Safety Checklist

This checklist is prepared to ensure user safety, prevent electrical and thermal hazards, and verify compliance with international safety standards. The goal is to eliminate accidents and risky situations in advance during both production and usage processes.

Fuses and Protection Circuits​

1. Are technical specifications of fuses and circuit breakers on the system defined?​

Fuses used at each power line or energy input point must be technically defined with correct parameters. The following information should be clearly stated in documentation:

• Fuse type: Glass, ceramic, SMD, PTC (resettable), circuit breaker, etc.
• Nominal current rating: Maximum current the fuse can continuously withstand
• Delay characteristic: "Fast-blow" (fast-acting) or "Slow-blow" (time-delay) type
• Operating voltage: AC/DC and maximum operating voltage
• Size and mounting type: 5×20 mm, 6.3×32 mm, 1206 SMD, etc.
• Approved standards: UL 248, IEC 60127, or VDE certification

An incorrectly selected fuse may fail to open in time during overcurrent, causing component burnout or PCB trace damage. Appropriate fuse value should be determined as approximately 125% of the system's maximum continuous current.

2. Are fuse dimensions and characteristic values marked on PCB?​

Near the fuse holder on the PCB, the fuse type and value should be shown with clear labeling. For example: "F1: 250V / 2A Slow"

This information facilitates selection of correct replacement fuse during maintenance and shortens service time. Label should be visible both on silkscreen layer and in technical drawings. Additionally, fuse labels should match definitions in BoM (Bill of Materials) exactly.

3. Can fuse installation and removal be performed without affecting other components?​

When fuses need replacement during service or maintenance, surrounding components should not be damaged or block access. For this purpose:

• At least 10 mm access clearance should be left around fuse holder
• Components sensitive to high temperature (e.g., electrolytic capacitors) should be positioned away from fuse
• Holder-type models should be preferred over soldered fuses
• Fuse orientation should be selected close to PCB edge for easy access

This arrangement is important for serviceability and evaluated as ergonomic safety criterion in UL / TÜV field audits.

4. Is there electric shock risk during fuse or circuit breaker replacement?​

User or technician should not be able to directly contact live lines while replacing fuse. Therefore:

• Fuse area should be surrounded by insulating enclosure or plastic protective cover
• In high voltage circuits, 2.5 mm clearance and 4 mm creepage distance should be maintained
• Fuse should be positioned to be accessible only when device is de-energized (e.g., when power cable is disconnected or under rear cover)
• If necessary, warning labels like "⚠️ Do not open while energized" or "Disconnect power before servicing" should be added

Electrical Safety​

5. Are high voltage areas defined?​

All lines on PCB or system above 50 V AC or 60 V DC should be considered high voltage areas. Design and marking rules for these areas should be as follows:

• High voltage areas should be clearly marked with "⚡ HIGH VOLTAGE" label
• These areas should be physically isolated to prevent user access (e.g., plastic enclosure, transparent protective cover, or inner case)
• On PCB, minimum 6.4 mm creepage and clearance distance should be maintained between high voltage traces (IEC 60950-1 Class II limit value)
• Isolation between power and signal layers should be supported with slot cuts or keep-out zones

These measures not only prevent electric shock but also prevent arc formation in high voltage areas due to moisture, dirt, or conductive dust.

6. Are user warnings added for high voltage areas?​

User awareness of high voltage presence on or inside device is mandatory for Human Factors Safety.

• Warnings should be used as labels, icons, or manual notes
• Warning language should be brief, symbols universal
• Example: "⚡ High Voltage – Do Not Touch"
• Warning locations: Power input area, high voltage module cover, service access panel, or screw point
• In manuals, these warnings should be specified visually under "Warning" or "Danger" headings

Properly positioned safety icons are a basic awareness measure that reduces electric shock risk by up to 70% (IEC 82079-1 requirement).

