[RE-wrenches] 1987 NEC

Tue Jul 19 12:57:19 PDT 2011

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

³As 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 Wiles¹ first projects in the PV industry was to
develop ³prototype hardware² 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, ³As 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 inverter¹s control electronics to monitor the fuse was more
cost effective.² 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 ³crowbar,² 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.²

If you¹re 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.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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