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John,
Many of the less expensive CT / AC ammeter setups are nonlinear at the
bottom of the scale. You have to have enough current to get at least 10
- 15% of a full scale reading to make them work accurately. This is
because the meter movement inside the analog meter is actually a DC
movement driven by a diode bridge, and you have to apply enough voltage
to the terminals to overcome a couple of diode forward voltages to get
the pointer to budge. Once the diode bridge in the input circuit is
fully conducting, the readings will be valid.
You said that with both the digital and analog meter connected to the
CT, you got no readings. If you connected all three devices in series
(which is the correct way), no current would flow until you had overcome
the forward voltage of the bridge in the analog meter.
If you are seeing a scale reading of 18 - 23 amps with the analog meter
alone connected directly in your circuit without the CT in place, then
it would indicate that you are actually running 1.8 - 2.3 amps in your
NST primary, since 5 amps would drive the analog meter to full scale,
or the 50 amp position.
If you connect the current transformer to a good quality DMM set on the
10 amp scale, is should be linear down to very small currents.
Dave
On 9/16/2015 8:18 AM, wt5y wrote:
With just the meter inline I'm seeing 18-23amps, with CT and dmm is 14amps, with both its nothing. I don't think the CT is very accurate for such low currents
John cooper from what I read everything is about installing it on busbar
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