Contact Protection

Inductive load

• http://digital.ni.com/public.nsf/allkb/E51464DDC448187D86257892000CE344
• esp8266 drive inductive load - http://blog.csdn.net/jackhuang2015/article/details/53241013

Arc suppression

• https://en.wikipedia.org/wiki/Flyback_diode
• Fly back diode - https://en.wikipedia.org/wiki/Flyback_diode

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  Use RC circuit protection