Why do I get negative power results with Fluke Power Loggers?

When setting up a Fluke Power Logger, despite everything seemingly hooked up correctly, you may notice a negative kW value in the power measurements.

On the 1732, 1734, 1736, and 1378 devices, power can be seen in the “Power” mode. 

On the 1770 series devices, it can be seen on the “Verify Connection” screen. When this happens, the amperage and power measurements are marked in RED to get your attention.

It may also be noticed afterwards when analyzing data in Energy Analyze Plus, especially when working with loggers without a user interface like the 1742, 1746, and 1748.

The current clamps are attached with reversed orientation

The negative value is due to current probes with reversed orientation. Simply put, they’re attached backwards!
Current probes like the i17XX-flex1500 are marked with an arrow, which should match the direction current is flowing. They should point towards the load-side.

The 1770 shows a small logo indicating this, appearing next to each phase's amperage measurement.

If the current probes are attached pointing towards the generator side instead (against the flow of current), the amperage appears to the logger as flowing the opposite direction as expected.

This is not always obvious from a cursory glance at the screen. Our power loggers “correct” for this - the data is still recorded as a positive value. But the reversed current flow is a negative value when used in the power calculation.

The calculation used to create a power value in kilowatts is simply multiplication, so a negative value anywhere in the equation makes the total a negative value as well. Simply reversing the current probes to the correct orientation will fix the issue, and the power values will return to being positive.