Mains electricity does not feel dangerous until it kills someone. 230 V AC at 50 Hz — India's standard grid — passes through the human body at enough current to cause ventricular fibrillation with less than 100 mA. A 60 W light bulb draws 260 mA. The margin between "safe" and "lethal" is not large. Electrical safety standards exist because the gap between a power adapter that looks fine and one that is one failed solder joint away from putting mains voltage on the USB output is invisible to the person plugging it in. IEC 62368-1 and its Indian counterpart IS 13252 are the detailed engineering specifications that close that gap — and every decision they mandate traces back to a failure mode that has already killed someone.
What Electrical Safety Standards Actually Test
When a certification lab evaluates your mains-connected product, they are not reading through your schematic and nodding approvingly. They are running a structured set of physical tests:
Insulation resistance — measuring resistance between mains-connected conductors and accessible parts (enclosure, screws, output cables) under 500 VDC applied voltage. Expected: >7 MΩ for basic insulation, >14 MΩ for double/reinforced.
Dielectric withstand (hipot test) — applying a high AC or DC voltage between primary and secondary circuits for 1 minute and verifying no breakdown occurs. A breakdown is a flashover, arcing, or sustained leakage current above the failure threshold (~5 mA for production testing, ~10 mA for type testing).
Leakage current — measuring current that flows through a human body impedance network connected between accessible parts and earth, under normal and fault conditions. Limits: typically ≤0.25 mA for hand-held equipment, ≤3.5 mA for class I equipment.
Temperature rise — running the product at maximum load in a controlled ambient (typically 25°C or 40°C) and measuring surface temperatures on transformers, capacitors, windings, and accessible surfaces. Components must stay within their rated temperature class. An electrolytic capacitor rated 85°C operating at 95°C will fail within months.
Creepage and clearance measurement — physical measurement of distances on the PCB and within the enclosure between conductors at different potentials.
Abnormal operation tests — blocking ventilation, simulating component failures (shorted diodes, open capacitors), operating at 110% voltage, and verifying the product enters a safe state without fire, explosion, or electric shock hazard.
IEC 60950-1 vs IEC 62368-1 — Why the Standard Changed
For twenty years, IEC 60950-1 was the global safety standard for information technology equipment — computers, power supplies, network switches, printers. It was prescriptive: it told you exactly what to do ("use a transformer with X mm creepage," "install a 250 V fuse on the mains input").
The problem with prescriptive standards is that technology moves. By the 2010s, IEC 60950-1 was being applied to products that did not exist when it was written — LED lighting, IoT gateways, battery management systems. The prescriptive rules did not always map cleanly. More importantly, engineers were following the letter of the rules without understanding why, which meant novel product architectures fell into gaps.
IEC 62368-1 replaced IEC 60950-1 in 2020 (mandatory transition; 60950-1 withdrawn). It also replaced IEC 60065 (audio/video equipment safety) — merging two standards into one. The fundamental shift is from prescriptive to hazard-based.
IEC 62368-1 uses three energy source classes:
- ES1 — energy level too low to cause injury under any circumstances (e.g., SELV circuits, <42.4 V peak)
- ES2 — energy level that can cause pain or injury but not serious harm under normal conditions
- ES3 — energy level that can cause serious injury or death (mains voltage, high-current battery systems)
Instead of "do exactly this," the standard asks: "what energy sources are present, what are the hazard pathways, what safeguards prevent energy transfer to a person?" Engineers must reason about safety, not just look up a table. This is better engineering — and it requires engineers to actually understand the hazard model.
India: IS 13252 is the BIS adoption of IEC 60950-1 / IEC 62368-1 for IT equipment. Products under the Compulsory Registration Scheme (CRS) for IT equipment must comply with IS 13252. BIS CRS requires testing at a BIS-recognized lab and registration before market access. The technical requirements mirror IEC 62368-1 closely.
SELV — Safety Extra Low Voltage
SELV (Safety Extra Low Voltage) is one of the most important concepts in electrical safety engineering. A circuit is SELV when:
- Voltage does not exceed 42.4 V peak (30 V RMS AC) under normal conditions and under a single fault condition
- The circuit is galvanically isolated from mains by double or reinforced insulation
- The circuit voltage cannot rise above SELV limits due to capacitive or inductive coupling from mains circuits
SELV circuits are safe to touch. No additional protection (insulated enclosure, guarded contacts) is required for SELV-rated outputs. This is why USB ports, Ethernet ports, and the output terminals of a properly designed 5 V power adapter are safe to handle — they are SELV.
The design consequence: your isolating transformer or isolated DC-DC converter must be designed and tested to ensure the secondary side meets SELV requirements under fault conditions — including primary winding short-circuit, insulation failure, and component thermal events.
Creepage and Clearance — The PCB Layout Rules That Come From Safety Standards
These two parameters define the physical spacing requirements on your PCB between conductors at different voltage potentials.
Clearance = shortest distance through air between two conductors.
Creepage = shortest path along a surface (PCB substrate, enclosure wall) between two conductors.
Think of it this way: clearance is the straight-line gap across empty space. Creepage is the path an ant would walk from one conductor to another, staying on every surface it passes.
Why does creepage matter? Dust, moisture, flux residue, and contamination on a PCB surface can form conductive paths. If the creepage distance is too short, a contaminated surface can create a resistive path — which at mains voltage means leakage current, arcing, or fire.
