Lousy Power? Or Lousy Voltage Probes?

When is a voltage problem an actual case of poor power quality, and when is it instrumentation?

We received a data set this morning that seemed, on first glance to have spectacularly bad power.

Voltage Probe RMSPhase AB voltage is marginally high (500 Vrms, for a 480 Vrms source) but Phases BC and CA show serious issues with voltage level, sags, and waveform distortion. We rolled up our sleeves.

However, if did not take long to realize we were on a Wild Goose Chase. Specifically, event waveshape graphs show arcing that is typically associated with a loose or intermittent connection, but no apparent impact on load current.

Voltage Probe Event 1More damning, zooming out to the RMS level shows very significant shifts in RMS voltage on Phases B-C and C-A, with absolutely no change in RMS current.

Voltage Probe Event 2We’re sending this one back to the client to review. We might still be able to pull out a bit of analysis based on Phase A-B only – but it will be very limited.

One of the benefits of having a live human being performing your power quality analysis – we spot these things in a way that automated report writers can not!