SQUARE D 40 AMP 10kA 30mA FOUR POLE RCCB RCD TYPE AC 05018 RSD 40034

This Square D RCD measures the electricity going out on the Live wire and compares it to the electricity coming back on the Neutral wire. They should be exactly the same. If there is a tiny difference, the RCD assumes electricity is "leaking" out—perhaps through a person or a faulty appliance—and it snaps the power off in milliseconds.

Breakdown of the Technical Specs:

• 40A (Current Rating): This is the maximum continuous current the device can handle.
• 30mA (Trip Sensitivity): This is the "life-saving" part. If the device detects more than 30mA of electricity "leaking" out of the circuit, it will shut off the power in milliseconds.
• Type AC (Standard AC): Only detects smooth AC leakage.

Why do you need it?

If you accidentally cut a cable or a child sticks something into a socket, a standard fuse might not blow fast enough to save a life. The RCD is much faster and more sensitive, cutting the power before the shock becomes deadly.