Installing and moving CT’s

Support
1

I have my base system temporarily installed with 4 CT on test circuits. 10 more CT are on order. When the new CTs arrive, I want to move the existing CTs to different ports on IotaWatt. I’ve read in several places that CTs cables should not be unplugged “for any length of time” while on a live wire. Does this mean I have to open the CT before I remove the plug? Or turn off the circuit breaker so there is zero current flow? Or can an active CT be unplugged from IotaWatt “for a short period of time”? 15 sec? for 5 minutes?

I’ve also read that a CT should be shorted if not connected to a load. Does that mean all 3 connectors (Tip, Ring, Sleeve) should be shorted together? Would it be better to solder in a burden resistor (say 20 ohm)? If a resistor is added, which 2 points should it be connected to (Tip, Ring, Sleeve)? I have more that 14 circuits and may clamp CTs on all the circuits and only plug in the ones that are of interest. The plan is to leave the others clamped on a wire but not plugged into IotaWatt.

thanks
Larry

2

Hi Larry,

It’s true that a CT left open can be damaged because it can develop very high voltage. But the CZts from the stuff shop have what are called TVS diodes - Transient Voltage Suppression. These are zener diodes that conduct at about 5-7 volts. So when the CT is unplugged, the diodes prevent it from developing high voltages.

All that said, belt and suspenders, if you are going to leave a CT unplugged indefinitely, I recommend shorting the tip to the sleeve. I sometimes just wrap a strip of aluminum foil snugly around all three segments. The ring is not connected to anything.

3

Thanks for the clear answers. I’ve ordered a 10 pack of Stereo Female 3 pole Audio connectors and will just solder all 3 lugs together. Aluminum foil wrapped around a male plug inside an electrical junction box probably would not pass inspection. I’ve also ordered several headphone splitters to try to double up some CTs into one port on the IotaWatt.
larry