Checking panel for capacity to add EVSE circuit

R

Robert_Alabama

Well-Known Member
The last posts on this got way off the general topic of the thread, so I thought I'd start a new thread. Hopefully I can do a better job of at least introducing the topic and having some constructive discussion. If I fail again, I'll probably just give up, but I tried... and for what it is worth, I am trying to be helpful.
I'll give a specific example of a panel in my house:

I have a panel that has a 200A main breaker, three 240V breakers, and 16 120V breakers. The sum of amperage of the 240V breakers is 130A and the sum of the amperage of the 16 120V breakers is 265A.

From what I understand for NEC here, there are 3 accepted methods to show the panel loading doesn't exceed the 200A capability.
1) add all amperages of the breakers (assume 120V load is balanced). This would be 130A plus 0.5*265A = 262.5A. So this method will not work to show the panel is not overloaded.
2) put a ammeter on each of the two hot legs feeding the panel and record amps at 15 min intervals for 1 year (or a minimum of one month in the peak load season) - this is not practical for most of us to do, and I'd probably only do it as a last resort. With this method, you would take the highest amp reading and multiply by 1.25 to get the panel loading.
3) add up all the loads on each of the circuits and multiply by 1.25 for a continuous rating. For this panel:
240V breaker #1 (30A) Dryer - 5400W or 22.5A
240V breaker #2 (60A) 5T A/C - 26.3 RLA for compressor and .97 FLA for fan - total 27.3 A
240V breaker #3 (40A) 4T A/C - 18.5 RLA for compressor and .93 FLA for fan - total 19.5 A
120V breaker #1 (20A) Refrigerator - 3.3A from nameplate
120V breaker #2 (20A) Washing Machine - 10A from nameplate
120V breaker #3 (20A) Kitchen island outlets - Hardly ever used - approximate as 3A
120V breaker #4 (20A) Utility room plugs - never used - approximate as 2 A
120V breaker #5 (15A) Attic squirrel cage motor for A/C air handler - 6A
120V breaker #6 (15A) Guest bedroom lights - LED lights - 1A
120V breaker #7 (15A) Guest bathroom lights and plugs - 12A (assume small hair dryer)
120V breaker #8 (15A) Child bedroom lights - LED - 1A
120V breaker #9 (15A) Bonus room - not used - LED lights 1A
120V breaker #10 (15A) Garage lights and plugs- LED lights - 12A (just in case 120V evse is plugged in)
120V breaker #11 (15A) Foyer lights and plugs - LED lights -1A
120V breaker #12 (15A) Child bedroom lights - LED lights - 1A
120V breaker #13 (15A) Office lights and plugs - computer and printer - LED lights - 5A
120V breaker #14 (15A) Attic lights - LED lights 1A
120V breaker #15 (15A) Playroom - no TV or media- LED lights - 1A
120V breaker #16 (20A) Porch fans - LED lights - 2A

This sums to 69.3 A on the 240V breakers and 62.3A at 120V (31.15A at 240 if balanced)
This total is 69.3A + 31.15A = 100.45 possible continuous load
add 25% for continuous load rating of panel = 100.45A *1.25 = 125.56A

If I wanted to add a 60A circuit in this panel, I would pretty much just have enough room as 125.56A + 60A = 185.56A. I made a lot of approximations on the 120V circuits and assumed perfectly balanced load which is likely not right, especially since all these circuits were planned with incandescent lighting load when they were attempted to be balanced, so I would feel better leaving a few amps to spare in the calculation. If I messed any of this up, I apologize as again, I am not a licensed electrician. I simply wanted to state that there is a process for determining panel loading which generally assumes all connected load is simultaneously on (with the exception of heaters and A/C - take the larger of these loads). It is not acceptable to add a circuit and say that I won't charge the car when the range/dryer/air conditioner is on and that as such the panel loading is ok. Again, if I am off base on this, I apologize in advance and I'll accept any criticism thrown my way...
 
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The reason the other thread went south is because you attributed a statement to me that I did not make. Despite efforts to clarify and explain to you exactly what I said, you refused to understand or recognize what you had done. Instead you spun the discussion into one about methods to determine panel loading rather than acknowledging my concern about being misquoted. I hope you find that to be constructive criticism.
 
