About the Equipment Phase Clearance

Equipment clearance design specifies the minimum air clearances between live HT conductors and adjacent earthed structures, buildings, and other conductors in a solar plant's switchyard — meeting IS 5613 (Part 2) and IE Rules to prevent flashover under normal and overvoltage conditions.

How to calculate it

1. 1Phase-to-earth clearance in air: 11 kV → 115 mm minimum (IS 5613 Part 2); 33 kV → 320 mm; 66 kV → 630 mm; 132 kV → 1,100 mm.
2. 2Phase-to-phase clearance: typically 1.25× phase-to-earth clearance.
3. 3Sectional clearance (from live part to fence or wall): IE Rules specify minimum 1.8 m for 11 kV, 2.4 m for 33 kV.
4. 4Vertical clearance above ground: IE Rules Rule 77 — minimum 5.18 m for LT, 5.48 m for HT up to 11 kV, 6.1 m for 11–33 kV.
5. 5Apply a safety factor: for the actual installed arrangement, use 1.5–2× the minimum electrical clearance to account for conductor sway, construction tolerances, and future maintenance.

Worked example

An 11 kV switchyard for a 2 MW plant: phase-to-earth air clearance ≥ 115 mm (use 300 mm installed clearance for safety margin). Phase-to-phase ≥ 144 mm (use 400 mm). HT bus to perimeter fence: ≥ 1.8 m (install at 2.5 m). Incoming feeder conductor minimum height above ground: 6.1 m at the lowest point. All clearances confirmed on the switchyard general arrangement drawing before construction.

What you can calculate

• Phase clearance
• IS 5
• IEC 60071
• BIL / SI

Standards & references

Frequently asked questions