I am attempting to read the current from this CT using my DMM. The setup connects a desktop heater to a extension cord I made that exposes the live wire. I use my DMM to take a measurement clamps one of the probes on the sleeve (-) and the other probe on the tip (+).
Our voltage is 120V.
My expectation is to get a reading in the mA. Something like 6 mA. What I am getting is 6uA. 6uA is way too low. Am I not measuring correctly?
Hmmm… That’s not what I thought (so I don’t understand). I have my “extension cord” plugged into my 120V socket. plugged into that is a heater which is about 1200w. I put the CT on the black (live) wire. I put the DMM probes on the sleeve and tip of the 3.5 TRS. Given that V = 120V and P = 1200w, P = IV, I = P/V, I = 1200/120 = 10A. The CT has 1800 coils. So I expect 10/1800 = 5.6mA?
That’s meaningless. (Because the manufacturer will tweak the number of secondary turns to give the best accuracy overall.) The ratio of a c.t. is ALWAYS specified as a ratio of two currents, the rated primary current to the corresponding secondary current. So your SCT-013-000 is 100 A : 50 mA. And that also tells me that the maximum current you can measure is 100 A.
Therefore reworking your maths:
Primary (load) current is 1200 W ÷ 120 V = 10 A (correct)
Secondary (meter) current is 10 A × 50 mA ÷ 100 A = 5 mA.
So you were close - but far enough away to get confused by the discrepancy.
If you’re not measuring that (within a few percent), there’s either a problem with your c.t., your connections (but you’re measuring at the right place - tip and sleeve), or your meter (or the range you’re using - those pictures are blocked to me, so please upload them here if they’re meaningful).
All I can say is, whenever I’ve measured a c.t. that way, it gives the right answer for me.
Meter fuses can be a source of great danger. You must NEVER rely on a no-voltage indication by a meter unless you have proved that the meter is indicating correctly both before and after the zero reading on the conductor under investigation. This is so that you have evidence that the fuse has not blown.
My DMM likewise has separate inputs fused only on the current ranges, but I wouldn’t like to guarantee that every meter does the same. And even so, relying on a no-indication, without proving the instrument, is fraught with danger.