Spot the Code Violation

How to interpret client requests when AHJ corrections become a game of telephone

I received a request from a new client to provide load calculations for a commercial project - the original plans were drawn by another company. This is what the client said:

The city got back to me and the city wants Load Calcs on the SES that justify the service is able to handle the back feed of the solar.

I don't know of any part of the NEC that requires load calcs in order to justify the solar backfeed. So let's take a closer look at the backfeed they are proposing:

These aren't my plans, so don't come for me

They are proposing a 120.6A backfeed on a 400A buss bar. However, the max allowable rating is 80A for a 400A buss. That's the basics of the 120% rule. So how did they justify this?

Using NEC 2023 code references in an NEC 2020 jurisdiction is another fun quirk of these plans

The original designer thought they only had to abide by the Feeders section of the NEC.

However, all points of connection have to abide by the criteria of 705.12. So the feeder connection must comply with the Feeder rules, and the busbar connection must comply with the Busbar rules.

• Feeder rules: NEC 2020: 705.12(B)(1)) / NEC 2023 705.12(A)

• Busbar rules: NEC 2020: 705.12(B)(3) / NEC 2023: 705.12(B)

Methinks they thought they could avoid the 120% rule entirely with this method.

So coming back around to the original question - why does the client want load calculations? At this point, I'm guessing that they either need:

• A) Load calculations to justify a main breaker derate, for the 120% rule

• B) Panel schedules to use The Sum Rule (instead of the 120% rule)

Since I know everyone hates a main breaker derate (and breakers for commercial switchgear can be pricey), I took a look at the main switchgear to see if it was possible to use the Sum Rule.

However, the sum of all existing breakers on the main busbar is already at 480A, which doesn't leave any room for our solar breaker. So I gave the client a choice: either I could call out a MBD (main breaker derate), or I could rearrange their loads into a new subpanel to make the Sum Rule work. We ended up derating the main breaker, and I gave them the specs of the new main breaker they needed.

Now, you might be asking yourself: why didn't you just ask the client to begin with? And this answer is this: the point-of-contact absolutely did not know why he needed load calcs.

When I started working in solar, most people I worked with had at least a basic knowledge of the technical side. As companies get bigger and tasks get outsourced, the main directive is to do tasks quickly. More and more, I'm seeing a lot of unresolved, unplanned-for baggage being thrown at 3rd-party installers, who must resolve all pending issues in the field.

If my main purpose becomes 'get plans permitted quickly', then I would not consider things like: whether the components are in stock; project budgets; preventing inspection issues; and whether the installer will be able to install as-drawn. After all, I can leave those issues for someone else, right?