becoming an inter-tie system [RE-wrenches]

[Bill Brooks]

William,

You are correct about the GFP (Ground-Fault Protector) being for fire
hazards. The original reason for including it in the code was for wood
construction with dc circuits in the attic. The requirement is limited to
dwellings. It is not at all for personnel protection. 0.5 amps through your
heart and you are dead. It is often misconstrued with its ac counterpart the
GFCI (Ground-Fault Circuit Interrupt), which is for personnel protection.

Many people dislike this requirement. I happen to think it does make sense
and protects against many other hazards related to ground-faults. If wires
are damaged during or after installation, or if modules are broken, it will
stop operation and indicate there is a problem. It also catches some wiring
mistakes. As PV arrays age, they can develop ground faults that need to be
fixed.

Bottom line is that it is a code requirement for rooftop systems on houses
(dwellings), and I will support its remaining in the code until I see a
really good reason to remove it. It is a fairly easy capability to add to a
batteryless inverter, and provides a reasonable value in safety for the
additional cost for battery-based systems.

Bill.

-----Original Message-----
From: William Miller [mailto:wrmiller at slonet.org]
Sent: Monday, February 19, 2001 10:08 PM
To: RE-wrenches at topica.com
Subject: Re: becoming an inter-tie system [RE-wrenches]


Pals:

Could the GFI be required to protect from fire hazard as well as, or
instead of, electrocution?  I try not to second guess Code requirements
unless I have some pretty substantial knowledge base, and I believe talking
a client out of a required device could be a liability nightmare.

William







At 10:32 AM 2/18/01 -0800, you wrote:
>Hiya Larry,
>Ah, the DC GFP! A device invented to fill a requirement written to
>correct a situation for which there was never a problem in the first
>place!
>Trace has the only one I know about. Roll your own can. I use them in
>48V systems every time (which ain't often because I try like hell to
>talk folks out of putting PVs on roofs, but sometimes you gotta) In
>24V systems I voice my opinions to the client and give them the
>choice knowing that they may have to pay me to install one later on
>IF the inspector requires it. What's the difference? Lifeform
>protection. There are no recorded instances of folks getting
>electrocuted by voltages less than 42VDC. Above that could, under the
>worst case scenario, potentially zap someone.
>Best, bob-O
>
>>Wrenches, I have a system on a customers house that consists of 4
>>SP75's roof mounted, a 4024 with a DC 250 disconnect, a C-40 charge
>>controller and 8 T-105's.  This is a grid connected house and we set
>>up a separate subpanel for the loads that run off the 4024.  The
>>grid feeds AC1 and acts as the back up.  Therer is no generator on
>>this system.  This system was always intended to grow as the
>>customers budget could afford.  Now we are adding 12 more SP75's on
>>the roof and they are going to inter-tie with the grid.  We will add
>>an outside disconnect to comply with requirements.  The question is
>>about GFI protection for the roof mounted array.  What has anyone
>>been doing to provide for GFI protection for roof mounted arrays?
>>and where in the control room equipment has anyone mounted the GFI
>>protection?  There is a 60 amp DC breaker mounted in the DC250 from
>>the array on the way to the C-40
>>Thanks for any feedback
>>
>>Larry Brown
>>Sun Mountain
>
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__________________________________________________________________
William Miller
SLO Communications: Communications and Power Systems Consulting
Chief Engineer, KCBX: NPR and PRI for San Luis Obispo and Santa Barbara
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email: wrmiller at slonet.org
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 michael.welch at homepower.com

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