This is a great topic because it still gets misunderstood far more than it should. A lot of people hear the phrase selective coordination, then immediately start tying it to a fixed time band like 0.1 second or 0.01 second as if that applies everywhere. That is where things start going sideways.

The problem is not that people are trying to do the right thing. The problem is that they are borrowing language from one part of the Code and dropping it into another part where it simply does not belong. That is how bad interpretations get repeated enough times that they start sounding like fact.

In NEC 2026, Section 700.32 requires emergency system overcurrent protective devices to be selectively coordinated with all supply-side overcurrent protective devices. That is the part many people either skip over or do not fully appreciate. The requirement is not just about downstream branch devices and feeders. It reaches upstream as well.

In plain language, the Code is expecting the protective device closest to the fault to operate first so that the rest of the emergency system stays in service to the greatest extent possible. That is the entire point of selective coordination in an emergency system. When a fault occurs, you do not want a larger upstream device taking out a major portion—or all—of the system unnecessarily.

This is where the discussion needs to be precise. Time absolutely is part of the NEC when it comes to selective coordination, but that comes from the definition of Coordination (Selective) in Article 100—not from Article 700 assigning its own fixed time threshold.

In other words, the Code does consider time because selective coordination has to exist over the full range of available overcurrents and the full range of overcurrent protective device opening times associated with those overcurrents. So the issue is not whether time exists in the Code discussion. It does. The issue is whether Article 700 gives you a special fixed value such as 0.1 second or 0.01 second, and it does not.

The 0.1-second concept people often cite comes from Article 517, specifically the healthcare essential electrical system rules. That is a very specific occupancy-based requirement. It applies in that context, but it should not be casually imported into general Article 700 emergency system discussions as though it were the universal benchmark for all selective coordination requirements.

One of the most overlooked parts of this entire discussion is the supply side. People will spend all day looking at branch breakers and feeder devices, but if they ignore the upstream protective devices, they have missed one of the most important parts of the requirement.

That matters because the upstream device is often the one that can wipe out the bigger portion of the system if it operates before the downstream device that should have cleared the fault. When that happens, the emergency system may technically exist on paper, but it is not performing the way the Code intended it to perform when a real-world fault happens.

A casino is a great example of why this matters. In a facility like that, loss of emergency system continuity is not a theoretical problem. If one upstream device trips out of sequence, you can lose much more of the system than the original fault ever should have taken down.

That is exactly why the coordination conversation has to go deeper than “did we pass plan review?” A system can look fine in a submittal package and still fail the real test if the protective devices are not actually coordinated the way the Code intends.

One additional point worth saying clearly: this discussion is about the coordination of overcurrent protective devices serving emergency systems. It is not an attempt to blur the differences between emergency systems, legally required standby systems, optional standby systems, or healthcare essential electrical systems. Each of those has to be read in its own context.

It is also important to keep the terminology clean. The phrase essential electrical system is tied to healthcare installations in Article 517. Not every emergency system is part of an essential electrical system, and not every special rule from Article 517 can be dragged over into Article 700.

I think this is one of those areas where the industry sometimes overcomplicates something the Code actually says pretty plainly. Article 700 requires selective coordination. It includes supply-side devices. Time is part of the conversation through the Article 100 definition. But Article 700 itself does not hand you a special fixed 0.1-second or 0.01-second limiter the way some people keep trying to make it.

Once you keep Article 700 in its lane and Article 517 in its lane, the fog starts to clear. Then the conversation gets a lot more productive because now you are dealing with what the Code actually requires instead of repeating a rule from the wrong article.

At the end of the day, this is not just about making an AHJ happy or getting a stamp on a set of drawings. This is about whether the emergency system will perform the way it is supposed to perform when people are depending on it most.