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MELSEC-Q
1 GENERAL SPECIFICATIONS AND PRECAUTIONS FOR USE
(b) Measures against inrush current
The actual relay life may be significantly shortened compared to the one shown
in (7)(a), depending on the type of a load connected and the characteristics of
inrush current.
Also, the inrush current may cause contact welding.
Take the following measures to prevent shortening of the relay life and the
contact welding.
• Select a load so that the inrush current will be within the rated current of the
module.
• Connect an external relay that can withstand the inrush current.
The following table shows the relation between the load and the inrush current.
Select a load so that the inrush current (i) and the rated current (io) will be within
the rated switching current specified for the output module used.
The inrush current may flow for a longer time depending on the load.
Load type Signal waveform diagram
Inrush
current(i)/rated
current (io)
Signal waveform diagram
Inrush
current(i)/rated
current (io)
Inductive
load
Approx. 10 to
20 times
Approx. 3 to
10 times
Lamp load
Approx. 3 to
10 times
Approx. 3
times
*1
Approx. 5 to
10 times
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*1: Typical electric-discharge lamp circuit includes discharge tubes,
transformers, choke coils, and capacitors. Therefore, note that the inrush
current may flow 20 to 40 times as large as the rated current in the case of
high power factor and low power impedance.
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