I do not have the patience to read through the NEC, but since the standard panel is designed for more breakers than can reasonably hold under its stated capacity, I do not believe there is any such rule.
In industrial settings perhaps
Putting a meter on a circuit is random.
Is my well pump running?
Is my oven running?

Current code encourages many 120 volt circuits that were not used many years ago resulting in phantom 'load' by counting breakers
 
You are right there is no rule that the sum of the breaker ratings has to be less than the capacity of the main. This was a conclusion that maybe my discussion led to, but not what I was trying to imply.

I never said that it meant that the load likely exceeded the rating of the main breaker. I said that this method generally fails (or likely fails) to prove that the load does not exceed the rating of the main breaker. There is a big difference in these two statements. As such, this method probably rarely is helpful in proving the panel isn't overloaded, but nonetheless it is one of the methods for showing the panel isn't overloaded (if it happens to pass). Again, if it does fail to prove the panel isn't overloaded, it doesn't imply that the panel is overloaded, just doesn't qualify as proof that it isn't.

As to the meter on the panel as a method, you are also right and I am not particularly fond of this method, but I think the random nature of the load is why this requires at least a month of continuous recording (with references to one year) and at 15 minute intervals. The belief is that over this time all connected loads that might be simutaneously on would show up in the recorded data at least once and set the highest reading.
 
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Robert_Alabama said:
2) put a ammeter on each of the two hot legs feeding the panel and record amps at 15 min intervals for 1 year (or a minimum of one month in the peak load season)
Click to expand...

This is probably the 'best' way, and it may not be as impractical as it sounds. There are a several ways you could approach this.

1. for anyone who is highly tech-savvy, it is possible to continuously record whole house energy usage on an instantaneous and continuous basis by instrumenting the optical port on your smart meter. Chances are that your meter looks something like this:
upload_2025-3-5_8-1-0.webp
The meter produces optical pulses which you can detect with a photodetector. With a simple microcomputer you can count these pulses for real-time measurement of your whole-house consumption (amperage). I have done this, but obviously this is not practical for everyone. I can provide great detail to anyone who is specifically interested.

2. For those who are not as technical, there are reasonably priced systems available that can be installed by an avid DIY person (or an electrician). Here is an example of one of the more popular ones. This one does your whole house AND up to 16 branch circuits (and costs $200):
https://a.co/d/dUOirE8

Or, If you just want to just do the whole house, then there is a lower cost one ($100):
https://a.co/d/92gercB

3. For almost anyone else - it is quite possible that your electric company already provides you with the information that you need. In Maryland (it is Constellation Energy). You can log into your account and view your electric usage. You can see usage on a yearly, monthly, or daily basis. When you view the daily usage, it provides an hourly measurement (yes, this is an hourly interval, not the 15 minute interval that Robert cited), but it is pretty darned good and likely would be perfectly fine for this purpose. In my case, it is easy to scroll through day by day and find the peaks over an extended period. Here is an example for my house from a few days ago...

upload_2025-3-5_8-12-2.webp

Note that on this day, the peak usage was nearly 6 kWh, so that is 6 kW for the 1 hour period which equates to 25 Amperes at 240 Volts.
 
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@MrFixit , thank you for the input and great to know this isn't all that invasive or painful. My home does complicate it a little as I have split panels, so I couldn't use info from the utility or the meter. I'd have to connect to the panel that I would be looking into, so I would need option 2 (either the $100 or $200 package). Still, thank you for the insight and the link to the resources, good to know.
 
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Robert_Alabama said:
My home does complicate it a little as I have split panels, so I couldn't use info from the utility or the meter.
Click to expand...

Don't rule out out the utility information !
Think about it this way - If the grand total (sum of both panels) is OK, then either one of them is also OK. It is quite possible that you are well under the limits and a whole house measurement could demonstrate that. If the whole house exceeds the desired limit, then you would have to look at each panel individually.
 
Robert_Alabama said:
I'd have to connect to the panel that I would be looking into, so I would need option 2 (either the $100 or $200 package).
Click to expand...
Another potential option for you that is even easier and cheaper ($39) to implement is the Emporia Vue - Utility Connect device. To use it, you need to have an eligible utility provider and smart meter. If so, you don't even have to attach anything inside your service panel - the device connects to your home's wifi and then connects wirelessly to your smart meter (after you call the utility company to request that connection). I've been using mine since last April with no issues. With it, I can track the watts used/generated by my entire home (I have rooftop solar) by the minute, hour, week, month, and year. The data are collected straight from your meter so it is 100% accurate.
 
