Mike Dolt Enterprises
Mike Dolt Enterprises
User: Josuea1990, Location: Florida, USA
Asked on: Sunday, July 20, 2025 at 7:55 pm EDT
Answered on: Sunday, July 20, 2025 at 7:55 pm EDT
Question: Greetings!Whole house generator with ATS question:So, it seems to me that in every YouTube video I've watched about standby generator installs with whole house automatic transfer switch on houses that have a 200 A service, and in other, even a farm with A 400 A service with two 200 A panels being fed by a 24 kw generator, they are all just not following 702.4 (b)(2)(a), and they even show that they passed inspection and even had utility come disconnect and all that jazz. I keep scratching my head on ¿how are they passing inspections? Since they all talk very loosely on how to size it. Never mention anything about load calculations in article 220 since the whole house is being automatic transfered, and they just speak about what appliances they would like to run during a power outage as if these appliances were all electric (because if they were not, then why would they be so worry to be able to run them with generator power) things like a/c, cooking, heating and lights and internet they loosely mention for houses that i can clearly see are douple or triple the sq.ft. of my Apt. which i used to compare. They are esentially sizing it based on personal preference.For example: I live in a 1080 sq.ft. Apt. all electric, and I performed an optional load calc. to see what size Gen. would i be requiered, if I were to install whole house auto. transfer Well, result was 22kw (22kw÷240= 91.66 A) minimum and it makes sense because I have a 100 amp main. At one point somebody applied this same calc. on my dwelling unit in the past and decided to install 100 amp main. And on this videos I've watched they are picking arbitrarily numbers for all electric house (it seems), and clearly double or triple the sq.ft. of my home. For example, on the video with the farm guy he don't have natural gas, so he had propane installed for his 24 kw Gen. feeding two 200 A panels (meaning he never had gas, so he is all electric) and he passed inspection.They all pick 24, 22, 20,18, even 14 kw units.Just the other day here in florida, even my boss told me on the phone (after I went rushing stretching my 100 ft tape measure around an all electric costumer's house to figure out the total 1968 sq.ft. and took pictures of all nameplates, then sit in the van to make an optional calc. and come up with a 28kw which we don't even carry, since the max we carry is 26kw, to give an estimate (all in 30 min). He says: "well, that 200 A house will do well with a 22 kw. And after the scared reaction for the 22kw price of the costumer who was expecting us to auto transfer the whole house, my boss asked me to say that we can do it cheaper and install an 18kw and they'll be fine (even my boss is picking arbitrarily numbers to make the sale, knowing the costumer wants permit to be pulled, inspection and all that jazz).How can you explain this videos with inspections passed? Then I tought: "well, maybe they are using 220.87 to come up with a lower number, although they never mention that". But even if they were, how do you explain the Florida videos when even my self went ahead to make sure if we floridians have acces to the maximum demand data history over a one year period from the utility Co. like in some other states. So i called them and asked them for a one year period data on an excell format, so then i could use the max tool on excell to find the highest 15 min or 30 min (however often your utility captures) interval kwh meter registration to then in turn convert that in to kw. Well, at least here in florida that format is not available, all they have is kwh by the hour (hourly insterval registrations) for every day of every month and you have to find it yourself by logging into your account in their website on your energy usage dashboard and by manually looking day by day through the 12 months history for the highest kwh registration wich becomes the same as your highest kw demand per hour, this is insanely time consuming for when you are trying to use this method to calculate for a costumer that's interested on a whole house automatic transfer to come up with the lowest (cheaper) gen. size requiered by code per 702.4 (b)(2)(a) and using 220.87 to comply with the calculation part because the actual historical demand will always give you the lowest number and you could beat the competition and make the sale.Now between you and me, we know an average 200 A house withouth an EV charger does not see more than 75 amps on a regular basis, and 75x240= 18kw, so in reality, yeah! 18 kw (don't worry about starting currents on A/C generac is rated to withstand them) will do the costumers house based on real history usage peak demand per 220.87, but if i can't get that paperwork from the utility, how can i prove it to the inspector?.Now, what is going on with me? I'm I the only one worrying to comply with 702.4 (b)(2)(a) ? What if the inspector fail us for not sizing the generator properly, after purchasing materials and generator and start doing the job and all that jazz? Is it that inspectors don't really care because there is no safety hazard involved in it? I mean the worst thing that can happen is that the generator it self won't hold and trip it's own breaker right? or fail due to overloading or simply reduced its lifespan, which ultimately the only affected one will be the costumer, who'll end up with no power and a broken generator. Maybe that is why they are not requiring 702.4 (b)(2)(a) to be followed? What do you think ? I mean, at the end of the day is an "OPTIONAL" standby system.
