Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1985-04-05
1987-12-08
Scott, J. R.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 45, H02H 316
Patent
active
047121513
ABSTRACT:
A system for detecting ground faults in circuit breakers having electronic trip units tied together by a low impedance common or circuit ground conductor. A complete electrical path between two circuit breakers is created when the secondary winding of the instrument current transformer of each circuit breaker is grounded as required by National Electrical Code rules. This can cause the ground fault sensing apparatus to inaccurately reflect the ground fault levels of the circuit breakers. The summing transformer of this invention includes a first primary winding which sums the currents through each of the phase current transformers and a second primary winding which indicates the current through the neutral conductor. The second primary is grounded, the ground does not provide a return path for the current between the two breakers since the second primary is isolated from the other summing transformer windings which are electrically connected to the circuit breaker.
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Golden Larry I.
Guttman Richard T.
Jankousky Mary R.
Scott J. R.
Square D Company
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