Thanks, David. I've been looking for a 1987 NEC because of this
reference and others where John Wiles has referred to it.
David Brearley wrote:
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 ™
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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