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g/electrical • Posted by u/ev_charger_eli •

Service upgrade for two Level 2 EVSE — when does 220.87 actually save the customer money? Code Question

Customer has a 1974 house on a 100A service, wants two 48A chargers. Standard load calc says upgrade to 200A, which means a new service drop, a meter main, and a POCO coordination window that is currently eight weeks out in this county.

Before I write that estimate I want to run 220.87 instead — the existing-dwelling method where you use 125% of the highest 15-minute demand over a year from the utility interval data rather than a calculated load.

Pulled the customer's SMUD interval data. Peak 15-minute demand over the last 12 months was 41A. So:

41A x 1.25 = 51A existing demand
100A - 51A = 49A headroom

Two 48A chargers is 96A of continuous load, which blows that out entirely. But with EVEMS load management (Wallbox or the Emporia unit) I can cap the pair at 40A combined and land at 91A total on a 100A service.

Question for people who have actually gotten this past an AHJ: does your inspector accept 220.87 interval data plus a listed EVEMS, or do they make you upgrade anyway?

💬 6 replies

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u/admin_jake ADMIN •
✓ Accepted Solution

You are asking the right question but you are solving it the hard way. 625.42 lets you size the EVSE branch circuit at the output of the energy management system, not the nameplate of the chargers. With a listed EVEMS set to 40A combined, your two chargers are a 40A continuous load — 50A after the 125%. Not 96A.

So the calc the inspector needs to see is:

51A (existing demand per 220.87) + 50A (managed EVSE) = 101A

That is 1A over on a 100A service, which is the entire argument. Drop the EVEMS cap to 38A and you are at 98.5A and it passes on paper with no service upgrade at all. Two hours of programming instead of eight weeks of POCO scheduling.

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✓ Solution
u/ev_charger_eli OP •

That is the answer. I was applying 125% to the nameplate instead of the EVEMS setpoint. 38A cap it is — the customer will never notice the difference on an overnight charge and it saves them about eleven grand.

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u/nec_nerd •

220.87 is legitimate and the language is not ambiguous — it is a permitted calculation method for an existing dwelling, full stop. The catch is the data itself. The section requires the maximum demand over a continuous 30-day period at minimum, and most AHJs want the full 12 months when the load is seasonal. Which yours is, in Sacramento, in August.

Print the interval data. Highlight the peak. Attach it to the permit application rather than waiting to be asked.

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u/ev_charger_eli OP •

I have the full 12 months, peak was a July afternoon as you would expect. Attaching it to the application is the part I was not doing — I was bringing it to the inspection and arguing. That is probably the whole problem.

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u/estimator_erin •

From the estimating side: put both options in the proposal. The managed-load version at the price you can actually deliver in two weeks, and the 200A service upgrade as an alternate. Some customers want the upgrade anyway because they are planning a heat pump and a range, and they would rather do the POCO dance once. Let them choose instead of choosing for them.

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u/panel_pete •

Only thing I would add — verify the existing panel actually has two spaces and a bus rating that can take it. I have had two of these where the 220.87 math worked beautifully and then the panel turned out to be a Zinsco. At that point you are replacing the panel regardless and the service upgrade is a small delta.

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