4.2 Safety Testing
Hipot, insulation, and grounding verifications.
Safety testing turns a powered box into something safe to touch, ship, and certify. It proves metal parts are bonded to earth—PE (protective earth)—and that insulation really isolates hazardous circuits, not just on paper. Core checks like IR (insulation resistance) and Hipot (high-potential dielectric stress) catch moisture, miswires, and weak clearances before they become shocks or smoke. Class I vs Class II (earthed vs double-insulated) sets the playbook, while guarded fixtures, interlocks, and bleed-down make the process calm and repeatable. Clear limits and clean records make it audit-proof, so safety isn’t a hunch—it’s measured, traced, and trusted.
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)
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)
4.2.12 Common traps → smallest reliable fix
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