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How can I choose the electrical protection of a PLC?

The circuit-breaker must protect the PLC against high inrush currents on power-up and overloads during nominal operation.
  • Magnetic protection (inrush current on starting) is provided by a iC60 Curve D circuit-breaker (see below for the choice of rating).
  • Thermal protection must be provided by a thermal overload relay rated at the transformer secondary In.

Selection of circuit-breaker:
In the power supply module characteristics, it is the It current on activation that interests us (for each type of power supply). 

Example:
BMXCPS2000 (see product datatsheet)
It = 0.06 A at 240 VAC [Inom = 0.31 A]
The important operating point is located 10 ms into the circuit-breaker trip curve.
At 10 ms, we have an Iinrush = It/10 ms = 0.06/0.01 --> 6.0 A per power supply.
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