Расчет PE-проводника и защитное уравнивание потенциалов в низковольтных щитах

Адиабатическое уравнение — IEC 60364-5-54

S = sqrt(I² × t) / k

Where:
  S = minimum conductor cross-section (mm²)
  I = fault current, RMS (A) — use prospective short-circuit current
  t = fault duration (seconds) — MCB/fuse operating time at fault current
  k = material factor (see table below)

k values (IEC 60364-5-54, Table 54.2 and 54.3):
  Copper conductor, PVC insulation:          143
  Copper conductor, XLPE/EPR insulation:     176
  Copper conductor, bare (exposed to touch): 228
  Aluminium conductor, PVC insulation:        95
  Aluminium conductor, XLPE/EPR insulation:  116
  Steel conduit (as PE):                      51

Worked example — motor feeder PE sizing:
  Prospective fault current: 5,000A (5kA)
  MCB Type D 63A — trips in 0.1s at 5kA (from trip curve)
  Conductor: copper, PVC insulation → k = 143

  S = sqrt(5000² × 0.1) / 143
  S = sqrt(25,000,000 × 0.1) / 143
  S = sqrt(2,500,000) / 143
  S = 1581 / 143
  S = 11.1mm²  → next standard size: 16mm²

  Check: phase conductor for 63A Type D = 16mm² (from IEC 60364)
  Table method: phase 16mm² → PE = 16mm²  ✓ (same result)

Проверка тестовой перемычки TN-S на шине заземления

In TN-S and TN-C-S installations, a removable test link
between the earth bar and neutral bar allows verification:

With test link CLOSED (normal operation):
  - Earth and neutral are connected at MEB
  - Installation is in TN-S/TN-C-S configuration

With test link OPEN (for testing only):
  - Earth and neutral are isolated from each other
  - IMPORTANT: supply must be isolated when test link is open
  - Use to verify: zero volts between N and earth bar
    (confirms no downstream PE/N crossover connections)
  - Measure Zs using a loop tester with N terminal disconnected

If voltage appears between N and earth bar with test link open:
  N and PE are bridged somewhere downstream (wiring error).
  NEVER reclose test link until fault is found and corrected.

PE-соединения в щитах KNX и DALI

Standard MCB/RCBO circuit:
  MCB PE terminal → panel PE bar (via MCB PE terminal block)
  Size: same as circuit phase conductor per IEC 60364-5-54 table

Motor circuit PE:
  Motor PE terminal ≥ motor cable phase conductor cross-section
  At motor: PE connects to motor frame ground terminal
  Star point of motor: connected to N at VFD output (if VFD used)
  For motors with VFD: high-frequency PE cable required (screened
  SY or YSLY-JZ with 360° screen termination at VFD and motor)

KNX bus equipment PE:
  KNX power supply (29V) → PE terminal on PSU case → panel PE bar
  KNX IP router → PE terminal on router → panel PE bar
  KNX TP cable YCYM screen → panel PE bar at panel end only
  (Never earth YCYM screen at field device end — creates ground loop)
  KNX bus conductors (red/black) → NOT connected to PE bar

DALI bus equipment PE:
  DALI gateway → PE terminal on gateway case → panel PE bar
  DALI 2-wire bus (no screen) → no PE connection required on bus
  Emergency ECG battery circuit: SELV — no PE connection

Процедура тестирования непрерывности заземления

Equipment: calibrated low-resistance ohmmeter (microohmmeter)
  NOT a standard multimeter — contact resistance at probe tips
  introduces errors of 0.1–0.5Ω, masking real faults.
  Use dedicated earth continuity tester (e.g. Megger DLRO10)

Test connection:
  1. Connect tester reference lead to panel PE bar
  2. Connect tester test lead to PE terminal of equipment under test
  3. Apply test current (typically 200mA–10A DC)
  4. Record measured resistance

Acceptance criterion (IEC 61557-4):
  Protective conductor resistance ≤ 0.1Ω (100mΩ) total

  Additional check: calculated resistance from conductor length
  and cross-section should match measured value within 20%
  R = ρ × L / A  (ρ copper = 17.2 × 10⁻⁶ Ω·mm²/m)
  Example: 25m of 2.5mm² copper → R = 17.2×10⁻⁶ × 25 / 2.5 = 0.172Ω

  If measured resistance exceeds 0.1Ω:
    - Check all connector terminations (torque, crimps, lugs)
    - Check for corroded connections or damaged conductor
    - Verify conductor route and length (unexpected joints)