S20.20 - 8.2 Personnel Grounding

Technical Questions
#1

Dear Expert,

Per ANSI/ESD S20.20 section 8.2 Personnel Grounding.
All personnel shall be bonded or electrically connected to the selected grounding/equipotential bonding system when handling ESDS items. The personnel grounding method(s) shall be selected from Table 2.
When personnel are seated at ESD protective workstations, they shall be connected to the selected grounding/equipotential bonding system via a wrist strap system.
For standing operations, personnel shall be grounded via a wrist strap or by a footwear/flooring system meeting the requirements of Table 2.
When garments are used to achieve personnel grounding, it shall be documented in the ESD control program plan. It shall also meet the groundable static control garment system resistance requirements defined in Table 2 and the groundable static control garment in Table 3.

Could you please advise below.

  1. When working while sit on ESD chair, we need to wear wrist strap all of time.
    My understanding: That mean person grounded via wrist strap not ESD chair. Is it correct?

  2. While standing working, we need to select one choice for personnel ground, between wrist strap or ESD shoes. Is it correct?
    My understanding: When select ESD shoes choice, while working with ESDS items such as PCBA or IC and sometime moving PCBA between two processes by person, Is there the ESD risk .

  3. When use the groundable smock and while sitting working, Do we need to ground via wrist strap and garment groundable or can select one?

Thank you in advance.

#2

Hello Natthawee,

I will try to answer your questions,

For question 1, while sitting a wrist strap needs to be worn to ground a person.
For question 2, if you have an ESD control floor and the proper footwear, then while standing the footwear/flooring system or the wrist strap system can be used. If an ESD sensitive part is moved and the personal are grounded with a footwear/flooring system there is very little ESD risk.
For question 3, if the smock is a groundable garment system, then the system has a wrist strap type of connection built into the smock. If it is just a groundable garment, then a wrist strap is required while sitting down.

Please post any additional questions that you may have.

#3

I would add one factor for question 2.

Your risk for damage depends on the sensitivity of the part/item you are moving. If you are compliant to S20.20-2021 then your footwear/flooring system will create a save environment up to 100v. But if your component is sensitive to 25v, than your risk is high and you will need to do something more.