@NorCalPete
I was not aware of this, and it seems like a great option !!!

But - on the page you sent, it looks pretty limited as to where this is currently available:
--------------------------------------------------------
upload_2025-3-5_14-5-17.webp
------------------------------------------------------------

Unfortunately it does not cover my area... Once you purchase the device, I assume there are no ongoing subscription fees from wither Emporia or your utility company?
 
@MrFixit, you are correct on both counts: limited applicability but no subscription or connection fees. I suspect that the limited application is why the device isn't widely marketed/advertised.

My home has a complicated setup where the original undersized 100 amp service panel was converted (via a "Hawaiian Tie-in") into a 200 amp service panel. This allowed me to double the size of my net-metered solar array without the additional cost (approx $10k) of installing a larger service-line/service-panel to my house. The Hawaiian Tie-in cost about $500, follows NEC rules, and passed all inspections. Unfortunately, it also limited my options for monitoring all of my home's power usage. After a lot of online searching, I stumbled upon the Vue Utility Connect that bypassed all of my service panels and subpanels and, instead, pulls the data directly from my utility meter.
 
Robert_Alabama said:
You are right there is no rule that the sum of the breaker ratings has to be less than the capacity of the main. This was a conclusion that maybe my discussion led to, but not what I was trying to imply.

I never said that it meant that the load likely exceeded the rating of the main breaker. I said that this method generally fails (or likely fails) to prove that the load does not exceed the rating of the main breaker. There is a big difference in these two statements. As such, this method probably rarely is helpful in proving the panel isn't overloaded, but nonetheless it is one of the methods for showing the panel isn't overloaded (if it happens to pass). Again, if it does fail to prove the panel isn't overloaded, it doesn't imply that the panel is overloaded, just doesn't qualify as proof that it isn't.

As to the meter on the panel as a method, you are also right and I am not particularly fond of this method, but I think the random nature of the load is why this requires at least a month of continuous recording (with references to one year) and at 15 minute intervals. The belief is that over this time all connected loads that might be simutaneously on would show up in the recorded data at least once and set the highest reading.
Click to expand...
I'm sorry
It requires none of this
It requires 100 years of history of panels not burning up, which we already have

I do not understand your point or motivation
 
ENirogus said:
I'm sorry
It requires none of this
It requires 100 years of history of panels not burning up, which we already have
I do not understand your point or motivation
Click to expand...

Earlier, you said this ---

ENirogus said:
I do not have the patience to read through the NEC
Click to expand...

If you aren't going to read the NEC, then your comments here are not really relevant.
This has nothing to do with 100 years of history, or not burning up panels. The breakers will always prevent 'burning up'

EV's are 'new' in the scheme of things, and they represent the single largest load you will have in your house.
What is relevant here is whether your house / panel can support adding an EVSE with a very low probability of nuisance tripping of your main breaker. The only way to know this is by evaluating your current demand, and because indeed, the demand varies greatly from hour to hour, day to day, this requires some sort of detailed monitoring in order to catch the peak load conditions.

The motivation here is clear... You don't want to go through the effort and expense of installing a very high load without some quantitative evidence that you are not going to be tripping a breaker every time you charge your vehicle !
 
I’d recommend most home owners use Option 4. Call an electrician. Benefits include a free estimate and less time wasted, since a professional will be able to tell you what’s possible within 10-15 minutes. Chances are you aren’t going to do the work yourself anyway, because if you knew what you were doing you wouldn’t be wasting time trying to figure it out.
 
Landshark said:
I’d recommend most home owners use Option 4. Call an electrician. Benefits include a free estimate and less time wasted, since a professional will be able to tell you what’s possible within 10-15 minutes. Chances are you aren’t going to do the work yourself anyway, because if you knew what you were doing you wouldn’t be wasting time trying to figure it out.
Click to expand...

