Questions And Answers

I know that a one megohm resistor is required in the wrist strap cord which goes to the common point ground. Should the ground cord going from the common point ground also have a one megohm resistor?

If it is resistance in series, the path to ground would be 2 megohms (or 2 x 10E6 ohms) if in both wrist strap cord and ground cord.

Wrist straps cords are to have 0.8 to 1.2 10E6 ohms per ANSI/ESD S20.20-2007 Personnel Grounding Table 2 while the recommendation for ground cords per Grounding standard ANSI/ESD S6.1is hard ground.

Many customers do prefer a 1 megohm resistor in ground cords, and it does no ESD control harm. Note the paths of the banana jacks bypass the resistor so no added resistor is added for an operator wrist strap cord.

The wrist strap standard is ANSI/ESD S1.1 and the Grounding standard id ANSI/ESD S6.1.  Here’s the pertinent information from these documents:

“1. Current-Limiting Resistance, A resistance of sufficient resistance to limit current to less than 0.0005 amps (0.5 mA), at the highest voltage that may be encountered, should be incorporated into the wrist strap.  Nominally, 800,000 ohms (800 kilohms) are sufficient for voltages of up to 240 volts alternating current (AC). The value of 1 megohm is specified because it is a standard value discrete resistor.

Special situations may dictate the use of values above or below the 1 megohm value. Wrist straps with nominal resistances other than 1 megohm should be marked in accordance with paragraph 5.9.

Discrete current-limiting resistors should be located near the connection between the ground cord and the cuff.” [ANSI/ESD S1.1 ANNEX B]

“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 S6.1-2009 section 5.3.3 ESD Technical Element Conductors]

“The resistance of the conductor from the groundable point ground of any ESD technical element (e.g. worksurface, floor, chair, wrist strap, etc.) to the common point ground or common connection point shall not be greater than 1 ohm. Where a resistor is used in the grounding conductor, the total resistance shall include the value of the resistor.” [Grounding ANSI/ESD S6.1-2009 section 6.4.1]