Monitoring aggregated 120v/240v subpanel usage

I have a standard US residential 200A service, broken out to a subpanel in a garage apartment that I am now renting out. I want to use my Sense to monitor energy usage for the apartment. A basic install works fine to measure total usage and to do device identification. But there’s no way to see specifically what’s being used by the apartment/subpanel.

Enter dedicated circuit monitoring, which I think solves my problem. If I treat the apartment as a single dedicated circuit, I can see its total usage. The drawback I usually see suggested for using DCM for a subpanel is that Sense may not identify devices behind the monitored subpanel. For my use, though, that’s a feature, not a bug. I don’t care what devices my tenant is using, and don’t want to go into the apartment turning devices on and off to figure out what Sense has detected. I just want to sanity-check total usage.

However I’m not sure how to set this up. I am close to 100% sure the subpanel is wired with both phases and a neutral–I think it has to be to support the 120v and 240v loads in the apartment. That means I can’t use the basic DCM setup of one clamp around one leg. So I either need to use two clamps or the “advanced” method of one CT around both legs, with one of the legs reversed.

Is one or the other of these methods more accurate? I’d prefer to just use one CT so I can save the other to monitor an EV charging circuit (balanced 240v load). But I’ll use both for the apartment DCM if I need to.

Also, reports on the forum are mixed on what behavior I should expect for device detection on the DCM subpanel. If devices are already detected by Sense, I know that I need to merge them into the new DCM entity. But will Sense continue to detect devices behind the DCM, or is it smart enough to filter them out? If my tenant gets a new toaster, I don’t want Sense to add it as “Heat 8” and send me on a wild goose chase trying to identify it.

@Kelsey_Instagrammer ,

You have the right idea and are asking all the right questions. I think DCM is the right way to go but you will need to use both CTs, if you want to get an accurate number with mixed 120V/240V. The single CT approach only really works when the 240V “device” is balanced (no neutral wire).

I have a similar setup to what you are proposing - a floor heating subpanel with multiple heating loops on it. It does have a neutral wire on it with one small 120V loop and 4 large 240V loops, but I have knowingly used only a single CT, because the 120V loop is on so infrequently. I’ll have to look back to see if any of the individual heating loops have been detected - the DCM setup isn’t on my main Sense because the main ones uses the Flex Sensors for Sense Solar.

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Thanks @kevin1 - that’s super helpful.

Can anyone confirm whether Sense will continue to identify devices on a subpanel being monitored with DCM?

Any anecdotal experience/data on accuracy of monitoring mixed 120v/240v with two CTs vs. one CT using the “advanced” method of both wires through one CT?

@Kelsey_Instagrammer ,
I just looked back at my DCM devices on my auxillary Sense unit, and I do have two native Heat detections that correspond to parts of my floor heating sub panel. So, yes, detections can happen, but you can roll those detections into the DCM device to avoid double counting if you find that they are associated with a DCM device.

It looks like this is another recent case of Sense doing a native detection of a pool pump that is already on DCM. So yes - it can happen.

ps: I couldn’t go the double wire approach in a single CT route you are contemplating, because I had too little play in the big fat wires leading to my floor heating subpanel. But the physics says it should be accurate as long as you get the directions/phases right.

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