A DC ground is an insulation fault from either pole of the substation DC system, usually 110 V or 125 V, to earth. The system is designed to run unearthed, so one ground causes no trip but is alarmed by a detector, while a second ground on the opposite pole can operate breakers falsely or stop them tripping. Finding one means briefly removing circuits one at a time while watching the detector, a slow and nervous job.
Positive DC ground alarm at Northgate, 40 kilohms and dropping, start splitting circuits but don't touch the trip supplies without calling me.
Also heard as
- battery earth fault
- DC earth fault
- DC earth
Related terms
IT system
Earthing arrangement in which the source is isolated from earth or earthed only through a high impedance.
Trip
To open a circuit breaker automatically through its protection, or to order a breaker open by command.
Earth fault
Fault in which a live conductor makes unintended contact with earth or with earthed metalwork.