4.2 Safety Testing

Safety testing is the checkpoint where electrical products earn the right to be trusted in human hands. It ensures that hazardous voltages remain isolated, protective earth paths are solid, and insulation can withstand real-world stresses without failing. Through a sequence of earth-bond checks, insulation resistance, and Hipot testing, hidden weaknesses such as poor connections, moisture, or design oversights are revealed before they can cause shocks, fire, or certification delays. Guarded stations and strict recipes make the process controlled, while traceable records transform safety from an assumption into hard proof.

4.2.1 Purpose (in one line)

Prove that hazardous voltage stays boxed-in and that accessible metal is either solidly earthed (Class I) or properly insulated (Class II)—with guarded fixtures and rules, not vibes.

4.2.2 What you actually test (fast map)

Protective Earth (PE) / Earth Bond — low resistance from PE pin to all accessible metal.
Insulation Resistance (IR) — gentle DC check that insulation is healthy.
Dielectric Withstand (Hipot) — short, high-voltage stress between hazardous and accessible circuits.
(If your spec calls it) Leakage Current — with mains applied, measure touch/earth leakage.

Sequence: Earth Bond → IR → Hipot → (Leakage). Stop on any fail; discharge before opening.

4.2.3 Class I vs Class II (choose the right playbook)

Device class	What that means	Must-run tests
Class I (earthed)	Accessible metal tied to PE (green/yellow)	Earth Bond, IR, Hipot (Primary↔Earth/SELV), (Leakage if spec’d)
Class II (double insulated)	No PE; reinforced insulation	IR, Hipot (Primary↔Accessible/SELV), (Leakage if spec’d)

Your product standard sets voltages/limits. The values below are starter ranges—always use the recipe from PE/QE.

4.2.4 Station safety (non-negotiables)

Interlocked enclosure; door locks during HV; E-stop reachable.
Bleed-down to < 30 V before door unlocks; visible “SAFE” lamp.
Guarded HV leads; no alligator clips on painted metal.
One-hand rule; ESD strap OFF during HV tests.
Daily self-test: verify outputs, trip, discharge. Log it.

4.2.5 Earth Bond (PE continuity)

What: Drive a high current through the PE path and measure resistance/voltage drop.

Setup

Bond point: PE pin → each accessible metal (trays, lids, heatsinks).
Test current: 10–25 A for 1–2 s (per spec); 4-wire preferred.
Scrape pads/serrated washers in place (23.1/23.2).

Starter limit: R ≤ 0.10 Ω (include test lead compensation).

Fail fast cues: loose lugs, paint under washers, long star-to-star stackups.

4.2.6 Insulation Resistance (IR)

Why before Hipot: it finds contamination/moisture without heavy stress.

Pairs to test (typical)

Primary (L+N shorted) ↔ PE/chassis (Class I).
Primary (L+N) ↔ accessible metal/SELV (Class I & II).

Starter setup: 500 VDC, 30–60 s dwell.

Starter limits: ≥ 100 MΩ benign devices; ≥ 10–100 MΩ rugged/EMI-heavy (agree with QE).

Dry to room conditions if humidity just came off a wash/soak.

4.2.7 Hipot (dielectric withstand)

What: apply HV for a short time and ensure no breakdown.

DC vs AC

DC Hipot: tolerant of EMI capacitors, clean leakage reading.
AC Hipot: stresses both polarities, sometimes required by spec.

Typical pairs & ranges (use your recipe)

Primary (L+N tied) ↔ PE/chassis: 1000–2000 VAC or 1200–2800 VDC.
Primary ↔ SELV/accessible circuits: same order of magnitude; higher for Class II.
SELV ↔ chassis: sometimes required (lower voltages).

Control the stress

Ramp 1–2 s → Dwell 2–3 s (longer for bulky filters) → Discharge to <30 V.
Trip/leakage windows set per product (mA scale for AC; mA/µA for DC).
If EMI Y-caps/MOVs cause nuisance trips: switch to DC, add ramp, or use the product’s test bypass (if designed). Never snip parts.

4.2.8 Leakage current

(when your standard calls for it)

With mains applied, measure earth/touch leakage in normal and single-fault (e.g., reversed polarity).

Use a compliant leakage tester and the network your spec defines.
Log mA RMS and test condition. Limits are standard-specific—the recipe must encode them.

4.2.9 Special parts to respect

MOVs/Surge suppressors line↔earth: AC Hipot can make them conduct—prefer DC or spec’d bypass.
Filters with big Y-caps: expect higher leakage; tune trip and ramp.
Paint/oxidation at bonds: zero the surface (bare metal) before retesting.

4.2.10 Data & traceability (attach to the SN)

Recipe ID & version, Class (I/II), operator, timestamp.
Earth Bond: current, worst-case Ω, points tested.
IR: voltage, dwell, MΩ per pair.
Hipot: AC/DC, voltage, ramp/dwell, trip setting, max leakage, pairs tested.
Leakage (if run): value + condition (normal/single-fault).
Fixture/tool IDs and pass/fail decision. No manual edits—MES only.

4.2.11 Acceptance cues (10-second tour)

Area	Accept	Reject
Earth bond	≤ 0.10 Ω to all metal	High Ω, paint under washer
IR	Stable high MΩ	Drifting MΩ, moisture/contam
Hipot	No trip at spec; clean discharge	Trip, audible arcing, no discharge wait
Leakage (if run)	Within recipe limit	Over-limit, noisy unstable reading
Safety	Door interlocked; strap OFF	Open-door tests; strap on

4.2.12 Common traps → smallest reliable fix

Trap	Symptom	Fix
L & N not tied for Hipot	Inconsistent stress	Tie L+N together for primary tests
Testing with ESD strap on	Shocks, weird fails	Strap OFF for HV; post a sign on the cage
MOVs/Y-caps tripping AC Hipot	False FAILs	Use DC Hipot + ramp; or enable design bypass
Paint under earth lug	High Ω	Scrape pad, serrated washer, re-torque, measure
No discharge wait	Zaps when opening	Enforce bleed-down <30 V interlock
“Copied limits” from other SKU	Wrong calls	Versioned recipe per SKU/Variant
Bond only at one panel	Floating lids, ESD pain	Bond every metal subassembly <0.1 Ω

4.2.13 Pocket checklists

Before

SKU/Variant scanned → correct safety recipe loaded
Interlock/E-stop OK; strap OFF; leads/labels checked
PE pads bare; serrated washers installed where called

Run

Earth Bond: ≥10 A; worst point ≤0.10 Ω
IR: 500 VDC; MΩ within limit
Hipot: pairs per recipe; ramp/dwell/trip set; discharge
(If required) Leakage: mains on; values logged

Close

All results to SN in MES; no manual edits
Fails to NG-QUAR with pair/step noted
Cage tidy; daily self-test tile green

When safety testing is executed with discipline and precision, products leave the line compliant, safe, and ready for global shipment. The reward is confidence—in audits, in the field, and in every customer interaction.