Conductive flooring is generally defined as a floor that reads below 1×106 ohms, and static dissipative flooring as one that reads from 1×106 ohms up to below 1×109 ohms, measured with weighted electrodes and a calibrated resistance meter. Those bands follow the common reading of the ANSI/ESD standards, but the written ESD control plan for your facility states the range that applies to your floor. If you are specifying conductive flooring and ESD epoxy in San Antonio, this guide covers the numbers an auditor checks, how the test is run, what moves a reading, and how often the test repeats.
Quick answer: the resistance bands that define conductive and dissipative
A floor is classified by how much electrical resistance it offers between a point on the surface and a groundable point. Conductive flooring sits at the low end, below 1×106 ohms. Static dissipative flooring sits in the middle band, from 1×106 ohms to below 1×109 ohms. A floor above that, and certainly one at or above 1×1011 ohms, is insulative and lets charge build up on shoes, carts and people.
Some specifications also set a lower limit on how low a floor may read, often in the region of 1×104 ohms, so that a person standing on the floor is protected if they contact mains voltage. Whether a lower limit applies depends on the governing document for the area, which is another reason to ask for the range in writing rather than relying on the word "conductive" on a brochure.
This guide stays strictly on measurement. If you want to know how an epoxy is made conductive, what additives are used and how the copper grounding grid is laid out, our guide to ESD epoxy additives and grounding covers that, and we will not repeat it here. If you are still choosing between a coating and sheet goods, see our comparison of ESD epoxy versus conductive vinyl. For the full overview of how an ESD epoxy floor works, start with the ESD anti-static epoxy flooring guide.
What ANSI/ESD S20.20 requires of a floor
ANSI/ESD S20.20 is a program standard, not a flooring specification: it requires a facility to build an ESD control program, and the floor is one of the elements that program can rely on. In practice the standard asks that people, footwear and flooring working together keep static charge below the level that could damage the sensitive parts the facility handles. The international counterpart is IEC 61340-5-1, which uses a similar approach.
For floors, the commonly cited requirements are of two kinds. The first is a resistance limit for the floor itself, measured to a groundable point, with a ceiling of 1×109 ohms. The second applies to the floor and footwear together: the combined system of person, footwear and floor is commonly held below 3.5×107 ohms, or alternatively the system is shown to generate less than about 100 volts on the body during walking. Which route a facility uses is part of its control plan, and which numbers apply to a given area comes from that plan, not from the flooring contractor.
That is why an auditor does not simply ask whether you have an ESD floor. They ask for the range your program set, the method used to measure it, the date of the last measurement and the readings themselves. Our guide to the compliance basics for electronics and defense facilities explains where the floor sits in a wider program.
Measuring to ANSI/ESD STM7.1: equipment, probes and procedure
Floor resistance is measured with a calibrated resistance meter and two weighted electrodes, following the test method in ANSI/ESD STM7.1 (the document that older specifications call S7.1). The test measures resistance in two ways: from a point on the surface to a groundable point, called resistance to ground, and between two points on the surface, called point-to-point resistance.
| Item | What the method calls for (typical) | Why it matters |
|---|---|---|
| Resistance meter | Calibrated, with a range that covers about 1×103 to 1×1012 ohms | An out-of-calibration meter invalidates every reading |
| Electrodes | Two weighted probes of about 5 lb (2.27 kg) each, with a conductive rubber contact face | Weight and face size set the contact area, so different probes give different numbers |
| Test voltage | Commonly 10 volts for lower readings and 100 volts for higher ones, as the method states | Voltage changes the reading on some materials |
| Electrode spacing | About 36 in (0.9 m) apart for point-to-point readings | Spacing is part of the definition of the number |
| Ground connection | A verified groundable point for resistance-to-ground readings | A reading to an unverified point proves nothing |
The exact weights, voltages and spacing come from the current edition of the test method and from the meter manufacturer's instructions, so treat the figures above as typical values to confirm against both. The procedure itself is straightforward:
- Prepare the surface. The floor is clean, dry and free of wax, dust and residue, because a film changes the reading.
- Record the conditions. Note temperature and relative humidity before the first reading.
- Place the electrodes. Set the probes flat on the surface, on the area being tested, away from seams, edges and fixed metal.
- Apply the test voltage and wait. Let the reading settle for the time the meter and method specify before writing it down.
- Repeat across a grid. Test enough locations to represent the whole floor, including the points farthest from the ground connection.
- Compare and record. Check every reading against the range your control plan sets and record pass or fail alongside the number.
The points farthest from the ground connection deserve extra attention. A floor can read well near a grounding point and fail across the room if the conductive path has been interrupted, for example by a topcoat applied too thick over a conductive layer. Point-by-point readings are what expose that.
Conductive against static dissipative against insulative, in numbers
Conductive and dissipative floors both control static, but they drain charge at different speeds. A conductive floor moves charge to ground quickly because its resistance is low. A static dissipative floor moves it more slowly, which is often what a facility wants around sensitive electronics, because a very rapid discharge through a component can itself cause damage. That is why dissipative flooring is the usual choice in electronics assembly, while conductive flooring is typically chosen where a fast discharge is a safety requirement, such as areas handling flammable or explosive materials.
An insulative floor does neither job. Standard epoxy, vinyl tile and floor wax all sit in this class, so a person walking across them can build up a charge that releases the moment they touch a sensitive part. The gap between the dissipative ceiling of 1×109 ohms and the insulative threshold near 1×1011 ohms is not a safe zone. A floor that reads in that gap does not meet either classification, so it is not accepted as an ESD floor under most specifications.
