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" <h...@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-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@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.brear...@solarprofessional.com
Direct: 541.261.6545
On 7/19/11 2:19 PM, "Hans Frederickson" <h...@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-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf
Of *Kent Osterberg
*Sent:* Monday, July 18, 2011 10:07 PM
*To:* g...@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
g...@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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