Fw: Fw: Module grounding revisited [RE-wrenches]

[Allan Sindelar]

Here's John Wiles' response to William's question on rack versus module
grounding:
> Allan:
>
> No.  This comes up every year.  I address it at least once a year in
> Code Corner.  I wish more people would read it.
>
> Early in the days of PV (early to mid 1970's), Jet Propulsion Labs,
> Underwriters Laboratories (UL) and the PV module manufacturers
> determined through extensive and widespread testing and field
> experience that it was not possible to obtain adequate module
> grounding through the mounting bolts used to fasten the module frame
> to a grounded mounting structure.
>
> Aluminum oxidizes very easily and quickly.  The oxidation is an
> insulator.  Anodized modules (brown or other color) are also
> insulated by the anodizing.  These insulators are hard to break down
> and hard to stay broken down with normal mechanical fastenings of
> module frames to module racks.
>
> For this reason, UL Standard 1703 requires that a specific grounding
> point be identified and hardware be supplied for each module to
> ensure that the proper grounding is made and maintained.  This is
> usually a self tapping screw made of stainless steel that must cut
> 2.5 threads in the aluminum module frame.  Some modules have threaded
> stainless steel inserts to meet this requirement.  UL tests this
> grounding connection for continuity and voltage drop with current
> injection to all other parts of the module frame and to any other
> exposed metal on the module.
>
> The NEC requires that all equipment be installed in full compliance
> with any instructions or labels furnished with the product.  The
> module instructions and the marked green grounding point on the frame
> override any general requirements found in either Article 690 or in
> other sections of the code.
>
> >John, is William correct as you see it?
> >Allan
> >
> >----- Original Message -----
> >From: "William Miller" <wrmiller at slonet.org>
> >
> >Friends:
> >
> >I am researching some new module mounting for rooftops-- more on that
later
> >as it develops.  One question pertinent to the design is module frame
> >grounding.  One concept I had been wanting to research is that of
grounding
> >only the rack frame.  The Code seems to allow this:
> >
> >690.43 Equipment Grounding.
> >Exposed non-current-carrying metal parts of module frames, equipment,
> >and conductor enclosures shall be grounded in
> >accordance with 250.134 or 250.136(A) regardless of voltage.
> >
> >Researching further:
> >
> >250.136 Equipment Considered Effectively Grounded.
> >Under the conditions specified in 250.136(A) and (B), the
> >non-current-carrying
> >metal parts of the equipment shall be considered effectively grounded.
> >(A) Equipment Secured to Grounded Metal Supports. Electrical equipment
> >secured to and in electrical contact with a metal rack or structure
provided
> >for its support and grounded by one of the means indicated in 250.134.
> >The structural metal frame of a building shall not be used as the
required
> >equipment grounding conductor for ac equipment.
> >
> >Therefore, if one grounds a rack frame, the modules being "secured to and
> >in electrical contact with" the racks renders the module frames
> >"effectively grounded".
> >
> >Comments?
> >
> >William Miller
> >

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