7. Is grounding connection (PE/GND) defined for all metal body parts?​

In all systems containing metal case or mechanical parts, Protective Earth (PE) must be present. This connection protects user from possible leakage current and provides system balance for EMI.

• All metal body parts (e.g., case, cover, mounting brackets) should be connected to PE line with appropriate gauge conductor
• Grounding point should be clearly indicated in drawings with PE symbol (⏚)
• In grounding through screws or washers, contact-free area should be left under paint or coating
• Cable gauge used should be capable of carrying at least 50% of system nominal current
• Protection ground should be connected to signal GND line only from single point (star topology)

Lack of grounding causes leakage current, chassis voltage, and EMI noise.

8. Are protection devices (TVS, MOV, varistor, etc.) correctly positioned?​

Protection elements against overvoltage surges (surge, ESD, EFT) are the system's "front line defense." Positioning is as vital as proper selection of these elements:

• TVS diodes, varistors, or MOV elements should be placed closest to input points (e.g., DC jack, terminal block, USB port, RJ45)
• To reduce high-frequency pulse effects, trace length between noise source and protection element should be less than 5 mm
• Protection circuit should be positioned after fuse; thus when fuse opens in failure condition, voltage line is isolated
• Protection elements against ESD should be applied symmetrically on all lines of external connectors

9. Is fuse/protection circuit coordination (selectivity) ensured?​

In systems with multiple protection elements, sequential operation (selectivity) of these elements is critically important. Incorrect sequencing can cause cascading failure or unnecessary circuit interruption.

Protection hierarchy is typically defined as follows:

1. Primary protection: Fuse or circuit breaker
2. Secondary protection: PTC, TVS, varistor, or transorb diode
3. Tertiary protection: Current limiting resistors or RC snubber circuits

Fuse is responsible for breaking high energy events; TVS and varistor are for suppressing fast transient pulses. In selectivity tests, response time and power endurance of each protection element should be verified. Properly configured protection chain guarantees both device safety and user access safety.

Thermal Safety​

10. Are components generating high temperature identified?​

In every circuit containing power electronics, certain components naturally generate high temperature. Elements like regulators, MOSFETs, resistors, inductors, and transformers can create temperature points exceeding 100 °C during operation. Therefore:

• All temperature-generating components should be marked on thermal analysis or thermal map
• On critical components (e.g., LDO, DC/DC, MOSFET), measurement points should be determined and monitored with PCB thermal sensors (NTC / TC)
• If necessary, temperature limiting components (e.g., thermal switch, PTC) should be added
• Product's nominal operating temperature should be documented (e.g., "Ta: 25–70 °C, Tc: max 105 °C")

11. Are high temperature areas protected from user contact?​

User contact with a hot surface on device's outer surface or service access area creates burn risk. This risk should be reduced with both mechanical and design measures.

• External surface temperatures should not exceed 45 °C (metal) or 60 °C (plastic) limit (IEC 60950-1)
• Areas containing hot components should be physically separated from user with grille, protective cover, air duct, or thermal barrier
• Air flow inside case should be directed to prevent heat accumulation (e.g., fan, diffuser, natural convection)
• In user-accessible areas (e.g., power input, port perimeter), protection should ensure contact distance exceeds 10 mm

12. Are warning notifications added for high temperature areas?​

Informing user about hot surfaces is a mandatory visual safety measure. These warnings should appear both on device and in user manual.

• Device should have "⚠️ Hot Surface – Do Not Touch" phrase and triangular thermal warning icon
• Labeling should be done with UL 969 approved heat-resistant material
• In user manual, this area should be indicated as "CAUTION: Hot Surface" and linked to maintenance instructions
• Warning labels should be placed at points where temperature level is meaningful to user (e.g., cooler, transformer cover, metal enclosure)

13. Is electrical isolation of cooling surfaces ensured?​

Coolers can carry electrical potential while dissipating heat from high power components (e.g., MOSFET, IGBT, regulator). Therefore, safe isolation should be provided for user and other circuits.

