0611CT1603

PowerPact B DC Systems

Selection of a dc circuit breaker is based on the type of dc system, the rated voltage, and the maximum short-circuit current at the point of installation.

DC Systems

Distribution

Faults

Fault Comments

Worst Case

Ungrounded Source

Fault B

Isc maximum

Both polarities (positive and negative) are involved in the fault.

Simultaneous faults at A and D or C and E

Either polarity may be involved at voltage V*.

Fault A or C

No consequences.

Faults A and D

or

Faults C and E

Isc max

Either polarity may be involved at voltage V.

Grounded Middle Point

Fault B

Isc maximum

Both polarities (positive and negative) are involved in the fault.

Fault B

Each polarity may be involved at voltage V/2.

Fault A or C

Isc < Isc maximum at V/2

The negative or positive polarity is involved.

Grounded Negative

Fault A

Isc maximum

Positive polarity is involved in the fault.

Fault A

All poles taking part in breaking must be placed in series on the positive polarity. If the negative polarity is grounded, an additional pole must be provided to be used for isolation of the negative pole but not for breaking.

Fault B

Isc maximum

Both polarities (positive and negative) are involved in the fault.

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