A floor resistance-to-ground measurement includes the electrical path between the floor electrode and the grounding reference connected to the meter. That reference must be identified and verified before the result can be used to evaluate the flooring.
Craftsman Concrete performs floor resistance testing for systems installed by Craftsman and other contractors. Reviewing the grounding reference and its verification records helps the facility’s ESD program team determine whether further investigation is needed before interpreting the floor measurements.
ANSI/ESD STM7.1-2020 describes test-lead connections for installed-floor acceptance testing, while ESD TR53-01-22 addresses routine compliance verification. TR53 also provides procedures for verifying grounding references, and ANSI/ESD S20.20-2021 specifies grounding and bonding limits for programs governed by that standard.
Where the meter’s ground lead connects
Installed-floor acceptance testing under STM7.1
ANSI/ESD STM7.1-2020 connects one meter lead to ground, as defined in ANSI/ESD S6.1, and the other lead to the resistance measurement electrode.
This is part of the resistance-to-ground procedure for acceptance testing of an installed or applied flooring system (section 6.2.1.4).
Routine flooring verification under TR53
ESD TR53-01-22 connects the test leads as follows:
- The negative terminal of the resistance measurement apparatus connects to a previously verified ESD grounding/bonding reference point.
- The positive terminal connects to the resistance measurement electrode placed on the flooring being verified.
These connections appear in the flooring system resistance procedure (section 7.2.3.2.1, steps a–c).
What can serve as the reference point?
The TR53 grounding/bonding reference may be based on an equipment grounding conductor or an auxiliary ground. Each must be verified before use as the reference.
TR53 also permits a previously verified Level 2 technical element to serve as the reference point. A Level 2 technical element is connected in series to a common point ground or common connection point through another ESD technical element.
Verifying the grounding reference
Applicable jurisdiction and qualified personnel
The grounding verification procedures in TR53-01-22 derive from ANSI/ESD S6.1 and ANSI/NFPA 70. They are based on United States standards and should be modified or adapted for use outside the United States (section 7.1).
TR53 also notes that many countries require verification of grounding/bonding systems involving mains wiring to be performed by qualified personnel. Failures involving an equipment grounding conductor or auxiliary ground should be reviewed by qualified personnel.
Equipment grounding conductor: check receptacle wiring
TR53-01-22 uses a circuit tester to check the wiring orientation of the receptacle containing the proposed equipment grounding conductor (section 7.1.1.1):
- Connect the circuit tester to the receptacle.
- Verify that the hot and equipment grounding conductor wires are not reversed.
- Verify that the hot and neutral wires are not reversed.
Upon successful verification, the equipment grounding conductor can be used as the reference point under this procedure.
The circuit tester has limitations. TR53 notes that some testers cannot distinguish ground and neutral wire reversals or determine the equipment grounding conductor’s impedance to ground. A successful wiring check therefore does not necessarily establish compliance with a separate impedance limit.
Auxiliary ground: check resistance to the verified equipment ground
TR53-01-22 checks an auxiliary ground against an equipment grounding conductor that has already been verified (section 7.1.2.1):
- Set a DC ohmmeter to measure resistance in ohms.
- Connect the negative terminal to the previously verified equipment grounding conductor.
- Connect the positive terminal to the auxiliary ground being verified.
- Verify that the resistance between them meets the applicable requirements.
Grounding limits under ANSI/ESD S20.20-2021
Equipment grounding conductor and auxiliary ground
For an ESD control program governed by ANSI/ESD S20.20-2021, Table 1 specifies the following limits for the selected grounding/bonding process:
| Grounding/bonding process | Test method | Required limit |
|---|---|---|
| Equipment grounding conductor | ANSI/ESD S6.1 | Less than 1.0 ohm impedance |
| Auxiliary ground | ANSI/ESD S6.1 | Less than 25 ohms to the equipment grounding conductor |
These are grounding/bonding requirements. They are not the resistance acceptance limits for the flooring itself.
Facilities with a GFCI
Where a ground-fault circuit interrupter (GFCI) is installed, S20.20-2021 does not require the equipment grounding conductor measurement identified in Table 1. The associated footnote warns that the measurement may activate the GFCI (Table 1, footnote 4).
This exception concerns that specific measurement. It should not be treated as a general exemption from grounding verification.
Frequently Asked Questions
Yes. Craftsman Concrete reviews the grounding reference and available verification records as part of floor resistance testing for systems installed by Craftsman or other contractors. This helps the facility’s ESD program team identify whether further verification or investigation is needed. Electrical grounding failures should be reviewed by qualified personnel.
Not necessarily. TR53-01-22 notes that some circuit testers cannot determine the equipment grounding conductor’s impedance to ground or distinguish ground and neutral wire reversals. A wiring-orientation check and an impedance measurement answer different questions.
No. The limits in ANSI/ESD S20.20-2021 Table 1 apply to the grounding/bonding process: less than 1.0 ohm impedance for the equipment grounding conductor and less than 25 ohms from an auxiliary ground to the equipment grounding conductor. They are not flooring resistance acceptance limits.
No. ANSI/ESD S20.20-2021 exempts the equipment grounding conductor measurement identified in Table 1 where a GFCI is installed. Its footnote warns that the measurement may activate the GFCI (Table 1, footnote 4). The exception does not remove other applicable grounding requirements.