These are massive single pole - double throw (SPDT) sealed relay. It allows the Arduino and a wide range of microcontrollers to control high power sources

Features:

• SPDT Relay
• Activated by an ACTIVE LOW signal (0V) or ACTIVE HIGH (5V) (selectable by jumper)
• 5V relay requires 5mA driving current
• Rated up to 30A@250VAC and 30A@30VDC
• Normally open(NO) / closed(NC) contact
• With Power indicator
• Size:47*36 mm