Overcurrent Protection and the 25-Foot Feeder Tap Rule

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Sean White gave an NEC training at this year’s ASES Convention. Video from that presentation is included in our updated free course, “Introduction to Solar PV Design, Installation and Code“. But there was some content that was too advanced for an intro class, so we cut it and here’s one example of that.

Below is a transcript of Sean’s presentation that you can watch in the video above.

Video Transcript: Sean White explains the 25-Foot Feeder Tap Rule

What we have here is what’s called a feeder. And so a feeder is going from the feeder breaker and the main service panel, or it could even just be one breaker, go into the utility, but we’re going to call that a feeder because there’s protection. And then it goes a long distance there, and then it’s going to a sub panel.

So let’s call that the feeder, but we could also even kind of look at this as being a feeder. You know, it depends on the way you look at it. You have to look at these things from different angles. And this, these are things too that a lot of people don’t understand and people argue with. And in fact, when they first came out with this rule, we did a video with this guy named Mike Holt and Bill Brooks, and they were arguing with the night before of how, you know, which way was the right way. And I think it took a couple years before people really started agreeing and changing their minds and coming to a consensus on how to do that correctly. So what you have here, you have the feeder.

And this has got a hundred amps to it and we’re protecting this conductor here. So it doesn’t have more than a hundred amps going on it. And then all of a sudden, somebody pops in and inverter and they’re out in another 12 and a half amps here. So what do we do? So there’s not going to be any time where the current we’re going to have extra current going from that inverter.

Like if we turned off the sub panel still the most, you get going that direction is 12 and a half amps. So that’s not a problem, but going this way, if the sub panel was like overloaded and power strips are going into power strips, we could potentially have. 112 and a half amps going on this conductor.

And this is just for an example, maybe it would be a hundred amp converter, but just for this example, we’re doing 12 and a half. So what we do here is there’s a couple of different solutions how to deal with this. The first solution is if the conductor’s big enough, you don’t have to worry about it.

So you could swap out the conductor or maybe it’s already big enough before you ever showed up there. And we don’t use 12 and a half amps and the calculation, because when you’re doing wire sizing, there’s like going to be overcorrections. And so we take 12 and a half times 1.25, and that gives us 16.

And so we just need to make sure that this conductor can carry 116 apps. That would be nice and easy. If that conductor can carry 116 amps, then we don’t have to do anything. But if it can’t, if it’s a hundred amp wire, right. Here’s another solution. We put it over current protection device here.

And so we could put this one right here and that works really nice. You know, it’s like that, but it’s also kind of awkward to put, you know, it’s like this feeder was already there and then I’m going to go stick this a hundred amp over current protection device. So that’s kind of inconvenient. And sometimes a sub panel might already have a a hundred amp breaker in it.

So that would be the easiest way to do it. And so the question is, is can you do that because then, is this still going to be protected the way that you want it to? And so what it comes down to now is the consensus. It took them three years to decide how to interpret this, or, you know, like a lot of people in the industry, you can apply the tap rule, the solar tap rules that we’re going to look at in a little bit.

And so it would essentially what it comes down to is there there’s thing called the 25 foot tap rule. And so if you’re within 25 feet of this connection over to here, you can put that a hundred amp breaker in the sub panel. But if it’s greater than 25 foot, then if you had a really smart inspector giving you a hard time, they were not going to let you put it in the sub panel.

But when you get down to this stuff, it’s gets really difficult. And then also under engineering supervision, you can do it all kinds of different ways. If you had a professional electrical engineer, You could do it a different way too. And that’s actually there in the code. We have some different numbers, but same thing.

So there’s the feeder breaker and then there’s the inverter. And then if we’re within 25 feet, we can put it there in that position. This type of stuff that I’ve just shown you about tapping the feeder, I don’t see a lot of people even doing this, but those are the rules.