Nearing limits : warning

Not sure if this came up. Assume a home with a standard 100A split phase mains. Or heck: 200A.

Request #1: as more and more stuff becoming power hungry, etc. a home may tend to utilize almost its full capacity. If one factors in the in rush due to mutilple motors, etc the main breaker may start to trip. So, would it not be great if this product post historical analysis start to determine if a particular home is nearing its stated capacity and sends out warnings? This way a homeowner can plan for an upgrade beforehand. If he is already at utility max capacity (usually 300A) then he can sit back and re look his usage?

Request #2: Almost all residential breakers are specifically built to sustain its max rated load for xx time. In other words, 15A sustained current for (say) 5 minutes. If sense can detect a big current draw and that too its longer than xx minutes it has a potential of overheating a circuit breaker. Case in point: with the deluge of EV charging stations an electrician was telling me cases of breakers overheating has quadrupled. Another case where Sense can do preemptive warnings!!


Interesting - I had talked with Sense a while back about the value of a “virtual circuit breaker” to catch these kinds of power issues. The challenge is that Sense can only really accurately observe what’s happening in the mains and perhaps a couple of instrumented circuits (DCM). Still useful.

In these 2 cases the entire technology should be already there.

For example: at any given time Sense already knows the total current draw. Now multiply that second by second for a week. [i do Machine Learning / Deep Learning for a living]. At this point thru unsupervised learning standard algorithms we have patterns which can be used to determine if reaching limits of main lug tolerance. This can then be sent as a warning to the homeowner.

For the 2nd case the approach again is similar to above but atomic instances are captured over time and patterns established. I don’t know what is being used but if Tensor Flow then its very straightforward. Again alerts can be sent out.

For the 2nd case its important to know deep technical details on capabilities of circuit breakers in terms of sustained currents, testing, etc. as 60% of homes are today using the same company products like QO or Homeline breakers, again this should be very doable.

I am NOT suggesting doing anything automated like tripping the circuit, etc. That has its own issues and complexities including code (NEC) etc.

Just alerting the end user.

The company’s sales team should love this idea BTW. As it gives a notification to end user and then gear up to either replace the panel or buy probablu different breakers. Like for example higher rated AIC?

Here’s a little bit more to ponder - a typical “trip curve” for a circuit breaker, which is a function of current usage and sustain time. This is just an example but gives a view of different sustain time scenarios under which a 100A main breaker would trip.

As for your second scenario, the Sense problem is that it has no idea which circuits (and breakers) a detected device is on nor does it know which devices are together on the same breaker. EVs and HVAC units might be special cases it could handle because they typically require dedicated circuits (often 240V).

It’s not as sophisticated as a breaker trip curve, but you can set “goals” in the Sense app that will push a notification to your phone if you exceed a certain power value. I have one set to trigger at 90A on my 100A service. I’ve never hit it, even with an EV charger, a 12kW steam generator, and electric kitchen appliances.

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These goals are fine. However, that’s an isolated use case where due to a particular atomic instance your load center may hit the 90% mark and you get an alert. The whole concept behind Sense is pattern and usage recognition and using which create identifiable and actionable patterns utilizing the power of machine learning. Thus my suggestion. If Sense can tabulate such instances it’ll be great. The technology is already there. Someone needs to write the code. For example - in an area where I work:

Approximately +1 million bank accounts segregated into clients. A client can have 10 to +10,000 accounts globally. Using machine learning I constantly track these accounts w.r.t. over-draft, interest accured, etc. Then via patterns I can make recommendations to the client’s treasury department on how best to structure these accounts into tiers for example which can and will greatly reduce occurrences of overdraft and get interest.

What I wrote above is +10 times more complex than what I proposed.

