Hardware Configuration

I am planning on installing two units and was wondering the best way to configure the hardware.
200amp 120/240

  1. Do both units need to be tied to the main lines? If so, can they use the same clamps?
  2. Do both units need to monitor line voltage? If so, can they use the same transformer?
  3. How is solar monitored?
  4. Any other information would be helpful.



Yes, Yes. You can split the transformer output but it’s important to insure you maintain polarity. The best way to do that is to buy a CCTV power splitter

Up to a 12kW system should be able to simply clamp a 50A CT to one of the inverter output lines.

Two units presents a challenge in aggregating the data. If the solar is monitored by the same unit as the mains, you can get the solar picture and/or upload to PVoutput. To get a complete picture, of the whole house, you need to setup the IoTaWatt to upload data to an external server. IoTaWatt supports influDB and Emoncms for that. More technical users seem to prefer influxDB, and others like Emoncms.

Here is a post from a recent similar install uploading to influxDB.

I would advise first looking closely at what you want to monitor. IoTaWatt has 14 inputs. Two go to the mains, one to the solar, and then you have 11 remaining. Most homes don’t have 11 big loads. I realize that there are a lot of circuits in a US panel, but most of them typically don’t represent any real consumption. There are also ways to aggregate multiple circuits into a single CT and multiple CTs into a single IoTaWatt input. For example, in my kitchen I have two plug circuits, microwave and range-hood. I run all of those conductors through one CT and call it “kitchen”. I have an 8 circuit subpanel that feeds bedroom and bathroom plugs - I have a single CT on that. At the end of the day, they don’t amount to significant usage and I can still see the signatures of individual appliances. That’s 12 circuits covered by two inputs.

So my recommendation is to get one IoTaWatt and see what it tells you. You can get extra CTs and combine them, and if it comes to that, you can always add another IoTaWatt. Keeping everything to one IoTaWatt in a residential setting is much simpler.

Thank you for the quick response. I like the idea of going with one to start and upgrading later if I require more separation.
You mentioned that I would be able to see the signatures of individual loads. Is it possible to monitor a load this way without having a seperate clamp?

For many loads you will be able to identify them in a daily plot of Watts, but you will not necessarily be able to determine the kWh they used during that period for instance. Here is my basement:

You can see my freezer cycling every couple of hours. The baseload after about 8:00 am is mostly some growlights in a basement “garden”, and the spikes between 6 and 8 am are the boiler cycling. There’s some washing machine noise in there as well. Note that except for the boiler, all of these loads are on the same circuit anyway, and you will find that to be the case in your home as well.

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Having just done this one thing I’d offer is to spend some time deciding whether, and if so how, you will hide/protect all the wiring. Are you going to put the devices in some kind of junction or other box, for example, will you use conduit for the cables, and how will the low voltage wires and transformers fit into whatever scheme you come up with.

This also plays into the “get one, add another if you need it” aspect. I am monitoring far more circuits than are really useful (where useful is defined as gaining actionable information that I will use to change something, as opposed to just satisfying my curiosity). You really do not NEED more than one IoTaWatt. But if you WANT more data, changing from one to two is pretty easy logically, data wise, not even terribly expensive – but it can throw a real wrinkle into things like conduit and housing if you went that way.

So spend some time deciding on the physical aspects.

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