Insulation monitor for direct current networks, AI898 Fixed response time 6kΩ LED display for operational readiness and earth fault 1 changeover Overall width 45mm The AI898 insulation monitor displays the insulation resistance of unearthed direct current networks to earth. It does not detect symmetrical earth faults. In practice, these faults are generally insignificant. The AI898 works on the quiescent current principle, for example when the auxiliary voltage is applied to terminals A1 → A2 the output relay is activated and the "ON" LED indicates that the insulation resistance RAN is not less than the minimum value. If insulation resistance falls below the response value, the output relay drops, the "ON" LED goes out and the second LED for "Earth fault" lights up. A bridge between terminals LT1 and LT2 (inserted as standard) allows the AI898 to be programmed for memory storage behaviour; remove the bridge to programme hysteresis behaviour. The bridge can