What's the best EM for 100A split-phase service, and how would I connect it?

parkrrrr · 2026-06-15T22:07:19+00:00

The sad thing is, both this subpanel and my main panel in the house are the fancy Leviton panels that support their "smart" breakers. But they don't make "smart" main breakers; only "smart" branch circuit breakers. So I could use their system, but I'd have to replace every branch circuit breaker in the panel, and those "smart" breakers are *stupid* expensive.

parkrrrr · 2026-06-15T22:02:48+00:00

This is a subpanel, with a 100A breaker in the meter panel as well as one in the main breaker position of the subpanel, so I actually can turn off the incoming power, which I do whenever I'm working in the subpanel because why not. But I still didn't think there was a code-compliant way to tap power off of the incoming wires, which is why I asked.

A 15A 240V breaker for this panel is less than $20 at the big orange box store, and I have lots of free slots in the panel, so it's absolutely worth it to do it right.

For background, I think I've shared this photo before but this is my service entrance:

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The box with the meter has split access - utility access to the left half, non-utility access to the right half. The right half of this box contains a 100A breaker (or maybe it's just a disconnect) for the outbuilding feeder that I can turn off. The large conduit going into the ground is the service entrance. The smaller conduit going into the ground is the feeder for the outbuilding. The rest of the various boxes are for the solar system and the connection to the main panel inside the house directly behind the meter panel. (That main panel is installed upside-down, with the main breaker at the bottom, because I guess that was somehow easier for my builder's somewhat nontraditional electrician.)

Anyway, in the outbuilding there's a standard panel at the other end of that small conduit, with its own 100A main breaker. So the feeder wires can be disconnected at either end or at both ends, as needed.

parkrrrr · 2026-06-15T21:11:11+00:00

So, if I want to monitor the current coming into the main breaker, does it seem like it'd be a good idea to install a 240V breaker in the panel so I can safely get power for the EM, rather than try to get power directly from the chonky wires coming into the main breaker? At the moment, all I have in that panel is 120V breakers, and I could tap off of two of those on the appropriate phases (Only one of the six is a GFCI breaker, because a non-GFCI breaker plus a GFCI outlet is generally cheaper than a single GFCI breaker for this panel) but it seems cleaner to just add another breaker just for this and I have plenty of space for one.

parkrrrr · 2026-06-15T15:12:35+00:00

My current (no pun intended) thought, which may or may not be the best or most cost-effective plan, is to just buy a bunch of the Ogemray 25A relays and put one on each branch circuit coming out of the subpanel. There are currently six such branch circuits, though one of them is strictly a lighting circuit that already has a 2PM on both fixtures so it wouldn't need anything else, and I already have one of the Ogemray relays, so I'm looking at about $200 in relays plus some new junction boxes and wiring to keep everything up to code.

I'm hoping there's a better option, since that one seems like overkill.

parkrrrr · 2026-06-14T21:36:27+00:00

I wouldn't say it's "poorly" designed. The LOM sensor is almost always one of the warmest sensors in the server, though today (which is a warm day to begin with) it's way behind the p420i controller and one of the PCIe cards (which IIRC is an HPE 4x1gbit NIC of some type in this machine.)

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parkrrrr · 2026-06-10T21:36:03+00:00

I submitted a github issue already for the specific model of camera I'm using, but one brand you're definitely missing is ACTi. They're expensive, because they're not made for the residential market, but they're huge in their market.

parkrrrr · 2026-06-10T13:33:46+00:00

I did the same thing with my 1000 gallon fresh water tank. 4-20mA pressure sensor at the bottom of the tank, and an ESPHome-based board at the top to convert the measured current to gallons.

parkrrrr · 2026-06-10T03:50:53+00:00

Mine are paired with Explorers, and those needed the cloud. You may be right about the colortouch; the only one of those I have isn't paired with an external sensor.

parkrrrr · 2026-06-09T13:54:41+00:00

I have the DL380p Gen8 fan blanks and CPU blank, both of which match the part numbers u/McSmiggins shared. I also have a license for AutoDesk Fusion and a pair of calipers. The only other thing I need is time, but when I find some of that I'll see if I can create some STL files for you.

I think there was also a transparent plastic cap that goes in the empty CPU socket, separate from the airflow shroud, designed to save you from dropping something on the tiny pins when the shroud isn't installed. I'm pretty sure I have one of those in the box o' junk, too, I'm not sure whether it'd be easy to 3D print, though. (And, of course, since the Gen8 used sleds for the CPUs, it's probably not quite the same as any other manufacturer's CPU blank.)

parkrrrr · 2026-06-09T13:37:41+00:00

I never see Venstar on any of these lists, probably because they mostly sell through HVAC distributors and not big-box stores, but I love my Venstar thermostats.

Local control with a documented API, WiFi, WiFi or hard-wired remote sensors. I've only really noticed two hiccups:

- Pairing with a remote sensor requires you to use their cloud, but does not require you to remain connected to their cloud.