• Coolers should be mounted so they do not directly contact drain/collector pins of components
• Mica insulator, silicone pad, or thermal film should be used for electrical isolation
• Insulating bushings (shoulder washers) should be preferred in screw mounting
• If coolers are connected to chassis, low impedance grounding (PE) should be done through connection points
• Insulation resistance should be above 100 MΩ @ 500 V DC level (IEC 61010-1 Section 6.3.2)

This approach is a critical design principle for both electrical safety (shock protection) and fire safety (fire prevention).

Environmental and Mechanical Safety​

14. Has product been examined according to relevant safety standards?​

Safety standards applicable to product according to target market should be determined and conformity assessments conducted.

• Consumer electronics: IEC/EN 62368-1, UL 62368-1
• Industrial control systems: EN/IEC 61010-1
• Office and IT equipment: IEC 60950-1 (replaced by 62368)
• Automotive / heavy industry: ISO 16750, ISO 26262 (with ASIL classes)
• Medical devices: IEC 60601-1

For each product, applicable standards should be added to technical specification (Product Safety Plan) before production and test plan created accordingly.

15. Are applied safety standards documented?​

Which standards tests were conducted according to and obtained results should be documented. For each test, the following information should be recorded:

• Code and version of applied standard (e.g., IEC 62368-1:2020 Ed.3)
• Test laboratory name and accreditation number (ISO 17025)
• Test report number, date, and result summary
• Certification body reference (e.g., TÜV, UL, Intertek)

Certificates should be archived in easily accessible format in documentation section (Compliance Dossier).

16. Is liquid and dust protection (IP ratings) provided?​

IP (Ingress Protection) level should be determined according to product's operating environment and verified with tests.

• IP54: Limited protection against dust ingress, resistance to splashing water
• IP65: Dust-tight, resistant to low-pressure water jets
• IP67: Dust-tight, resistant to brief water immersions (1 m / 30 min)
• IP68: Continuous underwater operating conditions
• IP69K: High-pressure steam cleaning environments (automotive, food industry)

Application examples: Outdoor sensors → IP67, Factory control panels → IP54, Agricultural or humid environment devices → IP65

In protection-oriented design, gasket, sealing material, cable entry gland, and cover tightness tolerances should be considered.

17. Have protection tests against external substances (oil, chemical, moisture) been conducted?​

If oil, solvent, salt, or chemical vapor exists in product's usage environment, material selection should be appropriate for these conditions.

• Oil resistance: Appropriate gasket materials like NBR, FKM (Viton), EPDM should be selected
• Chemical resistance: PC or PBT-GF can be used instead of ABS
• Coating: Conformal coating (acrylic, silicone, parylene) should be applied for PCB
• Moisture resistance: Should be verified with 85 °C / 85% RH tests (JEDEC JESD22-A101)

Additionally, surface paint and label materials should be tested according to ISO 2812 (Chemical Resistance) and UL 969 (Label Adhesion) standards.

18. Have vibration, shock, and drop resistance tests been applied?​

Product should be tested against mechanical stresses it may experience during transportation, assembly, or field use.

• Vibration Test: IEC 60068-2-6 (Sine Vibration) or MIL-STD-810G, in 5–500 Hz range
• Shock Test: IEC 60068-2-27, 15 g – 11 ms, in 3 axes
• Drop Test: ISTA 1A (for packaged product) or MIL-STD-810H Method 516.8
• Body Torsion Test: To measure mechanical durability (especially for long chassis boards)

Vibration and shock tests are mandatory in CE/UL approval processes especially for mobile, industrial, and field-mounted products.

General Safety and User Interaction​

19. Are user warning labels and symbols correctly placed?​

Warning symbols and labels on product are an integral part of design in terms of visual accessibility and semantic consistency.

