Hello: I bought a split core CT from Sparkfun a couple of years back and finally got around to testing it out to try to determine how much power my heat pump uses. First thing I did was cut off the plug on the lead from the CT and installed a connector to breadboard. I used 220 ohm burden resistor and installed the CT on one wire of a heater (to test the circuit). I got 0 volts across the burden resistor (AC scale on the multi meter). I measured the resistance of the CT and it looks like a dead short, 0 ohms. The data sheet says the resistance is 250 ohms. I think I have a bad CT. Should i get another CT or did i screw it up by cutting off the plug?
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Re: CT not working?
I don't think cutting the plug off (unless the CT was on a live cable at the time and it went bang as you did it) is likely to have harmed it. A bad CT is a possibility, but I'd favour a cable fault somewhere - does it look as if the cable has been damaged, or pulled out of the CT? What make and type of CT is it? What type of cable?
Re: CT not working?
Thanks for responding. The CT is a split core 30 A. SCT-013-030. Sparkfun has retired it. I attached a datasheet. After looking at the retirded data datasheet, it appears that the SCT-013-030 out puts a voltage, the datasheet says that there is an internal resistor. Cable looks good.
UPDATE: I looked at the phono plug that I cut off, stripped all the wires off. There is a shield wire around the red and white wires that is soldered to the plug. When I measure the voltage between the shield and the other two cables, I get a reading that seems reasonable. I should not have cut the phono plug off. I will have to solder a pin onto the shield.
Re: CT not working?
We're familiar with those, there is indeed an internal burden resistor. I would have expected the secondary would be connected to the red and white cores, normally the cable screen is not connected.
If you want to look inside, it's quite easy and non-destructive: open the core up, and you'll see two plastic clips retaining the bobbin. Spring those out of the way and push on the cable, and the half-core and secondary winding should slide out. (N.B, three or more hands are useful for that operation.)
The secondary winding is about 100 Ω, the parallel burden should be 66.7 Ω, so I'd expect to see 40 Ω approx looking up the cable.