Product Description 40A NO-NC Relay This sealed, watertight relay is a great choice for several situations you may find yourself in when working on your boat’s electrical system. It’s a full NC / NO relay – Rated at 30A on the NC circuit, and at 40A on the NO circuit. It has a 12V coil, which means it’s meant to be switched by a controller than operates on 12V. The NO (Normally Open) circuit (blue) is one that is always off (an open circuit is off), unless a 12V is applied to the coil. This would be used when you have a switch that is not rated for the current load of the device. For example: Let’s say you’re using a 10A pushbutton switch, but want to turn on a light bar that requires a 30A fuse. The NC (Normally Closed) circuit (yellow) – and this is pretty cool – “flip-flops” what the control switch is doing. So, when the switch is ON… the relay is OFF (open). And when the switch is OFF, this circuit of the relay is ON (closed). This is needed on things like KILL switches on a diesel engine, where the fuel pump needs a constant flow of 12V until you’re ready to shut it off; at which time that 12V signal is deprived, starving the engine to stall. This 40A NO-NC relay is nice to use in wet environments, because it has a nice waterproof cap with seal – and waterproof wire leads. The wire leads include (2) 16AWG and (3) 12AWG. Connecting these leads with heat shrink butt connectors should make a complete waterproof assembly. Wiring Diagram:
