Evaluating a Grounding System
Staff -- Consulting-Specifying Engineer, 6/1/2001
The Shuttle Avionics Integration Laboratory (SAIL) in Huntington Beach, Calif., was designed with an isolated single-point earth grounding system, which best simulates a vehicle in flight while protecting laboratory personnel against shock and equipment faults. The test configuration is as close to an operational space shuttle as possible and reduces the electromagnetic interference environment in the SAIL facility. Controls are in place to prevent the isolated single-point grounding system from causing safety hazards.
A new single-power transformer dedicated to the SAIL area was installed to replace three existing transformers and improve the fidelity of both the power quality and the grounding within SAIL. Although this new hardware installation conflicts with the SAIL ground isolation requirements, it conforms to the National Electrical Code (NEC), 1990 edition.
In conjunction with the new installation, engineers from Spencer Engineering, Carmel, Ind., and facility engineers from the National Aeronautics and Space Administration proposed tying the isolation transformer secondary wye neutral as well as the master electrical common connection assembly to the facility ground, thus creating a non-isolated single-point grounding system.
A grounding system evaluation was performed to verify that the new SAIL grounding configuration was electromagnetically compatible. All isolated grounds, even a single-point ground, pose a potential hazard during a lightning strike.
The evaluation examined areas such as effects of the non-isolated single-point ground to the SAIL in terms of electromagnetic interference (EMI). Knowledge of EMI noise under two different single-point ground conditions was a "threshold test" for approving the system.
From Pure Power, Summer 2001.
