Still in the process of recommissioning an old EmonTX3.2 and EmonBASE system for US split-phase (whole home) power monitoring. I noticed that I’m getting reasonable readings on one leg of my system, but the other leg (identical model CT) reads nothing or very little power (~ 20W when the other leg is reading >5kW). If I swap the CT connections between power1 and power2, the readings move as expected. I’m pretty sure the CTs are well seated. Is there any other troubleshooting step I could/should try? Do CTs just fail in this sort of fashion? All the wiring on the CTs looks fine…though I suppose I could throw a multimeter on there and take a look.
Appreciate any pointers to figure out where the fault is here!
Which c.t. do you have? C.T’s are generally fairly robust, but if you’ve maltreated one (left it on its cable but with the secondary disconnected, i.e. without a burden or a shorting strap, and pulled a high current through it) it could have died.
I think, if it’s a split-core model, it needs to come off its cable and have the secondary winding resistance measured. If it’s got a mA secondary, anything between a few tens of ohms and the low hundreds is most likely OK, under 10 Ω (unless it’s a 1 A or 5 A secondary) or more than 1 kΩ would be highly suspect.
You also need to suspect the plug and the cable, and any joints therein.
Thanks as always, Robert. I’ll have to pull my panel apart again in the morning to verify, but I’m pretty sure these are YHDC SCT023R (100A) split core models. I’ll take a look at the resistance, pull the known working CT and grabbing a reading from that to verify.
If it is, then I’d expect to see around 100 Ω. Unless there’s a few shorted turns (which you’ll never measure by resistance), it will be either about 100 Ω or a lot different!
But those don’t have a protective zener diode, or an inbuilt burden, so if it’s been on a current-carrying conductor without being shorted or burdened, it might have flashed over.
This morning I took both CTs off the legs, visually inspected them, and tested pin-to-ring resistance. Both CTs tested out at ~ 45 ohms. Putting them back on the legs, connecting them in, rebooting the TX and…things worked. I’m at a loss as to why this persisted across reboots, reseats, etc., but I’m happy with the readings.
Thanks for the advice on this. Hopefully this thread may give help to others investigating their CTs.
Well, it would have done, had you found a problem.
You’ll have to put it down to the law of natural perversity.