Recommended setup 400A, multiple subpanels


I’m trying to come up with the best plan to make sure I’m not missing anything or buying the wrong setup.

We purchased a house that was used as a elderly home so we have lots of square footage)

So we have 2 phases 400A power coming in from the grid.

In the electrical room where it comes in, it splits off to 4 different subpanels. One 100A that’s 4 feet away, then we have in line fuse box to feed the other panels. One of them is 200A and the two others are 100A. The 200 and the two 100 are pretty far from this room.

the 200A is the panel feeding most of the house common living area, one 100A is feeding the garage, another 100A is feeding an house extension where my computer room and home office sits alongside most of my kids rooms (3 out of the 5) and the last 100A is feeding another extension that we converted into a small 3 1/2 for my in-law.

if someone has any suggestion on how I should tackle energy monitoring with this kind of setup I’d love it, I’m a bit loss at to what the best strategy would be.



What are some of your goals?

Do you want to be able to monitor all circuits? You will almost certainly need multiple units to accomplish this. You didn’t indicate how far was pretty far. There are threads on extending CTs.

Do you just want to see the total for the house? This should be relatively easy but your description of the various uses of the different areas suggests that that you more than that.

Worst case scenario is 4 different base units, basically one for each sub panel.

I should have probably mentioned it :slight_smile:

So having 5 kids and the in-law living in the same house comes with a pretty hefty electricity bill. I already have most of my thermostat switched to stelpro zwave as well as many of the light switches in the common area. I would like to monitor my power usage in order to see where I should prioritize my efforts (and budget).

the distance between the power meter and the in-law panel to the rest is clearly out of reach to just use long wires. the nearest one if I had to guess is around 60ft if I draw a straight line.


Typically there should be one power meter into the building. With that many panels, you might have a metering panel with utility CT’s inside.
Then the power lines would be split at a panel with disconnects. These would then feed each sub-panel.

If that is the case, the main panel probably has buss-bars. Bob has large CT’s that can be ‘whole building’ and monitor the mains at that point.

If your installation follows this, then you can add CT’s and monitor the lines from this central point to each sub-panel.

Using 2 IOTAWatt units would allow for a mains monitoring and then a sub-panel monitoring.
One a more permanant central point monitor, the other a movable single panel monitor.

This starts to get spread out, but if you were to list all circuits on each panel, you could use one IOTAWatt to monitor that panel and determine what are fixed loads and what are, for a lack of a better term parasitic. (I think there is a more common term)
A friend has an ice maker and a freezer. Found that by bagging ice, shutting off the ice maker and then only running it when he was low, was a huge savings. That is what I call a parasitic load. something redundant or wasteful and not needed to be on all the time.

The beauty is that if you monitored the mains on the sub-panel and 8 more active circuits, you would get a real grip on what is needed and what is not.

A lot of this is conjecture, so please give us more information about how the power enters the building and split to the various sub-panels.

I wonder what you did.

I just ordered a Iotawatt unit this morning. I have a tiny version of you problem. When I get there, my plan is using Home Assistant to aggregate values from multiple systems into a single total consumption number there. Probably I could aggregate 2 or more Iotawatt using some other method. But Home Assistant allows me to pull data from different types of systems, if I choose to follow that path in the future.