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Ground Trolleys in Series With Cords Having 1 Megohm Resistor

I am confused on ESD connections. I understand that you cannot clip a cord from a wrist strap to the edge of an ESD protective mat. I know that the cord for wrist straps has 1 megohm of resistance and that the point to connect the wrist strap cord should have less than 1 ohm to ground.

I have people using 2 meter high metal rolling trolleys. I believe the preferred method is to connect each trolley directly to a common ground point. Can several trolleys, say 3 to 5 be connected in series with 1 megohm cords with the final cord connected to a ground point or earth bonding point? From what I have read this would only mean about 5 megohms to ground at the furthest cart. I read somewhere something about staying under 35 megohms to ground. Now I cannot find that.

The compliance verification limit per EN 61340-5-1 for wrist strap system is less than 3,5 x 10^7 ohms listed in Personnel grounding requirements Table 2. The required limit per ANSI/ESD S20.20 for both working surfaces and mobile equipment (trolleys) is less than 1 x 10^9 ohms resistance to ground listed in EPA requirements Table 3.

It does not do much good to have an operator test their wrist strap using an integrated wrist strap tester as describe in IEC 61340-5-1 Clause A.1, but then work where the matting resistance is added resistance in the path-to-ground.

Although not recommended you could attach the cord for the wrist band to the matting material, and daisy chain the mats and/or trolleys if you could demonstrate that you reliably meet the required limits.

Per CLC/TR 61340-5-2:2008 User guide Wrist Strap subclause “NOTE Many wrist strap users have been observed to clip the wrist cord to the edge of an ESD protective mat. This process is not recommended as it can increase the total system resistance to ground to over the 3.5 x 10^7 ohms limit required by IEC 61340-5-1.”

Regarding daisy-chaining “All working surfaces need to be capable of being grounded. EPA grounding of instruments or surfaces by chaining, or by placing items in series should not be used, since in the event of a broken connection the risk of floating items and ESD damage will be unnecessarily increased.” [EN 61340-5-2 clause 5.2.2 Working surfaces and storage racks] Note that both of these recommendations are not requirements.

Regarding ground cords, the grounding conductors (wires) from wrist straps, working surfaces, flooring or floor mats, tools, fixtures, storage units, carts, chairs, garments and other ESD technical elements may or may not contain added resistance. Where added resistance is not present, a direct connection from the ESD technical element to the common ground point or common connection point is acceptable and recommended.

However, “A nominal 1 megohm resistor is commonly used in wrist straps and to ground work surfaces. In the event of an operator touching an energized conductor, for the normal mains electricity supplies this resistor will limit the current flowing through the person to less than 0,5 mA.” [User Guide IEC 61340-5-2-1999 subclause 5.1.1]

Charleswater sells ground cords with and without current limiting resistors – Click Here


Introducing New Statguard® Conductive Epoxy and Primer

71010 Statguard® Conductive Epoxy

  • Epoxide Polymer with Surface Resistance
    of RTT 10E4 – 10E6 ohms

    Coat concrete, wood, steel, and other surfaces to create a consistent path to ground for operators wearing a foot ground system.
  • One Coat, 2-part, Water-based Epoxy System
    Mix 4 gallon pre-measured part A and B
    together and install with squeegee and nap roller.
  • 50% Solids by Volume
    Easy to install and reduces dry time.
  • Made in United States of America

71011 Statguard® Epoxy Primer

  • Epoxy primer designed for use under
    71010 Statguard® Conductive Epoxy
    Use over concrete or other porous surfaces
    to increase spread and adhesion rate.
  • Made in United States of America
Item Description List Price
71010 Statguard®, Conductive Coating Epoxy, Light Grey, 15 L Kit $1673.99
71011 Statguard®, Epoxy Primer, 15 L Kit $781.30
“Permanent materials are broadly defined as floor coverings, including rubber or vinyl tile and sheet goods, epoxy coatings, high-pressure laminates, and carpet. As a group, these materials have an extended use life and provide protection over a broad physical area. [CLC/TR 61340-5-2:2008 User guide section Permanent floor materials]” Paints and epoxy coatings are applied to concrete floors in thin coats. The primary advantages of these materials are their ease of application and coverage over a wide area. They have a longer usable life than do floor finishes …” [CLC/TR 61340-5-2:2008 User guide section Paints and coatings]
Sign Up HERE | Request a Sample HERE | See list of sales reps and distributors HERE
All Items & programs are available through your participating distributor | Submit your questions HERE

Introducing Jewel® Workstation Mini Monitor

  • NEW Improved Banana Jack
    Creates a more consistent connection and helps to prevent accidental disconnects with operator’s wrist strap banana plug.
  • Replaces Item 99130
  • Can be used with any brand of single-wire wrist strap and cord
  • Single station Continuous Monitor for operator and ESD worksurface
  • Made in the United States of America
Item Description Price
99135 Jewel® Workstation Mini Monitor, 220VAC $132.09
Sign up HERE | Request a demo HERE | See list of sales reps and distributors HERE
All items & programmes are available through your participating distributor | Submit your questions HERE