Overcurrent and earth-fault protection

Overcurrent and earth-fault — the standard package across all SYMAP^® variants

Overcurrent (50/51) and earth-fault (50N/51N, 50G/51G, 67/67N) are the most common protection functions, present in virtually every bay in MV and LV switchgear. They cover short circuits, sustained overloads and earth faults, selectively coordinated through inverse-time or definite-time characteristics. Directional variants (67/67N) provide selectivity in ring networks, parallel-fed networks and networks with multiple sources.

Overcurrent and earth-fault are part of the base package on all SYMAP^® variants (Y, BC, BCG, ECG, Compact+). The choice of variant depends on the broader application requirements, bay type, motor/transformer/generator specifics, control and communication needs.

Typical applications

Phase overcurrent (50/51)

Instantaneous (50) and time-graded (51) overcurrent for short-circuit protection. IDMT (Standard Inverse, Very Inverse, Extremely Inverse, Long Inverse) and definite-time characteristics.

Earth-fault, residual (50N/51N)

Earth-fault detection through residual summing of phase CTs. Sensitive in solidly-grounded and low-impedance grounded networks.

Earth-fault, dedicated CT (50G/51G)

Earth-fault detection through dedicated CBCT or core-balance CT. High sensitivity for compensated, isolated and high-impedance grounded networks.

Directional overcurrent (67)

Directional overcurrent for selectivity in ring networks and two-side fed lines. VT-based polarisation, forward/reverse zones with separate timing.

Directional earth-fault (67N, 67GS)

Directional earth-fault for resonant-grounded and isolated networks. Ug or residual voltage polarisation, sensitive earth-fault current detection.

Switch-onto-fault and cold-load pickup

Special functions for breaker reclosing onto a fault, and for inrush handling on transformer and motor energising. Coordinated with reclosing logic.

Compact+ or classic SYMAP^®?

Overcurrent and earth-fault protection is part of the standard package across all SYMAP variants. Classic SYMAP^® Y/BC series covers the broader range of complex industrial and grid applications. SYMAP^® Compact+ applies where the same bay requires switchgear control in a compact enclosure, a Protection & Control IED.

Products covering this application

Need detailed technical specifications?

For exact protection function coverage, settings ranges, ANSI device numbers, CT/VT specifications, communication protocols and configuration support, contact our team to receive the relevant datasheet and engineering proposal.

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