Electrical Clearance: Determined by Voltage
The electrical clearance (spacing between live parts) for complete electrical assemblies is determined by voltage level: 10–20 mm for low voltage (380 V), 125 mm for medium voltage (10 kV), and 300 mm for high voltage (35 kV). These specifications are based on GB/T 7251 (low voltage), GB/T 3906 (high voltage), and IEC standards.
Industry experts note that clearance requirements should be verified against the relevant standards: low-voltage distribution cabinets (GB/T 7251: clearance between live parts and earth/between phases depends on voltage) and high-voltage cabinets (GB/T 3906: based on rated voltage and altitude correction).
Electrical clearance (to prevent discharge) is designed and inspected according to these standards.
Clearance Requirements (Reference)
- Low voltage (380 V): Clearance between live parts and earth/between phases is 10–20 mm (per GB/T 7251);
- Medium voltage (10 kV): Phase-to-phase/phase-to-earth clearance is 125 mm (per GB/T 3906);
- High voltage (35 kV): Clearance is 300 mm (clearance increases as voltage rises);
- Altitude correction: Clearance must be increased for high altitudes (>1000 m) due to air density;
- Creepage distance: Verified separately based on the creepage distance ratio (pollution level);
this differs from electrical clearance.
Key Points
First, consult the standards.
Consult the relevant standards (GB/T 7251/3906) to determine clearance distances and prevent insufficient spacing.
Second, apply altitude correction;
increase clearance for altitudes above 1,000 meters to prevent electrical discharge.
Third, conduct acceptance measurements;
verify clearance upon delivery to ensure specifications are met.
Fourth, distinguish between clearance (air gap) and creepage distance (surface path) and verify each separately.
Pitfalls to Avoid
First, “insufficient clearance” (risk of discharge/breakdown);
ensure designs comply with standards.
Second, “ignoring altitude” (risk of discharge);
apply altitude corrections to clearance distances.
Third, “omissions during acceptance”;
ensure clearance is measured and verified during the acceptance process.
Trends and Reminders
Switchgear is trending toward miniaturization, characterized by compact designs (optimized clearance) and enhanced insulation (solid insulation).
Designers are advised to “design according to standards, apply altitude corrections, and conduct acceptance measurements.”
Adhering to clearance standards ensures insulation safety and reliability.
