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Question What’s the ANSI/ESD S20.20 requirement for the ESD protected area grounding system?

Here’s some basic grounding information:

ANSI/ESD S20.20 Table 1 Grounding / Equipotential Bonding Requirements

Technical Requirement

Implementing Process

Test Method

Required Limit(s)

Grounding / Bonding System

Equipment Grounding Conductor


< 1.0 ohm impedance

Auxiliary Ground


< 25 ohms to Equipment Grounding Conductor

Equipotential Bonding


< 1.0 x 10E9 ohm1

1 The maximum resistance between any ESD technical element and the common connection point.


AC Equipment Ground “Within an EPA, the AC equipment ground is the preferred ground when available. The equipment grounding conductor electrically bonds the AC equipment ground to the ground bus at the main service equipment panel of the facility. AC equipment within the EPA and all of the ESD technical elements will be at or near the same electrical potential when this system is used.” [Grounding ANSI/ESD S6.1-2009 section 5.1.1]


Auxiliary Ground  “Some facilities require the use of a separate or supplemental ground system. When this is the case, the auxiliary ground shall be bonded to the AC equipment ground when possible. In the event that it is not possible to electrically bond the two ground systems, it should be noted that AC equipment and the ESD technical elements might be at significantly different electrical potentials.” [Grounding ANSI/ESD S6.1-2009 section 5.1.2]


“An auxiliary ground should be bonded to the equipment ground to ensure that there is no difference in electrical potential between the two systems.” [Grounding ANSI/ESD S6.1-2009 section 5.2.2 Auxiliary Ground System]


AC Equipment Ground and Auxiliary Ground Verification “If both grounding systems are present, the resistance between the AC and the auxiliary ground shall be <25 ohms.” [Grounding ANSI/ESD S6.1-2009 section 6.3.2 AC Equipment Ground and Auxiliary Ground Verification]

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