ESD Chair Fails Resistance Test: Check Seat, Gas Lift, Base, Casters and Floor in Order

An ESD chair fails when the resistance from seat to ground is 1×10⁹ Ω or higher. The fault usually lies in a seat cover, a dirty PU seat, casters or glides replaced with ordinary ones, or a non-conductive floor. PRIMEAG recommends measuring segment by segment to know whether to replace casters, glides or the whole chair.

At the end-of-quarter audit in a factory in Vietnam, the QA team put red tags on a whole row of chairs on the assembly line. No need to buy a new batch yet: a rejected chair usually has only one broken link.

ESD chair fails the test: where the charge path runs

An ESD chair does not “absorb” charge; it provides a continuous path to ground: PU or ESD fabric seat → seat plate → gas lift → star base (aluminum, stainless steel or nylon) → conductive casters, conductive glides or drag chain → ESD floor → ground point. One insulating link breaks the whole chain.

Six things to check, in order

1. Anything covering the seat

Shipping plastic film not yet removed, chair covers, ordinary cushions brought in by operators. A common fault, fixable on the spot.

2. Dirty PU seat or cleaner residue

Hand oil, adhesive and dust build up into a film; some cleaners leave an insulating coating. Wipe clean, let dry and measure again.

3. Casters or glides replaced

Broken casters are often replaced with office-chair casters that look the same but do not conduct. Even the correct casters stop working when coated with adhesive or wrapped in thread.

4. Star base without a conductive path

A nylon base only conducts if it is made of conductive nylon or has a part connecting the gas lift to the casters; chairs assembled with mixed bases easily lose continuity here.

5. The floor underneath

Ceramic tiles, ordinary epoxy or a waxed ESD floor all block the path to ground. ESD PVC floor tiles 600×600 come in a conductive version of 10⁴–10⁶ Ω and a dissipative version of 10⁶–10⁹ Ω.

6. Measuring method

Measure to ANSI/ESD STM 12.1: a 5 lb electrode on the seat, with the chair standing on a grounded metal plate; measuring with the chair on the ESD floor tests the whole chair–floor system. Placing the electrode off-center on a plastic edge or measuring with the film still on gives wrong readings.

Isolating the fault with two split measurements

Use the TR1800 digital resistance meter with two 5 lb electrodes, measuring first seat → caster/glide, then caster/glide → floor.

Replace casters, glides or the whole chair?

Conductive casters and glides can be replaced separately. Replace the chair only when the PU seat is cracked or torn, or the seat → base segment is still high after cleaning and changing casters. PRIMEAG chairs carry a 12-month warranty. The ESD chair with backrest and ESD stool ranges offer cast aluminum, chrome-plated steel or conductive nylon bases, with conductive casters or glides.

Self-check after the fix

• Log each reading with temperature and humidity.

For areas with dozens of chairs bought from several sources, PRIMEAG can visit your factory (Dong Nai, Binh Duong or Ho Chi Minh City) to measure seat-to-ground resistance of the whole row free of charge, including chairs not bought from PRIMEAG, and send a PDF with the readings and a photo of each chair, so you can see which ones only need new casters or glides (free on-site ESD resistance testing); results are for reference only and are not audit documents.

Similar faults occur with ESD trolleys failing the test after a few months, ESD shoes failing after washing and ESD bench tops failing in some zones.

Frequently asked questions

• What resistance should an ESD chair measure? — Seat to ground must be below 1×10⁹ Ω; when buying new chairs, choose materials of 10⁶–10⁹ Ω to keep a safety margin.
• How often should ESD chairs be re-tested? — ANSI/ESD S20.20 does not set a fixed test interval; high-risk areas usually test monthly or quarterly.
• Can stainless steel chairs or saddle stools replace ESD chairs? — No. Stainless steel, FRP and saddle chairs are not designed or tested to STM 12.1. If you need ESD seating, choose an ESD chair with backrest or an ESD stool.