TT system
TT stelsel
Also known as: tt, tt-stelsel-ra, ra-berekening, aardingsweerstand-tt, ra-300ma, tn-c-verbod, pen-geleider-verbod, tn-c-rcd-conflict, pen-onderbreken, ra-grens-tt, tt-stelsel-aarding
TT system: Grounding system with its own local earth electrode at the installation side, separate from the network earth point. Always requires an RCD as main protection.
Practical example
TT system. A detached farmhouse with its own earth electrode outside the supply network uses a TT system and is therefore always equipped with an RCD as main protection.
Common mistake
TT system: Relying solely on a circuit breaker for indirect contact protection in a TT system — earth resistance is often too high to achieve the required disconnection time without an RCD.
See also
Related terms
- TN-S system
- IT system
- Residual Current Device (RCD)
- Main earthing electrode
- Earth electrode resistance measurement
- TN-C System
- TN-C-S system
- Earth Fault Factor (IT System)
- Voltage drop
- Temporary Installation — Exhibitions, Shows and Fairground Attractions (§711)
- Four-Pole Switching of the Neutral (TT/IT Systems)
In-depth guides
- → Earthing and earthing systems (TN, TT, IT)
- → §414 SELV, PELV & FELV — the extra-low-voltage measure
- → NEN-EN-IEC 61557-8 IT system and insulation monitoring (IMD) — first-fault detection
- → §411.6 IT system — disconnection on a second fault (§411.6)
- → §411.5 (IEC 60364-4-41) The TT system — why an installation's own earth electrode makes an RCD mandatory
- → §131 Protection Principles
- → §411.3.2 Automatic disconnection of supply (AUV)
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