Abstract: Where a computer system PC board has two separate power planes at different voltage levels and a CPU accesses both power planes, a system for detecting when a CPU will short the two power planes and shutting down the power to the lower voltage plane. The contention prevention circuit consists of a voltage level detection circuit having an input connected to the core power plane. The voltage level detection circuit is connected to the input of a shutdown circuit. Upon receipt of a signal from the voltage level detection circuit indicating that the voltage on the core power plane is greater than that provided by the core power supply, the shutdown circuit disables the core power supply.