Metering single phase with one CT

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mbrooke said:
IS it possible to meter 120/240 with only on CT?
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It is possible in theory. You run both L1 and L2 through the CT but in opposite directions so that the magnitudes add rather than subtracting.
But this requires you to make the assumption that both 120 legs are equal in voltage and equal to 1/2 the L1-L2 voltage.
That will not be the case if the utility sources is unbalanced or when there is a large voltage drop in the neutral to the panel for unbalanced loads.
The small error that causes will overestimate the actual power delivered.

If your meter is set up to use the L1-L2 voltage times the CT current (with vector product), you will have to divide by 2 somewhere along the way.
 
GoldDigger said:
It is possible in theory. You run both L1 and L2 through the CT but in opposite directions so that the magnitudes add rather than subtracting.
But this requires you to make the assumption that both 120 legs are equal in voltage and equal to 1/2 the L1-L2 voltage.
That will not be the case if the utility sources is unbalanced or when there is a large voltage drop in the neutral to the panel for unbalanced loads.
The small error that causes will overestimate the actual power delivered.

If your meter is set up to use the L1-L2 voltage times the CT current (with vector product), you will have to divide by 2 somewhere along the way.
Click to expand...

So the meter must be wired to L1 to N instead of L1-L2?
 
mbrooke said:
So the meter must be wired to L1 to N instead of L1-L2?
Click to expand...

The potential coil of the meter, yes. Unless it was designed/adjusted to divide by two.
An in line (no CT) meter designed for 120/240 single phase does not even have a connection to the neutral.

But again you are assuming that the L1-N and L2-N voltages are perfectly balanced.
 
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