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 C60 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).
TSXPSY2600M (see p 2/3 Modicon Premium catalogue 2008)
It = 0.067 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 = 0.067/0.01 --> 6.7 A per power supply.