@kevin1 Thank you. This helps a lot.
Taking my 1st. case : Now that the curves are known, Sense can start accumulating every time the home hits that curve. For example: at 100A @ 1,000 sec. its envisaged the main breaker will trip. 80% of that will be 80A @ 800 sec. Store : Value #1 with time. Iteratively keep adding the values. Set a time period. If there are 6 stored values in that array of (say) 10 max size with time = 1 month, generate an alert. If within that time, the array gets exhausted - generate an immediate alert.

Taking my 2nd case: You’re 100% correct Sense will never know which breaker as it works off the main lug. That’s fair and square. However, it does know if (for example) there was a sudden sustained current which is +50% of stated load and that too for XX minutes. For a 100A, let’s say Sense detected 50A continuous usage across 1 pole(?), both poles and it’s for upwards of 15 min without any drops. Now, most residential circuit breakers as I’m being told are tested with sustained current only for few minutes at best. Even though here the individual circuit breakers - let’s say 1: 15A, 2: 20A and 1: 30A are involved its still within its individual limits so they don’t trip. But, however they are indeed at maximum and that too for so many minutes. There’s a strong chance of over heat here. Again: its NOT something which trips or breaks a circuit but a warning message to end user.

I think there’s a real opportunity here, but I think of it a little different. This would also be a big investment for Sense.

A lot of people are maxing out their panels as they purchase EV’s. Now we know most people charge their EV’s at night, so panel capacity is theoretically not much of an issue. Except this isn’t recognized in building codes, as there will always be that one person who charges an EV while running everything in the house.

What if Sense had an integration with one of the EV charger manufacturers that would only allow the EV to charge when the panel was working well below capacity? This could help people avoid some very expensive panel upgrades. Of course, I assume it would also require some extensive lobbying to factor this into the NEC.

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Seems like a custom notification field could be generated. Such as XX wattage exceeded over XX time. Obviously if would have to be for the whole service box and not a single circuit such as a clothes dryer, if the dry was on and the AC kicked on or a EV charger and you had it set at 8500 watts for 120 seconds its going to send you a warning but in reality your below 36 amps in a 200 amp box.

Maybe this would be better just added automatically to labs.

There used to be 120% rule in the NEC which pretty much means if you have 200 amp main than all your breakers cant exceed 240amps. However seems like every jackleg working on electric these days has never though about that. They wouldn’t hesitate to pull every 15amp breaker out and put 20 amp ones on 14/2 and run a few 100 amp sub panels out of 200amp panel that was already fully loaded. Then these EV chargers are 40-80amps that people are using for 10 hours at a time.

People also forget when adding solar this matters… the rating of the on the “box” is actually the rating of the busbar. So if you have a 60amp interconnect inverter and you are pumping 60 amps in to that bus and your in a 200amp box with a 200 main., you might end up feeding the bus 200 amps and 60 from the solar and those breakers think every thing is fine … and some point your feeding 2 EV chargers. a dryer and 2 AC units so each of the individual breakers also are fine… but your busbar has 260 amps on it which is 30% over its rating.

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@baivab.mitra, just noticed your reference to TensorFlow. Not sure which ML platform Sense leverages for ML, but the main detection learning type today is unsupervised. You might enjoy reading though what I have learned (and think I learned so far) and help extend the knowledge…

Wow!! I have to go thru this, this weekend. I wish we had better access to Sense Developers.

100% correct. Yep: nice for labs!!

Since we are on a time of use rate with demand, I’d like to see a way to get an alert when power use during peak times exceeds a limit I set. I’m trying to stay below 2kw use during peak hours. The demand charge is $12 in the winter and $18 in the summer, so if the water heater timer dies, if it is in the summer, that’s (5.5 + 2) * 18 or a $112 demand charge. Any way to set this?

Reading the CEO 2021 update this morning, you should have this now: "Many utilities are trying to control energy demand during those peak events with Time of Use billing. We expect that this is a trend that will continue, so we added support for Time of Use billing in the Sense app. With this new feature, the Sense app alerts you when an On-peak rate begins and tells you when it will end. It helps you plan activities like running a dishwasher, charging an electric vehicle or washing a load of laundry when off-peak pricing is lower. " from the sense blog.

