3.3 Flooring & Grounding Architecture

The floor is the primary electrical foundation of the EPA. It serves as the primarysole ground path for mobile personneloperators, carts, and carts.Autonomous ItGuided mustVehicles be(AGVs). conductiveIf enoughthe flooring system fails (becomes insulative), every step a technician takes generates triboelectric voltage that cannot drain to drainEarth. chargeWithout buta resistivefunctional enoughfloor-ground system, personnel are walking capacitors capable of carrying >3000V directly to protectthe personnel from electric shock.product.

The Resistance Requirements"Sweet (ANSI/ESD S20.20)Spot"

Flooring physics requires balancing two opposing risks: static dissipation vs. electrical safety.

Decision Logic: Resistance Zones

1. SystemIF Resistance (PersonR) +< Footwear1.0 +x Floor):10^5 Ω → THEN Must be < $3.5 \times 10^7$ ohmsFail ($35$ megohms) when measured per ANSI/ESD STM97.1.Conductive).
2. Walking Test (Body Voltage Generation): Peak voltage accumulation on a person walking must be < 100 Volts.

Grounding Hardware

• Common Point Ground (CPG): Every workstation must have a CPG block that connects the mat, the wrist strap, and the equipment chassis to Earth.
• Hard Ground vs. Soft Ground:
  • Equipment chassis:Risk: HardLethal Groundshock hazard. If an operator touches live voltage (110/220V), the floor provides a low-resistance path to ground, increasing current flow through the body.
• IF 1.0 Ohm)x 10^5 Ω ≤ R ≤ 1.0 x 10^9 Ω → THEN Pass (Dissipative).
• Personnel/Mats:Target: SoftThis Groundis (1the Megohmsafe resistoroperating inwindow. series)Charge drains within milliseconds, but resistance is high enough to limit current to safe levels (< 5mA).
• IF R > 1.0 x 10^9 Ω → THEN Fail (Insulative).
  • Risk: Charge accumulates faster than it decays. The floor is effectively an insulator.

Pro-Tip: Never wax an ESD floor with standard commercial polish. Standard wax is a dielectric insulator and will instantly destroy the floor's conductivity. Use only approved ESD-dissipative floor finish.

System Verification (The "Walking Test")

A conductive floor alone provides zero protection if the operator wears standard rubber-soled sneakers. We measure the System Resistance (Floor + Footwear + Person).

Performance Mandate

• Static Decay: The system must drain a 1000V charge to < 100V in caseless ofthan accidental2 seconds.
• Body Voltage Generation (BVG):
  • IF peak voltage on walking operator > 100 Volts → THEN Process Fail.
  • Action: Verify heel strap contact withor replace footwear.

Grounding Topology

The electrical connection to Earth (Earth Bonding Point) must be robust and distinct from the standard electrical neutral.

• Hard Ground (Chassis): Connect equipment chassis and machine frames directly to Earth (0 Ω impedance). This ensures breaker trips during short circuits.
• Soft Ground (Personnel): Connect wrist straps and table mats to Earth through a 1 Megohm (1 MΩ) current-limiting resistor.
  • Why: This resistor prevents the strap from becoming a lightning rod or a lethal path to ground if the operator touches a live voltage.wire.

Final Checklist

ComponentControl Parameter	ResistanceSpecification Range/ Limit	Test MethodFrequency	Owner
ESDSystem FloorResistance	$< 3.5 x 10^5$7 toΩ $10^9$(Person Ohms+ Floor)	SurfaceDaily Resistance Probe(Entry)	Operations
WorkstationsFloor Surface Resistance	< $1.0 \timesx 10^9$5 OhmsΩ – 1.0 x 10^9 Ω	Point-to-GroundQuarterly	Facilities
WalkingBody TestVoltage (Walking)	< 100 Volts Peak	ChargeSemi-Annual	ESD PlateLead
Ground MonitorImpedance	< 1.0 Ω (AC) to Equipment Ground	Annually	Facilities
Visual Inspection	No cracks, delamination, or wax	Monthly	Facilities