Please refer to ANSI/EOS/ESD-S6.1-1991 "Grounding-Recommended Practice"
This standard is coordinated with the National Electrical Code and the IEEE
Green Book. Paragraph 4.12 states " In regard to a resistor between the
common point ground terminal and a worksurface, floor mat, or shelving:
-Where provisions are not made and not required for this resistor, a direct
connection is fully acceptable and recommended;
-provisions may be made to include a resistor where it may be required for a
purpose other than
ESD;
- conductive worksurfaces such as stainless steel shall be hard ground
connected.
Please note that ASTM D 257 is not suitable for use in measuring the
electrical resistivity/conductivity of moderately conductive materials. Use
test Method D 4496 to evaluate such materials.
For ESD purposes , it is recommended that resistance measurements of
worksurfaces be done in accordance with ESD S4.1-1997 ESD Association
Standard for the Protection of Electrostatic Discharge Susceptible Items-
Worksurfaces-Resistance Measurements.
All ESD standards and information are available from:
Electrostatic Discharge Association
7900 Turin Road, Bldg3, Ste 2
Rome,Ny 13440-2069
Phone: 315-339-6937c-----Original Message-----
From: Kane, Joseph [mailto:[log in to unmask]]
Sent: Wednesday, May 24, 2000 8:47 AM
To: [log in to unmask]
Subject: Re: [TN] Question on EIA-625 : Technical specs of Grounding
resis tor
Ashok:
Your static-protective bench mat probably came with a ground cord which
already incorporates a one megohm resistor. I haven't seen any that don't
ship that way, but if you don't have a protective ground cord, you need to
buy one or make one, for all of the good reasons already mentioned.
It's good practice to check mat resistance after installation and
periodically thereafter, because resistors go bad, mats get dirty and build
up insulating layers, and ground connections sometimes get kicked loose. We
use constant monitors for ground and check every 6 months using a 5 pound
weight, and accept if resistance from mat surface to ground is between about
10E5 to 10E9 ohms. For safety reasons, we have our operators disconnect
from ground before applying high voltages, as in hi-pot testing.
With flooring systems, it's a little more complicated.
JESD625-A (revision of EIA-625) is available at www.jedec.org.
Joe Kane
Lockheed Martin Control Systems
> ----------
> From: Mel Parrish[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Mel Parrish
> Sent: Tuesday, May 23, 2000 9:27 PM
> To: [log in to unmask]
> Subject: Re: [TN] Question on EIA-625 : Technical specs of Grounding
> resistor
>
> 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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