Sensors - PA
In the Vigirex / Earth Leakage Relay context, a closed toroid refers to a closed‑core (solid) core‑balance current transformer (CBCT).
Here’s what that means and why it matters.
What is a closed toroid ?
A closed toroid
is a one‑piece circular magnetic core(no opening, no hinge).
All live conductors (L1, L2, L3 and Neutral)
must pass through the centre
of the toroid during installation.
It is used to sense residual current for ELRs such as Schneider Vigirex.
How it works (simple view)
- Under normal conditions:
Sum of currents = 0 - With earth leakage:
Sum of currents ≠ 0 → magnetic flux appears in toroid → ELR trips
Because the core is continuous, the magnetic path is perfectly closed, giving maximum sensitivity and accuracy.
Closed Toroid vs Split‑Core Toroid
| Feature | Closed Toroid | Split‑Core Toroid |
|---|---|---|
| Core type | Solid, one piece | Hinged / opening |
| Accuracy | ✅ Very high | ⚠️ Slightly lower |
| Sensitivity | ✅ Best (low mA capable) | ⚠️ Reduced |
| Installation | ❌ Cables must be disconnected | ✅ Can clamp over cables |
| Industrial standard | ✅ Preferred | ⚠️ Convenience use |
👉 Vigirex systems prefer closed toroids, especially where:
- Low leakage settings are used
- Selectivity is required
- Nuisance tripping must be avoided
Why Schneider / Vigirex Uses Closed Toroids
- Better magnetic coupling
- Lower error and noise
- Stable operation in:
- High current systems
- Harmonic‑rich loads
- Long cable runs
This is important for:
- MCCB / ACB earth‑fault protection
- Fire protection settings (≥300 mA)
- Motor feeders, chillers, UPS supplies
Installation Rules (Critical)
For a closed toroid to work correctly:
✅ All phase conductors AND neutral must pass through
❌ Earth conductor must NOT pass through
✅ No neutral‑earth connection downstream
✅ Correct toroid orientation (P1 → load side)
✅ One circuit only per toroid
Violating any of these will cause false trips or failure to trip.
Typical Vigirex Closed Toroid Sizes
- 30 mm – 80 mm → small feeders
- 120 mm – 200 mm → MCCBs
- 300 mm+ → busbars / large cables
Rule of thumb:
Choose the smallest diameter that comfortably fits all conductors
(smaller toroid = higher sensitivity)
When a Closed Toroid is Mandatory
- New panel installations
- High‑risk fire protection circuits
- Selective earth‑fault schemes
- Compliance with IEC / SS standards
- Sensitive leakage settings (<300 mA)
When Split‑Core is Used Instead
- Retrofit on live systems
- No shutdown allowed
- Temporary monitoring
( Accuracy trade‑off accepted)
