ABB TC514V2 After sales service is provided for the control card of the power supply device

Description

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According to condition (1) to correctly choose the protective device, it is
necessary to check that the circuit-breaker has a rated (or set) current that is:
• higher than the load current, to prevent unwanted tripping;
• lower than the current carrying capacity of the cable, to prevent cable overload.
The Standard allows an overload current that may be up to 45% greater than
the current carrying capacity of the cable but only for a limited period.
The verification of condition (2) is not necessary in the case of circuit-breakers
because the protective device is automatically tripped if:
• I2
= 1.3⋅I
n
for circuit-breakers complying with IEC 60947-2 (circuit-breakers
for industrial use);
• I2
= 1.45⋅I
n
for circuit-breakers complying with IEC 60898 (circuit-breakers for
household and similar installations).
Therefore, for circuit-breakers, if In ≤ Iz
, the formula I2 ≤ 1.45⋅I
z
will also be
verified.
When the protective device is a fuse, it is also essential to check formula (2)
because IEC 60269-2-1 on “Low-voltage fuses” states that a 1.6⋅I
n
current
must automatically melt the fuse. In this case, formula (2) becomes
1.6⋅I
n ≤ 1.45⋅I
z
or In ≤ 0.9⋅I
z
.

The magnetic threshold of the circuit breaker XT1N 160 In160 is set at 1600 A.
If tolerance is 20%, the circuit breaker shall definitely trip if the values exceed
1920 A; the cable is therefore fully protected against short-circuit.
Maximum protected length
The formula (3), when solved for the length, enables the maximum length protected by the protective device to be obtained for a precise instantaneous trip
threshold. In Table 3, the maximum protected length can be identified for a given
cross section of the cable and for the setting threshold of the instantaneous
protection of the circuit breaker against short-circuit:
– three-phase system, 400 V rated voltage;
– non-distributed neutral;
– copper conductor with resistivity equal to 0.018 Ωmm2
/m.
The values on the table below take into account the 20% tolerance coefficient
for the magnetic trip value, the increase in cable resistivity due to heating caused
by the short-circuit current and the reduction of voltage due to the fault.
The correction factors shown after the table must be applied if the system
conditions are different from the reference conditions.