EV chargers, Article 220.83, Article 310.12, another residential idiot arguing with the AHJ!

[jaggedben]

Are you saying all A/C loads are continuous? I disagree. Even when running full blast, the operating current will only match the nameplate current under a particular combination of indoor and outdoor temperatures. I don't think it would be "expected" for those conditions to last for over 3 hours.

Cheers, Wayne

You don't? I do. Especially given the heatwaves we are getting nowadays. Plus some people leave their doors open with the air-conditioner running.

 

[ramsy]

What do you mean by part II & III demand factor?

Starting with 220.18(C), and the tables in Part III.

Did not realize demand factors for feeders & services in part IV could be piled on top of demand factors in previous parts.

 

[jaggedben]

By applying the EVSE charger with a demand factor of 40% then you will end up overloading the service in no time. ...

... So 4 chargers is probably the most we are going to get.

4 chargers at full load, running continuously, at the same time, is a full load current of 192A and if you factor in the continuous load, you will be over 200.

Based on the optional method you are okay with 4 chargers and 310.12' reduction to have the lights, chargers, AC units, etc. running and be okay.

Based on good judgement, you are setting them up to trip their breaker or worse.

I mean, not too many dwellings are looking to install four EVSEs, let alone four at 48A, although two is going to be common enough. And the Part IV calcs (not to mention the Part III calcs) are already conservative enough for most dwellings (by a factor of 3 or 4, in my experience) that I bet the vast majority of 200A services would never trip with, say, four 32A EVSEs. Most dwelling unit data I have access to shows the EV load (if there is one) dwarfing all other load.

But I'm not saying your point isn't well taken. As tortuga said, this really needs to be addressed before 2026.

 

[jaggedben]

Clearly the optional calc goess off the rails with EVSE @ 40%, and I could easily have three or more EVSE's at a large home, I think the OP's AHJ made a determination that you can't use any optional calcs with an EVSE. The AHJ does not want to chance it case by case. The 220 optionals need updating and sooner than 2026.

More reasonable than going to Part III would be to do what a couple AHJs I've dealt with have done, and simply require the EV load to be added (at 100%) to the rest of the Part IV calc.

 

[wwhitney]

You don't?

HVAC is a bit outside my expertise, but (a) most A/C systems are grossly oversized, so they won't run full blast for 3 hours even under design worst-case conditions and (b) even if you have a non-oversized A/C unit, and it runs for 3 hours straight during a heat wave, I bet its current draw will still vary over that 3 hours, and (c) even if its current draw is sufficiently constant over those 3 hours, my understanding is that it will typically be below the nameplate current.

The nameplate current corresponds to some idealized set of conditions of indoor and outdoor temperature and relative humidity, which I presume is a theoretical worst case, and real world indoor and outdoor conditions are not likely to match those idealized conditions for 3 hours straight. It is, to my understanding, akin to asking how often a solar panel will put out its full nominal rated power.

Cheers, Wayne

 

[tortuga]

Guys if we want to dust off the do we need to consider continuous loads on a residential service cals debate I say we go back to that thread.
For this OP his inspector calculated a load at 194 amps:

The inspector refuses to approve the permit, because when he performed a standard load calculation, it came out to 194 amps, which is both a large discrepancy from the optional method, and also above the rated ampacity of 4/0 aluminum according to 310.16.

Can we all agree that 4/0 AL can be used to serve this load per 310.12(A)?

 

[Ken_S]

All info below relates to the 2020 NEC
A relatively new inspector in a town that I don't do a lot of work in requested a service load calculation for a new EV charger install I gave a quote for. It is an existing single family dwelling unit, with a 200 amp CHTH main breaker panel fed with 4/0 aluminum SEU, and the customer wants a 48 amp Tesla Wall Connector installed.
I performed a load calculation using article 220.83, and the load came out to 138 amps. The inspector refuses to approve the permit, because when he performed a standard load calculation, it came out to 194 amps, which is both a large discrepancy from the optional method, and also above the rated ampacity of 4/0 aluminum according to 310.16.
I argued that 220.83 is a valid method to determine whether an existing service is capable of handling an increased load, which he argued it was not (and then later backtracked), and also said that 310.12 does not say anything about the calculated load, only the size of the service equipment.
Am I crazy? Am I interpreting article 310.12 incorrectly? Is the AHJ allowed to pick and choose which load calculation method is acceptable or not? He wants me to install 250kcmil aluminum service entrance conductors (based on his unprompted load calculation) before he will approve my permit. Let me know what you guys think.

Reach out to code assistance, they generally respond quickly

 

[jaggedben]

HVAC is a bit outside my expertise, but (a) most A/C systems are grossly oversized, so they won't run full blast for 3 hours even under design worst-case conditions and (b) even if you have a non-oversized A/C unit, and it runs for 3 hours straight during a heat wave, I bet its current draw will still vary over that 3 hours, and (c) even if its current draw is sufficiently constant over those 3 hours, my understanding is that it will typically be below the nameplate current.

