What conditions will a wattmeter indicate a negative power?

A wattmeter indicates negative power when the load is supplying power back to the source, which occurs in scenariOS such as regenerative braking in electric vehicles or when a generator is supplying power to the grid. This can also happen when the current flows in the opposite direction relative to the voltage, typically when the load is disconnected or in the case of reactive power in certain AC circuits. Additionally, incorrect wiring or connections can lead to erroneous readings that may show negative power.