[RE-wrenches] Lightning protection system

Joel Davidson joel.davidson at sbcglobal.net
Tue Mar 10 20:16:00 PDT 2009 

A few years ago, Bill Brooks or another wrench specified 5 ohms or less when 
measured with a special meter but I can't recall the meter. No problem if 
the ground is saturated, but lightning in the southwest US often comes in 
the storm front before the soaking rain.

----- Original Message ----- 
From: "Darryl Thayer" <daryl_solar at yahoo.com>
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Sent: Tuesday, March 10, 2009 6:51 PM
Subject: Re: [RE-wrenches] Lightning protection system


>
> Thanks Joel
> the Lightning and Transients research Institute has been closed, I am 
> sorry to say.  The paper is valuable and reassuring, if the module frames 
> are properly grounded, they act as a shield and will protect the PV source 
> and output circuits if they are shielded via conduit or coaxial cable. 
> This also implies the grounding system should be of low resistance.
> DAryl
>
>
> --- On Tue, 3/10/09, Joel Davidson <joel.davidson at sbcglobal.net> wrote:
>
>> From: Joel Davidson <joel.davidson at sbcglobal.net>
>> Subject: Re: [RE-wrenches] Lightning protection system
>> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
>> Date: Tuesday, March 10, 2009, 8:14 PM
>> In 1983 Arco Solar and the Lightning & Transients
>> Research Institute,
>> St. Paul, MN, presented a paper at the Greece PV conference
>> titled
>> "Ability of Photovoltaic Modules to Withstand
>> Lightning Strikes."
>>
>> Summary: The ability of glass superstrate and metal/plastic
>> substrate
>> modules to withstand lightning strikes was examined. Each
>> of 3 different
>> types of modules were exposed to 4 nearby and 1 direct
>> strike of high
>> voltage long arc simulated lightning (400,000 volts, 10,000
>> amps), and
>> to 1 direct strike of high current, long duration lightning
>> (150,000 to
>> 175,000 amps, 50,000 volts). Visual and electrical
>> examination
>> demonstrated that the high voltage strikes produced no
>> electrical damage
>> to the glass superstrate modules and little to the plastic
>> substrate
>> module. The high current, long duration strike resulted in
>> varying
>> degrees of physical damage to all modules but little or no
>> loss in
>> electrical performance.
>>
>> Conclusions: The experimental data indicate that a glass
>> front module
>> with a rigid metal frame is able to withstand almost any
>> lightning
>> strike if the frame is grounded to the earth. The metal
>> frame acts as a
>> grounding rod attracting all the current to it. However, a
>> strike which
>> breaches the integrity of the encapsulation might, under
>> some
>> conditions, eventually destroy the module. Data from the
>> field appear to
>> concur with the experimental data presented in this paper
>> but also
>> indicate that while the modules survive a lightning storm,
>> additional
>> protection may be required for the cabling, power
>> conditioning
>> equipment, and control systems. A grounding rod will
>> protect the array
>> from direct strikes but further protection is required for
>> induced
>> voltages and side flashes they can create. Shielding (e.g.
>> coaxial
>> cables) will protect the wiring. The terminals of the
>> balance of system
>> components can be protected by the use of nonlinear circuit
>> elements
>> known as terminal protection devices. These devices may be
>> nonlinear
>> resistors or varistors, semiconductor junction devices and
>> dielectric
>> breakdown devices or sparkgaps. The degree of protection
>> needed for any
>> particular installation will be determined by factors such
>> as site
>> location, size of the array, safety considerations and
>> cost.
>>
>> Joel Davidson
>>
>>   ----- Original Message ----- 
>>   From: Matt Tritt
>>   To: daryl_solar at yahoo.com ; RE-wrenches
>>   Cc: trang donovan
>>   Sent: Monday, March 09, 2009 11:04 AM
>>   Subject: Re: [RE-wrenches] Lightning protection system
>>
>>
>>   Hi Darryl,
>>
>>   Just to see what your take would be, and other's -
>> what would the case be should the modules have
>> non-conducting frames (or even no frames)is the case with
>> some systems on the market?
>>
>>   Matt T
>>
>>   Darryl Thayer wrote:
>> Yes the electric power and atmospheric grounding systems
>> should be connected together to serve as a larger better
>> grounding system.  The Electrical code requires that at only
>> one point does the neutral (grounded) conductor of the
>> electrical power system get connected to the grounding
>> system, this is to prevent the grounding electrode system
>> from carrying electrical power system currents.  The
>> electrical power system is to be grounded to prevent the
>> electrical power system from differentiating its self via
>> the injection of energy from other electric power sources
>> including atmospheric electrical energy.
>>
>>
>> The lightening protection system is to create a path from
>> the atmospheric energy to the earth grounding system.
>> ((Wind rain, dust and friction cause the atmosphere to
>> become charged relative to the earth, conducting objects can
>> build a charge if not electrically connected to the earth,
>> these current flow all the time, although they are small
>> sometimes, and in the case of a lightening strike incredibly
>> large.  Even small currents can build large voltages and
>> fail electronic components.
>>
>> The frames of solar modules are electrical conduction
>> components not normally charged that can present a personal,
>> and physical damage potential (life-property) if they become
>> charged by the electrical power system and therefor the
>> underwriters require they be protected by grounding.  This
>> accidental energy need to be safely returned to the
>> electrical power system, and properly this is called bonding
>> back to the neutral conductor.  This grounding is described
>> by the NEC in 690 and 250 primarily.   The frames of the
>> modules can become charged by atmospheric energy energy,
>> this energy needs to be returned to the earth, via the
>> lightening protection system, ie grounding electrode system.
>>  The code says little about this, however, it is addressed
>> in 690 and 250.
>>
>> Sorry I said so much.
>> Darryl
>>
>>
>> --- On Fri, 3/6/09, Drake Chamberlin
>> <drake.chamberlin at redwoodalliance.org> wrote:
>>
>>   From: Drake Chamberlin
>> <drake.chamberlin at redwoodalliance.org>
>> Subject: Re: [RE-wrenches] Lightning protection system
>> To: "RE-wrenches"
>> <re-wrenches at lists.re-wrenches.org>
>> Date: Friday, March 6, 2009, 8:47 AM
>> I didn't get a reply to the question about connecting
>> the GEC to the
>> lightning protection system on the 8 story building.
>> Although this
>> may seem like an intrinsically dangerous idea, a lightning
>> protection
>> system is required to be bonded to the building grounding
>> electrode system.
>>
>> "250.106 Lightning Protection Systems.
>> The lightning protection system ground terminals shall be
>> bonded to
>> the building or structure grounding electrode system."
>>
>> It would therefore seem that the suplemental ground could
>> connect to
>> that system as well, and in fact use the existing
>> conductor.  Any
>> input would be welcome.
>>
>> Thanks,
>>
>> Drake
>>
>>
>>
>>
>> At 09:19 PM 3/4/2009, you wrote:
>>     Hello Wrenches,
>>
>> Can the supplemental grounding electrode conductor be
>>       connected to a
>>     lightning protection system?
>>
>> We have a case where it would be difficult to run a GEC
>>       down a multi
>>     story building, but have a convenient copper wire, from
>>       a lightning
>>     protection system, that runs to a rod.
>>
>> Thank you,
>>
>> Drake Chamberlin
>> Athens Electric
>> OH License 44810
>> CO License 3773
>> 740-448-7328
>> 740-856-9648
>>
>>
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>>       Drake Chamberlin
>> Athens Electric
>> OH License 44810
>> CO License 3773
>> 740-448-7328
>> 740-856-9648
>>
>>
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