PM864A PM864AK01 3BSE018161R1 ABB Processor programmable control module

PM864A PM864AK01 3BSE018161R1 ABB Processor programmable control module

PM864A PM864AK01 3BSE018161R1 ABB Processor programmable control module

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It is assumed that the risk of a double earth fault in which the first fault is

downstream of the breaker on one polarity and the second is upstream of the

same switching device on the opposite polarity is null.

In this condition the fault current, which can reach high values, effects only

some of the 4 poles necessary to ensure the breaking capacity.

It is possible to prevent the possibility of a double earth fault by installing a

device which signals the loss of insulation and identifies the position of the first

earth fault, allowing it to be eliminated quickly.

Networks with one polarity connected to earth

As the polarity connected to earth does not have to be interrupted (in the example

it is assumed that the polarity connected to earth is negative, although the

following is also valid with the polarity inverted), the diagram which shows the

connection of 4 poles in series on the polarity not connected to earth may be

used.