The nameplate current corresponds to some idealized set of conditions of indoor and outdoor temperature and relative humidity, which I presume is a theoretical worst case, and real world indoor and outdoor conditions are not likely to match those idealized conditions for 3 hours straight. It is, to my understanding, akin to asking how often a solar panel will put out its full nominal rated power.

Cheers, Wayne

Okay, it's rather outside of my expertise, too, but my understanding is the vast majority of compressors out there are still old-style single speed. So when they are on they draw the rated amps or pretty close to it. I guess I don't know as much about the variability of the indoor unit loads. My impression is that simple window units also just go at the rated amps, more or less, and I think lots of people leave those on for 3 hours, or set the thermostat so low that it happens. It seems to me an unwarranted assumption that an AC unit will never run at full load for 3 hours.

 

[wwhitney]

For this OP his inspector calculated a load at 194 amps:

Well, this is the inspector's first error, requiring the use of Part III. The applicant has the option to use Part IV. So the load is 138A, per the OP.

Can we all agree that 4/0 AL can be used to serve this load per 310.12(A)?

I agree that is the common interpretation. I'm less convinced that the language in 310.12 is actually crafted in a way that overrides other sections that refer to a feeder's or service's ampacity without using the phrase "service rating." Which phrase is unique to 310.12 (at least according to a search of the 2017 NEC, the last version I have as a text PDF) and the examples in Annex D.

Cheers, Wayne

 

[jaggedben]

...
For this OP his inspector calculated a load at 194 amps:

Can we all agree that 4/0 AL can be used to serve this load per 310.12(A)?

I wish. See the thread that I cited at the beginning of this one. The OPs inspector being apparently already convinced otherwise, then if Wayne does not see a slam dunk logical argument, one may be SOL.

See my post #56 in that same thread. It wasn't supposed to be that way, and doesn't need to be, but that's where we are.

 

[wwhitney]

Okay, it's rather outside of my expertise, too, but my understanding is the vast majority of compressors out there are still old-style single speed. So when they are on they draw the rated amps or pretty close to it.

A single speed unit will run its compressor at a fixed speed when on, but the current draw from that compressor will vary according to the indoor and outdoor temperatures and humidities. Just like any motor's current draw will depend on the mechanical load on that motor.

It seems to me an unwarranted assumption that an AC unit will never run at full load for 3 hours.

I'm saying that I would generally not expect it to happen in practice, not that it's not possible.

Cheers, Wayne

 

[tortuga]

Can we all agree that 4/0 AL can be used to serve this load per 310.12(A)?

I wish. See the thread that I cited at the beginning of this one. The OPs inspector being apparently already convinced otherwise, then if Wayne does not see a slam dunk logical argument, one may be SOL.

See my post #56 in that same thread. It wasn't supposed to be that way, and doesn't need to be, but that's where we are.

#56 that was a great comment I am going to use that in a class. The OP appears to be on the 2020 but yeah 2023 NEC 240.4(H) clearly says " Dwelling unit service and feeder conductors shall be permitted to be protected against overcurrent at the ampacity values in 310.12"
And 310.12 says 4/0 AL is 180A/.83 = ~217 amps or a 200A service rating. 194 < 200

 

[tortuga]

Here is where 310.12 came from, it started in the 1956 code to promote aluminum wire and was unchanged until the 1971 when the copper lobby caught on and wanted copper added also:

310.12 allows Dwelling unit service and feeder conductors to carry a larger load and thus be protected against overcurrent at a higher ampacity listed in 310.12, due to the reduced 2 CC's.

 

[KevinKos]

Your situation involves two key areas of the 2020 NEC: the use of the optional method for load calculation and the interpretation of conductor sizing requirements. Here’s an in-depth look at the relevant sections and the arguments you can use to support your position.

Article 220.83 - Optional Method for Existing Dwelling Units​

NEC 220.83 allows for an optional method to determine the load for existing dwelling units. This method can be used to evaluate if the existing electrical service is adequate when adding new loads, such as an EV charger.

Key Points from NEC 220.83:

1. Applicability: This section applies specifically to existing dwelling units where additions or modifications are made.
2. Load Calculation: The optional method considers the existing loads and uses demand factors to calculate the total load. This often results in a lower calculated load compared to the standard method.

Based on your calculation using 220.83, the total load came to 138 amps, which is within the capacity of a 200-amp service with 4/0 aluminum conductors.

Article 310.12 - Service Conductors for Dwelling Units​

NEC 310.12 addresses the minimum size of service conductors for dwelling units.

