becoming an inter-tie system [RE-wrenches]

Tue Feb 20 10:19:00 PST 2001

<x-flowed>Hi Wrenches,

The new DC ground fault technology is certainly much better than the old 
Pulse systems.  But I still have a major problem with it.

If the device is to protect the wood framing between the solar modules and 
the charge control, it needs to be mounted on the roof.  If the wire were 
to become shorted (for example with a nail through a cable) the current 
would continue to circulate between the nail and the array.  Heating could 
result, especially with a large array.

A roof mounted ground fault device would likely pose more danger to home 
owners who might climb on the roof to correct nuisance tripping than it 
would eliminate danger from fire.  I suppose a device could be developed 
that would have a reset in the power room and ground fault protection by 
the array.

I believe that better protection could be afforded by using armored cable 
or conduit to protect the circuit.

Have there been any recorded fires from roof mounted arrays?  If there 
really are fire hazards from roof mounted arrays, they should be addressed 
effectively.  I am skeptical about the effectiveness of the current 
technology.

I also doubt that a roof mounted array is as dangerous as a 240 volt 
service drop coming from a pole, capable of delivering 10,000 amps.  There 
seems to be a tendency to require RE installations to be 10 times safer 
than grid connected systems.  Why is that?

Drake

At 10:40 PM 02/19/2001 -0800, you wrote:
>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
>PO Box 50, Santa Margarita, CA 93453
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 www.homepower.com

For info contact list moderator by email:
 michael.welch at homepower.com

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Newsletters, Tips and Discussions on Topics You Choose.
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</x-flowed>