Meter Set Up Question

[hbendillo]

One of my clients has an Amprobe DM II Pro meter. This meter will measure the current and voltage of each phase and the reports will show phase voltages and currents; real, reactive and apparent power; and power factor.

The amperage clamps are rated for up to 1000 amps and there is one for all three phases of a three-phase system and one for the neutral. The feeder were measuring is rated 1200-amps, 208-volt three-phase, four-wire. The feeder has three conductors per phase.

Because of the way the conductors were attached to the lugs at which were taking the measurements my client could not get the amperage clamp around all three conductors of each phase. They only clamped around one conductor of each phase and neutral. The results were interesting. Where I expected to see probably 200 to 300 amps of phase current the report showed 2000 to 3300 amps. This is roughly three time what I would have expected if we would have been able to clamp around all three conductors. Is there a correlation here? What is the effect of only clamping around one conductor of each phase? Can I extrapolate the actual current on each phase from this?

 

[stevenal]

The effect of clamping around one conductor would be to slightly load that conductor forcing it to carry even less current than it would without the meter present. Sounds like you have the meter set for the wrong clamp (ratio).