• Labels should be located at points easily noticed by user (e.g., power input, hot surface, maintenance cover)
• Text should be readable; minimum 2 mm character height, high contrast (black/yellow or white/red) preferred
• Symbols should be selected in compliance with ISO 7010, IEC 60417, or ANSI Z535.4 standards
• Label material should be resistant to environmental conditions (against heat, UV, and solvent)

20. Does user manual contain safety instructions?​

All instructions directly affecting user safety should appear in manual in clear, simple, and action-oriented format.

Example phrases:

• "⚠️ Disconnect device plug before servicing."
• "❗ Only authorized service personnel should intervene."
• "🔥 Do not operate device in unventilated environment."

Instructions should be brief, direct, and in imperative mood. Warning levels should be categorized with "Caution / Warning / Danger" hierarchy. In manual, safety symbols should be given with explanations.

21. Is deactivation or power shutdown procedure defined for emergencies?​

Each device should be able to be safely de-energized in emergency situations. This is mandatory for both operator safety and system protection.

• Hardware should have Emergency Stop or Power Off mechanism
• Stop button should be red and positioned closest to user access
• Alternatively, power line should be cut with quick-response fuse or AC input relay
• In manual, emergency procedure should be defined step by step

22. Are appropriate warning symbols (⚡, 🔥, ☣️, etc.) used on product?​

Symbols are the most effective way to inform user directly and universally.

• ⚡ Electrical hazard → High voltage or leakage risk
• 🔥 Hot surface or fire risk → Power modules, regulator areas
• ☣️ Chemical hazard → Battery, accumulator, or solvent contact risk
• 🧤 Protective equipment use → During assembly or maintenance

Symbols should comply with color coding:

• Yellow triangle → Warning
• Red circle → Prohibition
• Blue square → Mandatory action

23. Has functional safety standard (IEC 61508 / ISO 26262) requirement been evaluated?​

If product is part of a safety-critical system (e.g., motor control, battery management, medical device), functional safety evaluation should be conducted.

• IEC 61508: Basic framework for general industrial systems (SIL 1–4)
• ISO 26262: Automotive safety lifecycle (ASIL A–D)
• In requirement analysis phase, risk probability and impact levels should be calculated
• Failure modes (FMEA) and probability calculations (PFH, PFD) should be documented

This item ensures product's safety functions are systematically verified.

24. Are ASIL / SIL targets and safety case created (if required)?​

If functional safety standard is applied, Safety Goal and Safety Case created to achieve it should be prepared.

• Target safety level (ASIL/SIL) should be determined for each safety function
• "Safety Case" document contains analysis, testing, evidence, and traceability
• Safety architecture (redundancy, watchdog, safe-state) should be supported by this argument

25. Is dual protection (redundant circuit / monitor) applied for critical safety lines?​

Single point failure should not compromise system in critical safety lines.

Dual protection examples:

• Two-relay energy cutoff circuit (redundant path)
• Main processor + safety monitor MCU (supervisor)
• Dual-sensor / cross-check architecture

In these systems, "Fail-Safe" or "Fail-Silent" behavior should be defined. Redundancy is mandatory especially for ASIL C/D or SIL 3/4 levels.

26. Are label / pictogram language and localization controls completed?​

If product is sold in multiple countries, all warning labels and manual pictograms should be translated to local language.

• All translations should be reviewed for technical accuracy
• Language-based symbols (e.g., "Dikkat", "Achtung", "Caution") should be checked for cultural meaning differences
• Label prints are verified according to local legislation in CE / UL audits (e.g., 24 official EU languages accepted in Europe)

27. Are EMC and temperature tests included in safety certification scope?​

Many products cannot receive safety approval without electromagnetic compatibility (EMC) and thermal test results.

• EMC tests (EN 55032, EN 55035) verify device's immunity to interference and emission level
• Temperature tests (IEC 60068-2-2, -14, -78) evaluate overheating or insulation degradation risks
• Results of these tests should be added to safety certification file (Technical Construction File)