Hope this helps a bit.

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All of the electrical “rules” I have hears is that the amount of circuits you run should not exceed 80% of your panel/service capacity. This is based on a formula of possible lights, outlets, and major appliances, all drawing at load against the panel. As long as you stay in spec on that you will not have any pull heavy enough to trip the main breaker. All of the other breakers should trip individually long long before you get to the point where the draw is large enough to trip the main. Each one that tripped would reduce that pool again the main so it should be a zero sum issue.

Personally, I have 200amp service in to my main panel and run a 50a and 100 a sub-panels. I do have an EV as the only circuit on one of the sub-panels. with a commercial grade 50a breaker and my EV pulls a max of 32a of the spec’d 40a (80%) rating… most of the breaker “overheating” the electrician referenced is more likely due to using a breaker that while rated for the 30a, 50a or 60a draw, they are using a very cheap non commercial version that while it can hold the load, the draw over multiple hours is not something that breaker is rated for.

Even in the summer where I have 2 AC’s my EV and electric oven pulling current at the same time, I have not gotten close to 80% of my 200A service.

I do love the idea of alerts and planning for future expansion. I am just not sure this would be a sense issue opposed to working with a reputable electrical contractor to review prior to making large additions (adding more breakers - electrical use options) to the panel. Just my $.02

Agree ideally and in an ideal world 80% rule applies. But we aren’t in an ideal world. Also competent electricians who actually know more than what NEC stipulates are hard to find. Most I have spoken to, barely know the difference between residential and commercial CB in terms of sustained load over time. They invariable fall back to 10,000 kA rating! Thus - the need. As for HO - 99% won’t even go near an electrical panel.

The “80% rule” isnt code its the rating of your main… Lets say you have a 200 amp box with 40 slots …breakers are rated at 80% of their values therefore your main breaker of 200amps is rated for 160amps. So if you would reach 160 amps (80%), the main breaker would flip. Obviously you got 40 slots… if you put 20-100amp subpanels/ 20x 100amp breakers (2,000amps) in your panel. And yes, I get that the breakers are rated at 80%. Even if you just have 1 15 amp breaker in each subpanel, you would never flip the main …This rule which is NEC 705.12(D)(2)(3)(c) which says you cant exceed the bus bar (200amps) rating. This one has 2 parts, you cant put a main breaker that the listed rating exceeds the bus bar. Meaning you cant put a 201 amp main breaker in a 200 amp panel. The 2nd part says the sum of the all the ratings of all the overcurrent devices on panelboards, both load and supply devices. So your in a 200 amp panel… They way most did this was the sum of all the breakers (not including the main) can be 200amps . So if you have 100amp, and 50amp… the remaining breakers could only add up to 50 and still meet this part of the code. That would include solar (supply)
I have heard the argument of this rule that you could run 250amps since the ratings is 80%. 250* 0.8=200amps and I agree with that argument unlike some inspectors.

Then the 120% rule is actually NEC 705.12(D)(2)… Says you can add up 120% which using another power source. So if your in a 200 amp box, a 40 amp breaker for PV would be max. The idea there is 160 from your main and 32 from your inverter powering the bus bar at the same time= 192 amps which is below the bus bar rating of 200amps. All of this is design not to have overcurrent any part of your system. I’ve defiantly seen 200 amp boxes that have 350 amps of breakers in them and I didn’t think it was un-safe. However if you have 2 string inverters with 40’s on them each then you can have 160+32+32=224 amps and no breakers flipping though your bus bar is melting.

Why is why I dont fell that its “un-safe.” So if you have 300 amps in breakers going to loads and you have 200 main/ 40 PV… Nothing is going to overload. If your actual load on the breakers exceed 192amps with the PV at max then your main will flip.

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Yeah, I read that. It is a completely useless feature that my cell phone has, you know, the Alarm function, part of the clock. What I want is to get an alert when total usage exceeds a KW setpoint.