Key Points from NEC 310.12:

1. Conductor Sizing: For single-family dwellings, service conductors must have an ampacity of not less than the calculated load and meet the requirements of Table 310.12.
2. 4/0 Aluminum: According to Table 310.12, 4/0 aluminum conductors are rated for 180 amps when used for 100% of the load. This can be extended to 200 amps under certain conditions, specifically for residential services.

Article 310.16 - Ampacity of Conductors​

NEC 310.16 provides ampacity tables for conductors.

Key Points from NEC 310.16:

1. Ampacity of 4/0 Aluminum: Under standard conditions, 4/0 aluminum SE conductors have an ampacity of 180 amps. However, the 310.12 table can allow for higher ampacity in certain residential applications.

Authority Having Jurisdiction (AHJ)​

NEC 90.4 grants the AHJ the authority to interpret and enforce the NEC.

Key Points:

1. Interpretation Authority: The AHJ has the authority to interpret the code and ensure its enforcement, but they should provide a valid reason if they choose to not accept a recognized calculation method.
2. Optional Methods: The NEC allows for optional methods of calculation (like 220.83) and these should be acceptable as long as they are applied correctly.

Addressing the Discrepancy​

1. Valid Use of 220.83: Clearly explain that 220.83 is specifically designed for situations like this. It takes into account the diversity of loads in a dwelling and provides a realistic load calculation.
2. 310.12 and Service Conductor Sizing: Highlight that 310.12 allows 4/0 aluminum conductors to be used for services up to 200 amps in residential applications. This is consistent with your load calculation of 138 amps.
3. AHJ's Calculation: If the AHJ's calculation using the standard method results in a load of 194 amps, request a review of the assumptions and demand factors used. Differences in methodology or incorrect assumptions about load diversity could explain the discrepancy.

Your Action Plan​

1. Documentation: Provide the detailed load calculation using 220.83, showing all steps and demand factors used.
2. Clarification: Request the AHJ to provide a written explanation for their interpretation, specifically why they are not accepting 220.83.
3. Resolution: If the AHJ insists on using the standard method, request a meeting to discuss the differences in the calculations and see if a compromise or further clarification from a senior inspector can be obtained.

 

[nizak]

Just out of curiosity, has anyone got a 1 year peak usage from the Utility ?

I recently went to 4K square ft residence with a host of high wattage goodies ( hot tub, clothes dryer, range , wall oven, outbuilding,garage unit heater, pool pump, etc) and found a peak load of 17.3 KW on the smart meter coding.

A load calc by the book would have easily shown double that number.

 

[jaggedben]

Just out of curiosity, has anyone got a 1 year peak usage from the Utility ?

I recently went to 4K square ft residence with a host of high wattage goodies ( hot tub, clothes dryer, range , wall oven, outbuilding,garage unit heater, pool pump, etc) and found a peak load of 17.3 KW on the smart meter coding.

A load calc by the book would have easily shown double that number.

Was 17.3kW for an hour interval? Or 15 min? Or...??? If it's one hour, you gotta be kinda conservative as that usage could have been concentrated in a smaller time period.

Still, you are correct that many houses never use more than 100A, in fact many don't even get close. I can see 15 minute data for all of my clients and have never seen more than 20kW. Not that we work in a high air-conditioning area, but still, most usage is well under that. Pretty much only people with EVs ever get over 10kW, even in all electric homes. The code calcs are usually quite conservative.

 

[Birken Vogt]

I'm not sure what section you're referring to, but I'm pretty sure I disagree. Many people charge their EVs at any time of day, whether or not they should.

This was in regards to your question, what code section allows load management to keep under the total load rating of conductors or whatever.

It would be unlikely for the loads to operate simultaneously if the load management system is actively working to prevent that.

 

[Birken Vogt]

Okay, it's rather outside of my expertise, too, but my understanding is the vast majority of compressors out there are still old-style single speed. So when they are on they draw the rated amps or pretty close to it. I guess I don't know as much about the variability of the indoor unit loads. My impression is that simple window units also just go at the rated amps, more or less, and I think lots of people leave those on for 3 hours, or set the thermostat so low that it happens. It seems to me an unwarranted assumption that an AC unit will never run at full load for 3 hours.

Air conditioners seldom draw rated amps, even when running continuously. If inside temp or outside temp drop, amps go down.

We are having a heat wave soon. Go measure yours and report what it does.

 

[jaggedben]

Air conditioners seldom draw rated amps, even when running continuously. If inside temp or outside temp drop, amps go down.

We are having a heat wave soon. Go measure yours and report what it does.

Mine is variable speed and we probably won't use it.

I guess I've been extrapolating from a quite small number of single speed compressors that I've amp clamped on clients houses. But also don't MCA specs contain a 125% factor? And 440.31? What are those for?

 

[Birken Vogt]

On any standard AC unit, it will display the compressor amps, fan amps, and MCA.

The MCA is always (compressor amps) + (compressor amps x 0.25) + (fan amps)

So yes, it contains the "largest motor" already built in.