A change in floor resistance may reflect the flooring, the measurement equipment or the conditions during testing. A different reading does not, by itself, establish that the floor has deteriorated or that the original test was incorrect. Follow the specified test method and the instructions for the equipment being used.
Craftsman Concrete investigates ESD floor resistance results by checking the measurement equipment, test procedure and recorded site conditions. We test floors installed by Craftsman and other contractors and provide the facility’s ESD program team with findings and guidance on whether further testing or corrective action may be needed.
Confirm the meter can perform the required measurements
ANSI/ESD S20.20-2021 requires equipment capable of making the measurements defined in the facility’s compliance verification plan. A calibration certificate alone does not establish that capability.
Check the required resistance range, test voltages and equipment configuration. TR53-01-22 recommends apparatus capable of measuring at least one order of magnitude below the lowest required value and one order above the highest required value (section 6.13).
The resistance-meter requirements explain how equipment capabilities relate to the specified measurements.
Check power, leads and grounding
Power source
STM7.1-2020 warns that AC-powered resistance meters may produce erroneous results through undefined ground paths. It recommends battery-powered equipment.
The guide to battery-powered resistance meters explains that recommendation.
ASTM F150-25 separately recommends current-limited power supplies, usually below 5.0 milliamperes, for safety.
Test leads and reference connection
Examine leads for loose connections, breaks or disconnection. STM7.1 also identifies potential errors when unshielded or inadequately isolated leads contact the flooring. ASTM F150 states that test leads should be isolated from ground.
For a measurement to ground, confirm that the connection uses the reference required by the method. The grounding-reference guide distinguishes the applicable configurations and checks.
Inspect electrode contact surfaces
Contamination and contact condition can affect measurements. Follow the applicable method and manufacturer’s instructions for cleaning, then allow adequate drying before testing.
The STM7.1-2020 installed-floor procedure specifies an isopropanol-water solution and a clean, low-linting cloth, followed by air drying (section 6.2.1.1). TR53-01-22 directs users to remove electrode contamination according to the manufacturer’s recommendations (section 7.2.3.3).
The floor-test electrode guide covers electrode requirements and contact-related influences.
Warped conductive rubber contacts
STM97.1-2025 identifies that conductive rubber contacts can warp over time and change measurements, but provides no standardized method for verifying whether that has occurred (section 5.3 note).
Consider electrode condition alongside the flooring and other test conditions. The historical studies of floor-resistance measurement provide further context on how electrode contact can influence results.
Verify test voltage and reading time
Some flooring materials produce different resistance readings at different applied voltages. Follow the specified method’s voltage-selection and reading-time rules before comparing results.
For STM7.1-2020 installed-floor testing, measurements start at 10 volts and switch to 100 volts when the initial resistance is at or above 1.0 × 10^6 ohms. If the subsequent reading falls below that threshold, the procedure uses the 100-volt reading.
The STM7.1 test-voltage and reading-time guide gives the full sequence.
STM7.1’s informative Annex C describes voltage-induced breakdown as a possible material-dependent explanation for a lower resistance at higher voltage. It does not establish that breakdown causes every lower reading at 100 volts.
Check the instrument’s operating mode
The Prostat PRS-801B/PRS-812B Resistance System User Manual, covering those Prostat resistance meters, describes automatic voltage selection according to the measured resistance range.
On the PRS-801B, manual voltage selection is available only in MANUAL mode. AUTO, CONTINUOUS and AUTO-MANUAL modes select voltage automatically.
These instructions are specific to the named instruments. Confirm the operating mode and voltage behavior of the meter actually being used.
Verify the complete measurement setup
TR53-01-22 checks measurement capability in two stages after lead and electrode-condition checks:
- Verify that the meter and appropriate leads can measure above and below the expected resistance range.
- Verify the electrodes using that meter and the appropriate leads across the expected range.
The measurement-setup verification guide explains these checks.
Review humidity and instrument exposure
Ambient conditions affecting the floor
ASTM F150-25 notes that readings at lower relative humidity can differ from readings at higher humidity. TRGS 727 observes that surface resistance generally increases considerably as air humidity falls.
Document humidity alongside the readings so results obtained under different conditions can be compared appropriately.
Conditions affecting the instrument
The Prostat PRS-801B/PRS-812B manual warns that water, oil, solvents, conductive contamination and damp conditions can damage the instrument, affect measurements and create shock or arc-discharge hazards.
These equipment-specific warnings are separate from the effect of ambient humidity on the flooring’s resistance.
Frequently asked questions
Yes. Craftsman Concrete measures floor resistance and reviews the equipment, procedures and documented test conditions for floors installed by Craftsman or other contractors. The findings help the facility’s ESD program team determine whether equipment checks, further testing or corrective action may be needed.
Check the leads and grounding reference, electrode condition, equipment capability, test voltage, reading time and ambient conditions. Compare those details with the specified test method and previous records before deciding whether the difference reflects a flooring problem.
No. On the PRS-801B, manual voltage selection is available only in MANUAL mode. AUTO, CONTINUOUS and AUTO-MANUAL modes select voltage according to the measured resistance range.
Yes. ASTM F150-25 notes that readings can differ with ambient relative humidity, and TRGS 727 observes that surface resistance generally increases considerably as humidity falls. A difference between readings taken under different humidity conditions does not, by itself, establish flooring deterioration.