PM856K01 AC 800M PM856 3BSE018128R1 ABB CPU controller

PM856K01 AC 800M PM856 3BSE018128R1 ABB CPU controller

PM856K01 AC 800M PM856 3BSE018128R1 ABB CPU controller

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 Fault a: the fault, without negligible impedance, between the two polarities

sets up a short-circuit current to which both polarities contribute to the full

voltage, according to which the breaking capacity of the breaker must be

selected.

• Fault b: the fault between the polarity and earth has no consequences from

the point of view of the function of the installation.

• Fault c: again, this fault between the polarity and earth has no consequences

from the point of view of the function of the installation.

In insulated networks it is necessary to install a device capable of signalling the

presence of the first earth fault in order to eliminate it. In the worst conditions,

when a second earth fault is verified, the breaker may have to interrupt the

short-circuit current with the full voltage applied to a single polarity and therefore

with a breaking capacity which may not be sufficient.

In networks with both polarities insulated from earth it is appropriate to divide

the number of poles of the breaker necessary for interruption on each polarity

• Fault a: the fault between the two polarities sets up a short-circuit current to

which both polarities contribute to the full voltage U, according to which the

breaking capacity of the breaker is selected.

• Fault b: the fault on the polarity not connected to earth sets up a current

which involves the over-current protection according to the resistance of the

ground.

• Fault c: the fault between the polarity connected to earth and earth has no

consequences from the point of view of the function of the installation.

In a network with one polarity connected to earth, all the poles of the breaker

necessary for protection must be connected in series on the non-earthed

polarity. If isolation is required, it is necessary to provide another breaker pole

on the earthed polarity