220.87 Determining Existing Loads

[JohnHess]

I believe that the residential load calculations we perform are very bloated. Sometimes they can limit what we can install for the homeowner or cause them to spend unnecessary money on service upgrades or load management products. Instead of submitting load calculations with my electrical permit applications I would like to submit 1 year of the actual maximum demand data because I know that will be much lower and more accurate than the load calc.

My question is what the "maximum demand" is, exactly. Our area is served by a very large PoCo and is mostly smart meters now, so I assume that data will be available thru their website. But I am not sure exactly what form it needs to be in to tell me the average load in place of the VA number I get when doing a load calculation.

 

[brycenesbitt]

@JohnHess
Which large PoCo ?

There's a ton of data on this exact issue taken from thousands of homes. And in fact, that data was presented to the NEC committee at the technical meeting stage, resulting in new calc language in the 2026 code cycle.

TL;DR panels have been oversized by those calculations for a long time.

Most of the new formulas made it through the whole cycle, except for one, and that's the subject of an appeal August 18th 2025.
Send a private message I can get you a full summary.

---
For maximum demand it depends on the PoCo. Identify yours for more help. Generally, you can find it on a bill as a "demand charge" or "peak charge". In some cases, you can download 1- or 15-minute data and find the peaks yourself. However, in other cases you only get 1 hour data which is kind of chancy for making load assumptions.

There are now a TON of ways to "peak shave" these days. Or, to have a new device dance about and use power only when the panel has capacity.

------
Eaton's appeal on load related issues reads in part

NFPA Standards Council
1 Batterymarch Park
Quincy, MA 02169

RE: Appeal regarding CAM 70-87 18 July 2025

Dear Ms. Bellis,

I am writing to formally appeal the outcome of certified amending motion 70–87. This is a unique case of where the process created a situation that negatively impacts all parties involved and arguably negatively impacts electrical safety as well. ....
The issue stems from a correlation problem created by the recent process involving Certified Amending Motion 70–87. As per the motion made at the annual meeting, Public Comment 1854 was accepted, which proposed increasing the VA/ft2 for calculating the number of branch circuits in a dwelling unit from 3 VA/ft2 to 4 VA/ft2. ....
If we are not careful, the calculation for the number of branch circuits for a dwelling unit could shift to a 2 VA/ft2 basis....

This motion passed at the annual meeting, and according to NFPA's regulations, such a motion requires that the committee, in
this case CMP-2, be balloted. However, CMP- 2 did not support the ballot. As per the NFPA standards development procedures, when this occurs, the text must revert to the language of the previous edition, which in this case is the 2023 National Electrical Code (NEC). The
2023 NEC did not contain Section 120.13, and NFPA regulations dictate that if no corresponding text exists in the previous edition, the section must be deleted. Thus, Section 120.13 is being deleted.

 

[JohnHess]

@brycenesbitt Thank you for the reply!

The power company is PSE&G in northern NJ.

After doing some searching, I found that PSE&G's commercial bills list the maximum demand right in the sidebar of each bill. However, the residential bills do not. I was not able to find any information like this on my own bill.

PSE&G's website has a lot of data available in multiple forms. My concern is to find the exact type of data necessary and put it together into a way that municipal inspectors will have to accept in lieu of a typical load calculation.

These inspectors are accustomed to saying that a 100A dwelling service can't handle a 48A EVSE. And load calculations agree with the inspector since they are so bloated and usually come out to 80-85A. But I know that a 100A service can easily handle a 48A EVSE since our houses are all natural gas, and the maximum demand is under 10A.

Since many inspectors might not like this and there might be a disagreement, I would like to be sure that the data I submit is proper.

The changes you mentioned in the 2026 are interesting, I am going to read into that tomorrow.

 

[Birken Vogt]

What about the old way, install monitoring equipment for 30 days and get your own peak? Is that valid?

 

[JohnHess]

What about the old way, install monitoring equipment for 30 days and get your own peak? Is that valid?

That wouldn’t work so well for me, unfortunately. Most of the time I complete the installation within two weeks of the customer’s initial call. Doing my own monitoring would put the job off by 30 days.

There’s a few other reasons as well. In my area the only large load is air conditioning since everything else is natural gas. So if I did a 30 day monitoring during any of the cooler months, the inspectors would immediately say that it’s not going to work in the summer. Getting the information from the power company would be more authoritative as well as cover the whole year.

 

[brycenesbitt]

What about the old way, install monitoring equipment for 30 days and get your own peak? Is that valid?

Yeah, but.... seasons.

Note this is a well worn topic

Calculations for existing buildings - 30 Day Metering

Hi, I wanted to get a consensus on this topic because I have read conflicting arguments on how to calculate total load on a feeder using existing metering data and new load. Let's assume we have done a 30 day load study and have and multiplied the load times 1.25 as stated in the code, NEC...

forums.mikeholt.com

 

[Birken Vogt]

That wouldn’t work so well for me, unfortunately. Most of the time I complete the installation within two weeks of the customer’s initial call. Doing my own monitoring would put the job off by 30 days.

Well if you can't get a permit then there will be no job at all, so they can jolly well wait 30 days if they have a 100 amp service they do not want to upgrade. I'm sure you will already know well enough whether it will pass or fail anyway.

There’s a few other reasons as well. In my area the only large load is air conditioning since everything else is natural gas. So if I did a 30 day monitoring during any of the cooler months, the inspectors would immediately say that it’s not going to work in the summer. Getting the information from the power company would be more authoritative as well as cover the whole year.

Code addresses this in 220.87(1) Exception

Take the max demand and add in the AC if the 30 days you picked does not include AC.

I know my poco has 15 minute demand for commercial but not for resi so we are out of luck there.