You've hit upon a really frustrating and common issue in the electrical trade: the gap between code requirements, practical application, and what actually gets enforced. You're absolutely correct in your analysis of 702.4(B)(2)(a) and the load calculation requirements of Article 220.Let's break down the points you raised and explore potential reasons for the discrepancies
1. Code Compliance vs. Reality:
You're Right on the Code
The NEC clearly states the generator must be sized to carry the calculated load determined by Article 220. That means a proper load calculation using the methods specified.
Optional Calculation Complications
The optional calculation can lead to a much higher generator size, especially in all-electric homes. This is exactly what you're seeing with your 22kW calculation for your apartment and the 28kW for the customer's house.
The Disconnect
The disconnect comes from how often people actually use all their appliances simultaneously at their peak demand. The NEC calculations often represent a "worst-case" scenario that rarely happens.
2. Why the Discrepancy in Videos and Inspections?
Here are the likely contributing factors: Oversimplification for YouTube
YouTube videos often prioritize simplicity and appeal over strict adherence to code. A detailed load calculation might bore the audience. The focus is on getting some power back during an outage.
Inspectors' Discretion
Electrical inspectors have a degree of discretion. Some might prioritize safety over meticulous load calculation compliance, especially on optional standby systems. They might focus more on proper wiring, grounding, and transfer switch installation than the generator's exact load capacity. If the system is installed safely, they may be more lenient.
Lack of Enforcement
Overload of optional standby system will usually only affect the homeowner, and if the system is installed safely that usually gets a pass.
Local Amendments
Some jurisdictions might have local amendments that modify or relax the NEC requirements for optional standby generators. However, they are not very common.
Trust and Expertise
Inspectors may rely on the installer's professional judgment, especially if the installer is experienced and reputable. They might assume a reasonable level of oversizing.
"It Works" Mentality
If the generator powers essential circuits and avoids nuisance tripping of the generator breaker, inspectors are less likely to dig deeper.
Demand Limiting Technology
Some newer generators and transfer switches have built-in load management systems that can shed non-essential loads if the generator approaches its capacity. Inspectors might be aware of this and less concerned about the initial load calculation.
3. The 220.87 Option and Utility Data
220.87 is a Valid Approach
Using actual historical demand data is the most accurate way to size a generator. It reflects real-world usage, not a theoretical maximum.
Florida's Data Challenges
You're right, the lack of easily accessible historical data from Florida utilities makes it difficult to use 220.87 effectively. Manually scouring hourly data is incredibly time-consuming.
Justification Without Data
Without the data from the utility, it's harder to convince an inspector that a smaller generator is adequate based on code. You'd need a compelling argument based on the homeowner's usage patterns and appliance specifications.
4. Your Boss's Approach (and the Ethics of It)
Sales Pressure
Your boss's approach is driven by sales pressure and the desire to make a deal. It's understandable from a business perspective, but it raises ethical concerns.
Potential Liability
Installing a generator that's undersized based on a proper load calculation could expose your company to liability if the homeowner experiences problems.
Informed Consent
At a minimum, the customer should be fully informed about the potential limitations of a smaller generator and the fact that it might not be able to power everything during an outage. It should be in writing.
5. What to Do?
Here's a suggested approach: Know the Code
You're already doing this. Understand the requirements of 702.4(B)(2)(a) and Article 220.
Perform Accurate Load Calculations
Do the optional load calculation, but also try to get as much information as possible about the homeowner's actual usage patterns.
Communicate with the Inspector
Before starting the job, talk to the local electrical inspector. Explain your situation, your concerns, and your proposed generator size. Get their input on how they want to see the calculation justified. This can save you a lot of headaches later.
Document Everything
Keep detailed records of your load calculations, conversations with the inspector, and any agreements you reach.
Involve the Homeowner
Have an open and honest conversation with the homeowner about the generator size and its limitations. Explain the benefits of a larger generator versus the cost savings of a smaller one. Get their informed consent in writing.
Consider Load Management
If a smaller generator is desired, explore using a transfer switch with load management capabilities. This will allow you to prioritize essential circuits and shed non-essential loads if necessary.*
Stand Your Ground
If you believe a generator size is unsafe or doesn't meet code, be prepared to stand your ground. It's better to lose a sale than to compromise your ethics and potentially face liability.
In conclusion: You're not crazy! You're applying the code correctly. The lax enforcement you're observing is likely due to a combination of factors: practical considerations, inspector discretion, and a focus on safety over strict load calculation compliance.Your best approach is to be well-informed, transparent, and proactive in communicating with both the inspector and the homeowner. Ultimately, your goal is to provide a safe, reliable, and code-compliant system that meets the customer's needs. Good luck! Flag for review