A couple of weeks back, I received a couple of emonTX v4s to add to my emonBase platform which I was setting up. One of them is in the garage connected to the main incoming feed, the other is in the room with my heat pump kit.
The CT readings from the emonTX connected to the main incoming feed seem more or less spot on, within about 20W of the consumption on the smart meter, and over the course of the day, the CT measurements are within 500W of that from the smart meter.
However, the CT readings from the emonTX connected to the heat pump seem wildly off. I have a 50A CT clamp on a port configured for 50A, which when the heat pump is idle, seems to be reading 270W when I’d be expecting considerably less. On the heat pump distribution board, there is an SDM120 (not being monitored by anything) and over the course of a day, the readings on the SDM120 are about 3kWh lower than those measured by the CT.
I have tried a different CT, and plugged into a different port, and the readings are still wildly off. I’ve tried the CT on different wires (the main feed from the CU to the DB, the live wire from the breaker to the SDM120, and the live wire from the SDM120 to the heat pump) and all have this 270W reading. I’ve noted that when the heat pump is freshly switched on at the consumer unit and it reads 270W, the additional total household power consumption at the main feed only increases by 80W. I haven’t yet tried connecting a CT to the live wire to the main consumer unit for the heat pump circuit as I don’t want to be messing around in there.
The heat pump distribution board has only two outgoing connections - one to the heat pump and one to the immersion heater (which also powers a plug socket for the Homely system). The CT clamp on this does seem to read correctly (currently reading about 20W).
What might be causing this?
– Edit –
Probably worth noting that I have a voltage sensor on the TXv4 at the consumer unit but not on the one monitoring the heat pump, but given that this ‘overreading’ is only on the distribution board circuit to the heat pump and not to the immersion heater, and the size of the overreading, I don’t think this is the issue.
– Edit 2 –
I only get a reading from the CT when around the live cable, but no reading around the neutral cable?