Measuring Floating Systems

Although the recorder is very capable of working with single phase floating power systems, it is the engineer in charge who will want to know figures usually not available from the recorder. One such instance is stress voltages.

Connecting the recorder with the usual A, N, and G inputs will not tell if the Va is to be added to the N-G, or if N-G is a portion of Va. Also, if the N-G voltage is above 150VAC then it cannot be read with Power Analysis Software below version 5.00 as this has not been adapted for the full-scale capability of the instrument.

All the above is answered by using "split-phase" mode.

Now for the trick. You need to use two current clamps of the same value, each wrapped around the Live (if there is limited space then clamp one to the Neutral but in the opposite direction). One clamp is connected to channel A, the other to B.

After the recording is done, extract the two power graphs. Using the average values you can plot the amount of stress voltage on A, extent of imbalance of A-N, as well as detect any possible earth faults on the system.