Resistance table: classification, range, typical application
| Classification | Resistance range (ohms) | Typical application | Note |
|---|---|---|---|
| Conductive | Below 1×106 | Areas with flammable or explosive materials, some laboratories and ordnance work | Fastest drain; some specifications add a lower limit near 1×104 |
| Static dissipative | 1×106 to below 1×109 | Electronics assembly, cleanrooms, defense and aerospace electronics, test areas | Controlled drain; common specification for electronics |
| Above the dissipative band | 1×109 to below 1×1011 | Not accepted as an ESD floor under most specifications | Reduces static but does not meet either class |
| Insulative | 1×1011 and above | Standard epoxy, vinyl tile, waxed floors | Charge builds and stays on the surface |
These bands are the common reading of the standards and of typical product data, not universal constants. A given system is formulated to hit a stated range, and the governing document for the facility decides which range is required. If the range printed in a quote does not match the one in your control plan, resolve that before the floor goes in, not after the first failed test.
How humidity, cleaning products and floor finish move a reading
A resistance reading is not a fixed property of the floor. It moves with conditions, and that is why test conditions are recorded next to every result. Readings taken in very dry or very humid conditions can differ enough to change whether a floor appears compliant, particularly for floors whose conductivity depends partly on surface moisture.
| Factor | What it does to a reading | What to do about it |
|---|---|---|
| Low humidity | Readings on many dissipative floors rise as the air dries | Record relative humidity and test at normal operating conditions |
| High humidity | Readings can fall, sometimes below the range that was intended | Compare readings only at similar conditions, or note the difference |
| Floor wax or standard finish | Adds an insulative film that raises resistance sharply | Never apply a general-purpose finish to an ESD floor |
| Cleaning product residue | Some leave a film that raises resistance; others are acceptable | Use only products approved for static control flooring |
| Wear, dirt and contamination | A surface layer of dust or oil changes the contact between probe and floor | Clean the test area the way the floor is normally cleaned |
| Topcoat thickness | Excess topcoat over a conductive layer can interrupt the conductive path | Check readings at points far from the ground connection |
Humidity deserves a note for San Antonio facilities. Summers are humid outdoors, but a conditioned electronics or defense facility is often kept much drier inside, and a floor accepted on a humid commissioning day can read differently in a dry winter. Record the relative humidity with every test and, if the readings will be compared year to year, compare them at similar conditions. If you are unsure which conditions your plan specifies, ask the engineer who owns the ESD control program rather than guessing.
As for floor finishes, a standard floor finish is insulative and will take a compliant floor out of specification. A well-meant waxing during routine maintenance is one of the most common ways a floor that passed at commissioning fails an audit a year later.
System resistance: the floor and footwear tested together
A floor does not protect anyone on its own. Static control works through the whole path from the person, through their footwear, through the floor and into ground, so the standard also looks at that path as a system. The person-footwear-flooring test is run with the person standing on the floor in the footwear they actually wear, holding a hand electrode, and the meter reads the resistance of the whole path to ground. Body voltage tests, in which the person walks and the charge on the body is measured, are the alternative route.
Two practical points follow. First, a floor that passes on its own can still fail as a system if the footwear is wrong, worn or contaminated, so footwear testing belongs in the same program. Second, a conductive floor paired with footwear that is not static control footwear can leave the system out of range. Ask which footwear your plan expects and test the combination that people really use, not a sample pair kept for audits.
Retest intervals and what to keep on file for an audit
An ESD floor is retested periodically through its service life, because cleaning products, floor finishes and wear all change surface resistance. The interval is set by the facility's ESD control program and is commonly annual, with higher-risk areas tested more often. It is also sensible to retest after any event that could change the surface: recoating, a repair, a new cleaning product or a change in maintenance method.
The test is only useful at audit time if the records are complete. A reading with no date, no conditions and no location is hard to defend. Keep a file that includes at least the following:
- Date and operator. Who tested, and when.
- Meter details. Model, serial number and the date of the last calibration certificate.
- Electrode details. Probe type and weight, so the test can be repeated the same way.
- Test voltage. The voltage used for each reading.
- Conditions. Temperature and relative humidity at the time of the test.
- A floor map. Test locations marked on a plan, so the next test uses the same points.
- Readings and results. The measured value at every point and a pass or fail against the control plan's range.
- Cleaning and finish history. The products used on the floor since the last test.
When ProEpoxy commissions an ESD floor, we provide a written test report with point-by-point resistance readings, so the first entry in that file is already in your hands on day one. If you are weighing contractors, ask each one for a sample report and check that it records the conditions, the meter and the locations, not just a pass. If you want a floor measured, specified or re-tested, call (830) 355-3303 for a free on-site measure and written quote, or read more about our ESD anti-static epoxy flooring in San Antonio.
Frequently asked questions
What resistance should an ESD floor have?
It depends on the classification being specified. Conductive floors occupy a lower resistance band than static dissipative ones, and the governing document for the facility states which range applies.
What is the difference between conductive and dissipative flooring?
Both control static, but conductive flooring moves charge to ground faster because its resistance is lower. Dissipative flooring bleeds charge more slowly, which is preferred where a rapid discharge would itself be a risk.
How often should an ESD floor be retested?
Periodically through its service life, because cleaning products, floor finishes and wear all change surface resistance. The facility's ESD control program sets the interval and the records support an audit.
Does humidity affect ESD floor readings?
Yes, which is why test conditions are recorded alongside results. Readings taken in very dry or very humid conditions can differ enough to change whether a floor appears compliant.
Can floor wax ruin an ESD floor?
Standard floor finishes are insulative and will take a compliant floor out of specification. Only cleaning products approved for static control flooring should be used.