Interesting Mel. What is the process for calculating the grounding resistor, based on
equipment operating voltage?
Dave Fish
Mel Parrish wrote:
> Lee and Ashok,
> While it is sometimes common practice to earth ground an ESD safe bench,
> resistance is required to reduce hazardous shock exposure of operators
> should they come in contact with an available voltage source at the bench.
> Additionally, the resistance level is as specified considering the common
> potential resource of 115VAC (solderin irons, lights, etc) and should there
> be higher potentials available, the resistance value will need to be
> reassessed. Increase in available voltage potentials requires equivalent
> increase in resistance value to provide operator protection from a path to
> ground. A 1M ohm resistance is inadequate if there is a 300 V resource at
> the bench. While assessing the aspects of a correct ESD bench it is
> important to keep in mind the possibility of parallel ground paths which
> reduce the effective resistence. MIL-HDBK-263 contains detailed information
> concerning these topics.
> It is also important to provide a decay characteristic for applied voltage
> potentials to bleed off without creating as great a potential for damage to
> sensitive components that could be in the path of a potential surge in it's
> effort to seek ground potential.
> EIA 625 as an ESD standard applies well to component environments but other
> standards such as the previous MIL-STD-1686 (with support of MIL-HDBK-263)
> and ESDA S20.20 may provide additional information that is useful for
> product assembly operations. IPC-A-610C has updated ESD information as well
> as graphics for ESD bench attachment.
> As for the attachments the major requirement is that it be rugged enough to
> withstand production environments and be monitored or tested to prevent
> processing equipment in a potential ESD hazard environments. Again the Mil
> Specs recommend at least a half watt resistor and I would add a protective
> covering to support the lead attachments (shrink sleeving)as well. A plus
> would be sleeving that allows visual inspection.
> Contact me if I can be of any assistance.
> Mel Parrish
> 201 Cedar Road
> Mullica Hill, NJ 08062
> [log in to unmask]
> 856 223 5828
>
> ----- Original Message -----
> From: Lee Whiteman <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, May 23, 2000 5:36 PM
> Subject: Re: [TN] Question on EIA-625 : Technical specs of Grounding
> resistor
>
> > >From my experience, one does not require a grounding resistor on table
> mats
> > / floor mats. In fact, I've connected them directly into earth ground.
> >
> > According to EIA-625, Figure 1 (page 8), the resistors for the static
> > dissipative work surfaces (R2) and the ESD protective floor mats (R3) are
> > optional. If you are using R2 and R3, the values should be specified by
> the
> > ESD equipment manufacturer. I don't think there are any special
> requirements
> > (wattage, material of construction, etc.) for this resistor.
> >
> > Lee Whiteman
> > Senior Manufacturing Engineer
> > ACI / EMPF
> > Telephone: (610) 362-1200; Ext. 208
> > FAX: (610) 362-1290
> > E-Mail: [log in to unmask]
> >
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Ashok Dhawan
> > Sent: Tuesday, May 23, 2000 6:51 PM
> > To: [log in to unmask]
> > Subject: [TN] Question on EIA-625 : Technical specs of Grounding
> resistor
> >
> > << File: adhawan.vcf >> For grounding Table Mats/ Floor Mats and
> > workstations, does grounding
> > resistor need special
> > characteristics e.g. Wattage, material of
> > construction, etc.
> > We intend to use 1M Ohms resistor. EIA-625 does refer
> > to EOS/ESD-S6.1 standard (
> > paragraph 7) for grounding details, if anyone has
> > that details on that.
> >
> > Thanks in advance for advice.
> >
> > Ashok
> >
> > --
> >
> > Ashok Dhawan P.Eng
> > Engineering
> > C-Mac Electronic Systems Inc.
> > 1455 Mountain Avenue
> > Winnipeg, Manitoba R2X 2Y9
> > Canada
> > Phone: (204) 631-7208
> > Fax: (204) 631-7294
> > E-mail: [log in to unmask]
> > www.cmac.ca
> >
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