Indeed. Why would one ever choose to attempt to educate oneself, when you can always just get someone that you should inherently trust to tell you what you need to do? This is wise advice for life in general. I'm going to have to rethink my life (and most of my parenting advice and examples I have tried to give my children) over the years. Sad you are often enlightened on these life altering insights when it is just too late and after you have wasted much too much of your life and especially after you have attempted to engrain such behavior into your descendants. I'll just have to live with that and take it to my grave, I guess. I wish i could be thankful for this new insight, but it just makes me remorseful that I have learned this lesson much too late. Guess I will just have to work to learn to live with it. Maybe I can use trying to adjust myself to this new philosophy to fill the vast amount of time I will now have available.
 
Robert_Alabama said:
Indeed.
Click to expand...

Great to hear from you. Now that we’re back on speaking terms, what are your thoughts on misrepresenting my statements on the other thread?

We can discuss your personal issues later, if you’d like, although I’d recommend seeking the advice of a professional rather than attempting to work through it on your own.
 
MrFixit said:
Earlier, you said this ---



If you aren't going to read the NEC, then your comments here are not really relevant.
This has nothing to do with 100 years of history, or not burning up panels. The breakers will always prevent 'burning up'

EV's are 'new' in the scheme of things, and they represent the single largest load you will have in your house.
What is relevant here is whether your house / panel can support adding an EVSE with a very low probability of nuisance tripping of your main breaker. The only way to know this is by evaluating your current demand, and because indeed, the demand varies greatly from hour to hour, day to day, this requires some sort of detailed monitoring in order to catch the peak load conditions.

The motivation here is clear... You don't want to go through the effort and expense of installing a very high load without some quantitative evidence that you are not going to be tripping a breaker every time you charge your vehicle !
Click to expand...

There is no reason that an EV should be the single highest load, although it can be. I have run a 240v 20 amp evse for coming on 4 years
Since you are not offering any real technical advice, I do not see the point of your post.
If you have a 200 amp or greater panel, it seems unlikely you will blow your main breaker.
Is there a spate of reports of main breakers popping?
I think not.
Why?

Because all of the loads in your house must be wired for peak load, not average load
They never, ever peak load simultaneously
Cannot remember the last time I had all 5 elements on my range on high, while drying the laundry, the dishwasher on dry cycle, the computer mining crypto, every light in the house on, the table saw making a deep cut in oak, 3 TVs playing DVDs with the sound on full blast, watering the lawn full blast so the well pump is running non stop................
yet............
each one of those circuits is wired so that it can handle its peak load, but as I pointed out, it is impossible to run all these things at the same time

So stop it
FUD pure and simple.

If you have a small, old panel, it may need to be upgraded
If you have no reason to have a large EVSE, do not install one
 
Landshark said:
Great to hear from you. Now that we’re back on speaking terms, what are your thoughts on misrepresenting my statements on the other thread?
Click to expand...
I doubt that any thoughts or perspectives I might have are of little real value to you. My recommendation would be to seek the advice of a professional to see what they thought. That position is really growing on me.
 
Robert_Alabama said:
My recommendation would be to seek the advice of a professional to see what they thought.
Click to expand...

I’ve given it some thought and concluded that if someone is unable to understand clearly worded statements in addition to further clarification of those statements, they probably aren’t going to be capable of understanding the NEC Code.

I have no objection to gaining literacy on a subject, as you have incorrectly assumed. My point is that a person of moderate intellect will be able learn everything they need to know about adding a circuit to their service panel during a 10 minute conversation with a licensed electrician. So, rather than spending time digesting the NEC Code and more time ruminating about it on internet forums, just pick up the phone and call a professional.

FWIW: My 40 year career involved installing and working with temporary power installations. Not as a licensed electrician but as a qualified union member, specifically trained and educated to work in the field. I can’t recite the NEC Code, but I would likely be able to tell someone whether or not they have the capacity to install a circuit for a L2 EVSE. Then I’d advise them to call an electrician.
 
I said that there were 3 methods, if any of the methods pass, it indicates that the panel is not overloaded. If any of the methods fail, it doesn't mean that the panel is overloaded, just that the individual method doesn't prove it isn't. One of the three methods is summing up the ratings on the breakers and comparing that to the rating of the main. So the test is whether the sum is greater than the main breaker rating. If it is greater, it doesn't mean that the panel is overloaded, only that the test fails (and of course that the sum exceeds the numerical value of the rating of the main).
 
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