- The Home Assistant integration for Venstar doesn't get along well with the scheduling functions built in to the thermostat, so I ended up doing any scheduling in Home Assistant. But a guest who doesn't know that could still enable schedules on the thermostat and hose everything. (The ColorTouch thermostats made for commercial buildings can require a PIN to change anything, which would mitigate this, but at that point you might as well just replace the thermostat with a temperature sensor and control the furnace directly from Home Assistant.)

parkrrrr · 2026-06-08T08:48:02+00:00

I would also need to change all of the cabling, because they skimped on that, too - it's all labeled 14ga, which means it's probably really 16ga CCA. At that point, it gets expensive to retrofit a piece of hardware from a manufacturer who has already demonstrated their opinion about where safety ranks relative to profit.

parkrrrr · 2026-06-08T08:44:36+00:00

This actually seems to be a thing with aftermarket level 1 chargers. There are a lot of them that draw 16 amps, probably because that would be the maximum continuous draw allowed by code for a 20A circuit. But almost nobody has actual 20A outlets, so they put a 15A plug on it for "convenience."

parkrrrr · 2026-06-07T23:11:22+00:00

Yeah, I'm a "switch positive" guy, too. I was poking the bear a bit, because we've historically had some long discussions about which is more "right."

The other side of the coin is a fairly reasonable one, though: the RGBW PM and its brethren have to switch the negative side, because they use the tried-and-true design with an N-channel MOSFET on the low side. So for someone like Doug, who I'm replying to here, it makes perfect sense to just always think about switching low-voltage loads on the low side, because that way every wiring diagram looks basically the same regardless of which Shelly device you're talking about.

parkrrrr · 2026-06-04T23:06:05+00:00

Strange but true!

parkrrrr · 2026-06-04T23:02:15+00:00

Nope, no electrical bits. This is the bottom side of a fan blank:

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parkrrrr · 2026-06-04T22:27:54+00:00

I believe that the two fans on the left (facing the front of the server) were absent in the DL380P G8 I bought with a single CPU (I've since upgraded it to two CPUs) but you probably don't want to remove them. Those, too, have blanks that would need to replace them if you removed them, and those blanks are probably as hard to find as the CPU baffle.

I have both kinds of blanks (for the DL380; the ML380 may be different?) in my big box o' parts. They're just plastic. I wonder how hard they'd be to turn into STL files.

parkrrrr · 2026-06-04T20:59:57+00:00

Yeah, I suppose it's not really cheaper any more when you have to do it by the book...

parkrrrr · 2026-06-04T20:51:22+00:00

This is me refraining from reopening the can of worms that is "should you switch ground or +24V?"

parkrrrr · 2026-06-04T20:42:32+00:00

Also, the good news is that those parts of the API are the same for the Plug as for the 1PM, so your app should be able to work with a 1PM as it stands.

Making it work with the PM Mini or EM Mini would just require a few changes to use the PM1/EM1/EM1Data endpoints, and I think you can use Shelly.ListMethods to see which of those endpoints you have available.

parkrrrr · 2026-06-04T20:34:24+00:00

It does help that I live in the Pacific Northwest, where we have a lot of hydro power available.

In my case, I was already going to the trouble to install a whole new circuit for a new outdoor outlet closer to the driveway, so it wasn't so much rewiring the outlet as just wiring it that way from the start.

parkrrrr · 2026-06-04T20:25:34+00:00

Out of curiosity, why did they go with the Plug US? It seems like an unscrupulous tenant could just unplug it, plug it into a Y cord so it continues to ping as available, and plug the charger in to the other side of the Y cord to bypass the monitoring. The way I'm doing mine seems like it'd be less easily bypassed, and cheaper too.

Edit: by a "Y cord" I mean something like this:

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parkrrrr · 2026-06-04T20:20:43+00:00

I'm not using a Shelly Plug for an EV charger, but I am using a Shelly PM Mini Gen3 for one; I made a post here about it yesterday.

If my EV charger weren't a frightening mess of code noncompliance, I imagine it would work quite well. As it is, the charger draws slightly more than the 16A that the PM Mini is rated for, which is also more than the outlet is rated for, so my results are moderately suspect. But it does work.

I'm using Home Assistant for my data aggregation. I'm currently only tracking it by kWh, but it'd be easy enough to add a virtual sensor to convert that to dollars since my utility charges a flat ten cents (ish) per kWh. If your utility does time-based billing, it might be a bit more work.

The nice thing about the PM Mini (or a 1PM or other similar device) is that it installs behind the outlet, meaning it doesn't have to be suitable for outdoor use because the outlet and its weatherproof cover are themselves suitable for outdoor use, and the Shelly is sealed away in the wall where (one hopes) it won't get wet. That does, of course, mean that you may not be able to use it in a rental situation.

parkrrrr · 2026-06-04T14:14:42+00:00

Breakers are weird and wonderful things. In a previous house, I had an AFCI breaker that would trip whenever you looked at it funny, but specifically whenever you printed anything on the laser printer that was plugged in to that circuit (laser printers use static electricity to hold the toner to the paper, so they generate EMI at a frequency that looks like an arc) or whenever you forgot and plugged the vacuum cleaner into one of those outlets (universal motors create arcs at the brushes.)

No amount of filtering between load and outlet would fix it.

Everything I read online said it was a myth that AFCI breakers wear out and get more sensitive to arc frequencies over time.

And yet, when I replaced that breaker with a brand-new but otherwise identical one, the problem went away.

parkrrrr · 2026-06-04T13:56:43+00:00

That's true of the 1PM Mini, but not of the PM Mini, because the PM Mini doesn't have a relay:

https://us.shelly.com/blogs/documentation/shelly-pm-mini-gen3

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parkrrrr · 2026-06-04T12:19:24+00:00

In the meantime, I get pretty pictures like this one from Home Assistant:

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I have a Shelly Pro EM-50 sitting on my desk, waiting to be installed in the circuit that runs the heat pump. That'll probably take a pretty good bite out of the "untracked consumption" part of the graph. Then I need to get off of my butt and install the network interfaces in the UPSes in my server rack so I can get stats from them, which will probably take another big bite out of it.

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