The EIA standard EIA-625, in section 6.3 and table 1, personnel grounding, states that:

The electrical path using a wrist strap (wrist band), ESD smock, and ground cord meets these requirements. The wrist strap must be worn snuggly to the wrist, making a good electrical contact with the wrist. The wrist strap is then snapped to the snap socket provided on the cuff of the garment (ESD smock). The smock provides a continuous electrical path to the hip snap socket. A wrist-strap coil cord is then attached to the hip snap socket extending the continuous electrical path through the coil cord to an ESD ground. The operator (human body) is then grounded via a wrist band with a continuous electrical path to ground using the smock material in series with the coil cord to ground.

The ground cord has an integral current limiting one megohm resistor molded into the snap socket at the end closest to the wrist band for personnel safety. The max voltage rating to maintain a current limit of less than 0.5 mA for our wrist strap coil cords (ground cords) is 250 VAC.

The ESD Association standard EOS/ESD S1.0 covers the use of personnel grounding wrist straps for protection of ESDS items. Under appendix A, A.3 grounding considerations, section A.3.1 states that antistatic or static-dissipative work surfaces should never be placed in series with wrist straps.

The factors of concern for the proper grounding of personnel for ESD purposes are:

1. Establishing a continuous path to ground from an electrically sound contact on the human skin.
2. The ground path allows for discharge times of less than 10 milliseconds.

An operator’s body movement is typically much greater than 50 milliseconds when performing normal work routines, i.e., picking up an object, moving an object, reaching, grabbing, etc. If the total ESD ground system removes all charge in well under 50 milliseconds, than the risk of an ESD event caused by an operator is squelched.

ESD Systems Smocks are woven with conductive carbon suffused nylon mono-filaments with a resistance of 10⁴ Ohms. The surface resistivity of the smock material is 1x10⁵ Ohms/ , at the borderline for classification as conductive. The sleeve to sleeve resistance is 4.5 x 10⁵ Ohms, is in the static dissipative classification. Plastic Systems smocks have discharge times of less than 10 milliseconds as published in the tech brief PS-2048.

The use of a functional wrist strap, ESD smock with conductive filaments, and a ground cord all connected in series to an ESD ground will provide adequate protection against possible operator induced ESD events.