The only danger I see is injection of unwanted potential into the mat. A GFI
(Ground Fault Interrupt) on the equipment circuit would eliminate that
possibility and is a good practice anyway. "Common" ground in some old
factories may have significant voltage potential. The GFI will trip under
those conditions, drive maintenance crazy for a little while, but it will
prevent EOS damage caused by the conditions that your old policy attempts to
prevent.

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Jim Jenkins
> Sent: Thursday, May 30, 2002 2:26 PM
> To: [log in to unmask]
> Subject: [TN] ESD and equipment isolation
>
>
> Hi everybody,
>
> One of our internal specifications states that processing
> equipment needs to
> be "electrically isolated" from the static dissipative mat.  We are
> interpreting this to mean that if the equipment has a metal case it is not
> allowed to be in contact with the mat.  There has been some
> controversy over
> this, because we have whole areas and labs that have test equipment and
> other items that do not have the little feet on the bottom and
> make contact
> with the mat.
>
> We have people arguing on both sides here.  Some say that the contact
> provides a direct path to ground taking out the resistance needed to slow
> down the discharge.  I say that the dissipative (rather than conductive)
> nature of the mat provides the necessary resistance.  That is why
> resistors
> are no longer required in ESD specifications.
>
> Others say that the equipment can inject electrical energy through the mat
> into the ESDS devices.
>
> What do you all think?
>
> Thanks,
>
> Jim Jenkins
>
> [log in to unmask]
>
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