Confused with odd readings - resolved

Hey all,
I’ve had my IotaWatt installed for a few months and have just ordered another one to monitor my garage!

I’m in Canada and have a 240V stove, when I subtract its usage from the mains, it looks like the subtraction is correct, but there is still some residual wattage in the graph.

I connected the CT so that one phase is going straight through, and the other phase is going through the CT backwards. I assume that I have something connected wrong, or configured wrong. Thanks for any help!


Here’s my status page as well.

This looks like a configuration issue. I can see that you are using a YHDC SCT013-xxx CT for the stove. 10+ kW is a large load, at least 40 Amps. I question if that is the actual stove usage.

I see that you have an SCT013-xxx CT on the stove. Can you post your inputs setup display so I can see how these are configured?

Also, can you verify the model(s) of SCT013 that you are using. Only the SCT013-000 works properly.

A picture of the mains with CTs installed would be helpful as well.

I agree, that does seem way too high.
I can confirm that I’m using the SCT013-000 for the mains, but, I just realized that the other ones are all the SCT013 with a 30 amp marking on them not 100 Amp like the mains. perhaps this is my error.

I thought I should try using a separate CT for each leg of the stove to see if that makes a difference, the following graph has them split.

I have my Laundry Dryer doing the same thing using a single CT with one wire passed backwards.

This is the CT on all the rest of the circuits, not the mains.

I just found this post, SCT013-000 compared with other SCT013-XXX - explained
Perhaps I need to get the regular 100 amp CT’s.

Yea, breaking them up won’t help, they are voltage type CTs. The SCT013-000 work OK.

If you want to make the 30A voltage type work, you can try this:

These CTs have 62 Ohm burden resistors inside, so those resistors combined with the IoTaWatt internal burden resistors result in a net burden of 15.12 Ohms. So in setup you can change the burden value for that channel from 20 Ohm to 15.12 Ohm.

That’s not all. For some reason, the voltaqge types have a different turns ration than the SCT013-000, so you need top configure them as generic and specify the turns ratio of 1860 and punt the phase shift to about 3:


With that setup, you should get a fairly accurate reading, although the resolution is not as good as an SCT013-000. IMO these are less than optimum CTs.

While that helped quite a bit, I think I’ll take your non optimal comment to heart and get the correct CTs. I moved around the ECS1050 CTs and found them to make all the measurements perfect.
Unfortunately it looks like you’ve shipped my newest order so I can’t beg you sell me more CTs on that order. Would you recommend any others that I can get online? Could I just purchase the proper 100 amp CTs that I’m using for my mains?