label near the batteries,
> stating:
>
> WARNING
> ELECTRIC SHOCK HAZARD
> IF A GROUND FAULT IS INDICATED, NORMALLY
> GROUNDED CONDUCTORS MAY BE UNGROUNDED
> AND ENERGIZED
>
>
> One change in the GFPD requirements introduced in 1987 is that it
> is no longer necessary to short-circuit, or "crowbar," the PV
> array in the event of a ground fault. This added step had the
> effect of reducing the PV array voltage to zero, minimizing shock
> hazard. The requirement was dropped in a subsequent /Code/ cycle,
> as leaving the array in a short-circuited condition created
> several other issues."
>
>
> If you're a Home Power subscriber, you can access the original
> article in the HP archives. If not, it is summarized above.
>
> Best,
>
> David Brearley, Senior Technical Editor
> /SolarPro/ magazine
> NABCEP Certified PV Installer ^(TM)
> david.brearley at solarprofessional.com
> Direct: 541.261.6545
>
>
> On 7/19/11 2:19 PM, "Hans Frederickson" <hans at fredelectric.com> wrote:
>
> Kent,
> I'm not a geezer yet, but thanks to my dad I do have a copy
> of the 1987 NEC. 690-5 (Ground Fault Detection and
> Interruption) was added in the 1990 NEC. There is no 690-5 or
> mention of ground fault detection/interruption in the 1987 NEC.
>
> In the 1990 NEC, section 690-5 is very small compared to 690.5
> in the 2011 NEC. Here's the complete text from 1990:
>
> "690-5. Ground Fault Detection and Interruption. Roof-mounted
> photovoltaic arrays located on dwellings shall be provided
> with ground-fault protection to reduce fire hazard. The
> ground-fault protection circuit shall be capable of detecting
> a ground fault, interrupting the fault path, and disabling
> the array."
>
> The handbook for 1990 goes on to say that the gfp device must:
> 1) detect the ground fault
> 2) open the grounded conductor to interrupt the ground fault
> 3) open the ungrounded conductors and short the photoltaic
> array source to disable it
>
> For some reason, I've never heard of item #3, specifically the
> part about shorting the array. Can anyone shed light on this?
>
> Regards,
> -Hans
>
>
> ------------------------------------------------------------------------
> *From:* re-wrenches-bounces at lists.re-wrenches.org
> [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On Behalf
> Of *Kent Osterberg
> *Sent:* Monday, July 18, 2011 10:07 PM
> *To:* gary at icarussolarservices.com; RE-wrenches
> *Subject:* Re: [RE-wrenches] 1987 NEC
>
> Gary,
>
> No one else has come up with a 1987 NEC. If you can get a
> copy of 1987 section 690.5 (I think it was 690-5 back then),
> I'd appreciate it.
>
> Kent Osterberg
> Blue Mountain Solar
>
>
>
> Gary Willett wrote:
>
> Kent:
>
> I am a member of the International Association of
> Electrical Inspectors (IAEI), and they're headquartered
> here in the Dallas area.
>
> If you aren't successful getting the info from a Wrench
> with the 1987 code book, let me know and I am sure I can
> request a FAXed copy of 1987 section 690.5.
>
>
>
>
>
> Regards,
>
> Gary Willett, PE
> Gary at IcarusSolarServices.com
>
> On 7/15/2011 4:30 PM, Kent Osterberg wrote:
>
> I'm looking for the text of 1987 NEC 690.5 to
> compare with 2011 version. If any of you geezers have
> kept copies that old, please contact me off list.
> Thanks.
>
> Kent Osterberg
> Blue Mountain Solar
> _______________________________________________
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