Amprobe ACD-330T Clamp-On-Multimeter - Manual (Page 38)

1. The AC neutral wires must be of sufficient gauge to allow for harmonic current.
2. The distribution transformer must have additional cooling to continue operation
at its rated capacity. This is because the harmonic current in the secondary neutral
wire is circulating in the deltaconnected primary winding. This circulating har-
monic current heats up the transformer.
3. Phase current harmonics are reflected to the primary winding and they continue
back towards the power source. This can cause distortion of the voltage wave so
that any power factor correction capacitors on the line can be easily overloaded.
We can use this Meter to analyze components such as power distribution trans-
formers and power factor correction capacitors. An additional feature allows the
measurement of half-cycle peak current by using the 1 ms peak hold feature. This
allows the ability to determine crest factor:
Crest factor = Peak value/True rms value
NOTE: If Crest Factor exceeds 1.1, harmonic distortion is present
TRUE RMS MEASUREMENT
The meter measures the TRUE RMS value of AC voltages and currents. In physi-
cal terms, the RMS (Root-Mean-Square) value of a waveform is the equivalent DC
value that causes the same amount of heat to be dissipated in a resistor. TRUE RMS
measurement greatly simplifies the analysis of complex AC signals. Since the RMS
value is the DC equivalent of the original waveform, it provides a reliable basis for
comparing dissimilar waveforms.
By contrast, many meters use average-responding AC converters rather than TRUE
RMS converters. The scale factor in these meters are adjusted so that they display
the RMS value for a harmonic-free sine wave. If a signal is not sinusoidal, average-
responding meters do not display correct RMS readings.
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