Minimum creepage and clearance values depend on:
- Working voltage (peak or RMS)
- Pollution degree (PD1 = sealed/clean, PD2 = normal indoor, PD3 = industrial/conductive contamination)
- Insulation type (basic, supplementary, double, reinforced)
Typical values for mains-connected design (230 VAC, Pollution Degree 2, reinforced insulation between primary and SELV secondary):
| Insulation Type | Min Clearance | Min Creepage |
|---|---|---|
| Basic insulation | 1.5 mm | 2.5 mm |
| Reinforced insulation | 3.0 mm | 5.0 mm |
| Double insulation (basic + supplementary) | 1.5 mm + 1.5 mm | 2.5 mm + 2.5 mm |
Practical rule: for mains-to-SELV isolated designs, use a PCB slot (routed gap through the board) between primary and secondary sides. A routed slot converts the creepage path through PCB material into a clearance path through air — achieving both minimum clearance and effectively infinite creepage in one feature. This is standard practice on isolated power supply PCBs.
Insulation Classes
IEC 62368-1 recognises three levels of insulation between hazardous energy sources and accessible parts:
Basic insulation — one layer of insulation. Acceptable only when a second independent protection measure exists (e.g., protective earth). Found in Class I equipment with earthed enclosures.
Supplementary insulation — independent insulation applied in addition to basic insulation. Together with basic insulation it forms double insulation.
Double insulation — basic + supplementary. Each layer must independently withstand the hipot test. Class II equipment (no earth connection) must use double or reinforced insulation everywhere mains can be reached.
Reinforced insulation — a single insulation system that provides equivalent protection to double insulation but is one physical layer. Tested to the same dielectric withstand voltage as double insulation. Commonly used in compact isolated DC-DC converters where two separate layers are impractical.
Class I equipment (earthed) → basic insulation + protective earth connection.
Class II equipment (double-insulated, no earth) → double or reinforced insulation throughout.
Class III equipment (SELV supply only) → no mains connection at all.
The Hipot Test — Dielectric Withstand
The hipot test (from "high potential") applies a voltage significantly higher than the working voltage between circuits for a defined period. It is a proof test — it stresses the insulation to verify no weakness exists. It does not destroy good insulation; it reveals defective insulation.
Typical test parameters for mains-connected equipment (230 VAC mains):
| Insulation Type | Test Voltage (AC) | Test Duration |
|---|---|---|
| Basic insulation (type test) | 1500 VAC | 60 seconds |
| Reinforced insulation (type test) | 3000 VAC | 60 seconds |
| Production line test (each unit) | 1000–1500 VAC | 1–3 seconds |
The production test is shorter and at slightly lower voltage to avoid cumulative stress on good insulation across thousands of units. The failure criterion is breakdown (flashover, sustained leakage >5 mA on production test, >10 mA on type test) or arcing.
What the hipot test catches:
- Insufficient creepage/clearance on PCB (flashover at test voltage)
- Transformer insulation defects (inter-winding breakdown)
- Insufficient spacing in connectors between primary and secondary pins
- Contamination bridging isolation gaps (flux residue, solder balls)
- Pinhole defects in insulating tape or sleeving
What it does not catch:
- Long-term insulation degradation (use temperature rise testing and material qualification for this)
- Failures under vibration or thermal cycling (use IEC 60068 tests)
Fusing and Overcurrent Protection
IEC 62368-1 requires appropriate overcurrent protection in the mains input circuit. The fuse must be:
- Rated for the supply voltage (250 V or 125 V depending on market — a 125 V rated fuse must never be used on 230 VAC mains)
- Selected to interrupt fault current from the mains supply (fuses must be rated for the available fault current, typically 1500 A for residential supplies)
- Correctly type-classified: T (time-delay/slow-blow) fuses for inductive loads, F (fast-blow) for purely resistive
PCB-mount polyfuses (resettable PTCs) are not acceptable as primary mains overcurrent protection in most safety standard evaluations. They are acceptable on secondary-side circuits (USB port current limiting, output short-circuit protection).
Practical PCB Design Checklist from Electrical Safety Requirements
Use this during schematic and layout review, before sending a PCB to fab:
- [ ] Primary-to-secondary clearance ≥ 3.0 mm (reinforced insulation, 230 VAC, PD2)
- [ ] Primary-to-secondary creepage ≥ 5.0 mm (or PCB slot routed to convert to clearance path)
- [ ] Mains fuse on live conductor, before any other components, rated 250 V
- [ ] Earth connection to chassis/enclosure for Class I products — low-impedance, direct
- [ ] Transformer meets safety isolation requirements (hipot-tested, insulation class declared in datasheet)
- [ ] Y-capacitors (mains-to-earth) rated X/Y class and limited by leakage current budget
- [ ] X-capacitors (line-to-line) rated X class (X2 minimum for 230 VAC)
- [ ] No 125 V-rated components in the mains input circuit
- [ ] SELV secondary voltage ≤ 42.4 V peak under all fault conditions verified in simulation/test
- [ ] Accessible metal parts connected to protective earth or fully enclosed in double-insulated housing
Key Takeaway
IEC 62368-1 is not a checklist — it is a hazard-based reasoning framework. Know your energy source classes, know your insulation requirements, and understand why creepage and clearance distances exist before you place a single component on a mains-connected PCB. IS 13252 mirrors these requirements for the Indian market. The hipot test is not the obstacle; it is the proof that your insulation engineering is correct. Products that fail hipot have a PCB layout, component, or spacing problem that would eventually cause a field failure or a safety incident.