Bad CTs

While attempting to install my Sense Home Energy Monitor I received the error “BADCTS”. I am working with the Sense support team on a resolution but I wanted to post about this issue (and later update it with the resolution) with the hope that someone else finds it helpful, as I haven’t been able to find any other reports of this error using The Google.

I was able to select “continue anyway” to proceed with registration of my monitor. I am currently 0% complete in the calibration process. Here’s what I’m showing for signals: Mains: 350W 0W Voltage: 123.8V 123.5V Frequency: 60.0 Hz

Other similar posts lead me to believe that I should be seeing two positive wattages. Without the benefit of subject matter expertise, my assumption is that there’s either something unique about my electrical panel that requires me to attach the CTs in an unconventional manner, or that one of the CTs is defective. Reclamping them had no effect on the readings.

Bear in mind that, as far as I can see, Sense is American, and therefore it might be expecting a single phase 120 – 0 – 120 V supply, rather than the more normal single phase 240 V or 3-phase 240/415 V.

If you’re using two c.t’s, that doesn’t seem to make a lot of sense where you are - unless you have one on your grid infeed and one on a PV (or other) infeed.

Where have you put your c.t’s? We have users there, who don’t normally have problems with OEM monitoring set-ups.

Of course, you can have a faulty c.t. – it’s rare but not unknown. If you have a multimeter, you could, with the c.t. not on any cables, measure the winding resistance (or, if it’s the ‘voltage output’ type, the combined parallel resistance of the winding and burden). I’d expect a non-zero value of anything from the low single digit ohms up to a few hundred ohms.

If you have a multimeter that can read milliamps a.c., you could connect that to the c.t. and put it on a current-carrying cable (you won’t harm the c.t.) - I’d expect only a few milliamps maximum given your 350 W (~ 1.5A) load.

That’s indeed the case. Viz:

Given the connecton to each hot leg, the neutral, as well as a CT on each hot leg,
it’s actually “two meters in one package,” so is monitoring each leg independently. Viz:

@Bill.Thomson I didn’t spot that illustration. The Australian supply is very much like the UK system, so if the instructions don’t cover the Australian/UK system, he needs to speak to his supplier, because I saw a claim it’s good for it.

The Sense Energy Monitor

Available for single-phase, split-phase and three-phase panels, the Sense monitor is an ideal solution for existing infrastructure.

I couldn’t find anything WRT to Aus except for a PC Magazine Australia article.

As you said, he definitely needs to get in touch with the supplier.

WRT three phase operation, the specs say it can only monitor two phases.
They mention specifically the third phase will go unmonitored.

What use is that, if you’ve got and use all three phases?

Yep. Not too smart. Here’s the text from their website:

Sense is designed to monitor traditional homes in North America with split-phase 240V service, but it can also successfully monitor two out of the three legs of three-phase 208V service. It is important that Sense is powered by a two-pole breaker across the two legs that will be monitored, and that the current sensors are clamped around the service mains for the same two legs. The power consumption of any devices on the third leg will not be monitored, but the monitoring capabilities of Sense will be fully operational on the other two legs.

There’s a move here in the UK that new builds will have a 3-phase supply - I think it’s with a eye to EV charging.

Sure sounds that way.

I think the OP is essentially out of luck, as the text above says:

Sense is designed to monitor traditional homes in North America with split-phase 240V service,

I’d be looking for a refund if I were him. :frowning_face:

My quote came from the home page. It smacks of false advertising to me.

Although they do state true three-phase operation isn’t supported:

At the moment, Sense can only monitor two of the three phases in these panel setups. The most obvious limitation right now is that the hardware only includes two sensors for current monitoring and two voltage monitoring wires. While the workaround is to monitor two of the three phases, it is important to realize that this is not an ideal scenario. There will be one phase that is left entirely unmonitored by Sense, and the homeowner must be OK with this.


That info isn’t on the main page. i.e. easily found. I had to use their search function to find it.
(it’s “buried” on their installation and setup page)