Questions And Answers

ANSI/ESD S20.20 does not address this question.

Worksurface standard ANSI/ESD S4.1 does recommends a lower resistance of 1 x 10E6 ohms. Per ESD S4.1 section 8. Resistance Guidelines “Resistance-to-groundable point 1 x 10^6 to 1 x 10^9 ohms. Resistance from point-to-point greater than 1 megohm. These guidelines represent a range of resistance that has generally been proven to provide protection in the manufacturing environment.”

The worksurface material itself should have a resistance point to point (RTT) of 1 x 10E6 ohms to < 1 x 10E9 ohms. It would be quite a Charged Device Model (CMG) risk to achieve the 10E6 ohm resistance to ground (RTG) having a very conductive metal worksurface with a 1 megohm resister in the ground cord.

The Grounding standard ANSI/ESD S6.1 does recommend hard ground, but a 1 megohm resister is OK in the ground cord.

“The grounding conductors (wires) from wrist straps, worksurfaces, 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 point ground or common connection point is acceptable and recommended.

Note: Manufacturers may add resistance to the grounding conductors for purposes other than ESD (e.g. current limiting). Added resistance is acceptable for the purposes of controlling ESD provided electrostatic accumulation does not exceed specific EPA requirements. The typical added resistance in grounding conductors is 1 megohm, although other values may be specified.” [Grounding ANSI ESD S6.1 section 5.3.3 ESD Technical Element Conductors]

Our black ground cords contain a resistor while our green/yellow ground cords do not contain a current limiting resistor.