[RE-wrenches] 1987 NEC

Tue Jul 19 13:29:26 PDT 2011

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 T
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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