What up? Everybody? Welcome to another episode of Let's Ask Paul, the
podcast where you get to ask me any question you want on the National Electrical
Code, whether it's a calculation, whether it's just an opinion of the NEC.
Whatever you have do me a favor. All you've got to do is
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I do the Let's Ask Paul series. Let me give you a couple updates
really quickly before we get into today's episode, which spoiler alert, today's episode
is a calculation. So I know everybody loves calculations, but today is a
calculation question that somebody's sent in to me, and so we'll be going over
that, but I want to give you some updates. Okay. First,
as you all know, the Just Calculations video series is starting next month and
so we're working on videos for that right now. The thought is it's going
to be a video each week, a weekly a video, so it gives
you something to subscribe to be anxious each week for a new calculation and if
you want to get into that right now before the price goes up. It's
ninety nine dollars annually, but it's going to go up to one twenty five
when June rolls around, so you can get in now. You're locked in
that type of thing. So all you got to do is go to fasttrackstv
dot com or fasttrackstube dot com and go on and subscribe. Now you take
advantage of it while it's ninety nine bucks before it goes up when that exclusive
series comes out, and you'll see a lot of changes coming in June to
fast Tracks Tube. It's a premiere platform and we've spent quite a bit involved
in development of the platform and how it works whether it's on the mobile or
on a desktop. So we're really excited about that platform. So that's going
to be our exclusive video platform, so that's exciting to get ready for that.
Also, we do have a bunch of new mert that's available over on
our website fasttracks system dot com that's fas T t R A x S Y
S t e M dot com. So please do me a favorite check that
out. And of course we still have Electrician Pride Electricianpride dot com that has
a bunch of swag as well, if you're interested. Okay, so let's
get into the day's episode. So on the day's episode, somebody sent in
a question that says, Paul, can you explain the optional calculation for schools?
And so I figured I'd take a good opportunity to do that here in
a podcast. Now, granted, a lot of people are visual earners,
and most of the time calculations, it really takes a visual to kind of
get it. However, when it came to schools, the more I looked
at it, it lended itself to be okay for a podcast because it's basically
some concepts that you can valid by looking at the table, and all I'm
really doing is explaining it to you. So if you're driving in the car,
you're listening whatever, you don't need to watch the car in front of
you, don't need to worry. You can go back and look at the
tables that I'm going to be talking about in your codebook you when you're done,
I am out working out of the twenty twenty three edition of the NEC
So I need to make that clear first. It's the twenty twenty three edition,
and we're gonna be looking at twenty eighty six for schools, and we're
gonna be looking at the table to twenty dot eighty six the optional method,
Right, that's what we're going to be looking at, all right, And
the example that we're going to be using today as well comes out of Link
because I wanted to be able to since it's a video, I mean,
excuse me, since it's a podcast, I want and I wanted to give
you a direct reference. So the beautiful thing is that in Link, which
is a product that comes from NFPA, it's a codebook in your pocket.
Basically, the example that they give in the enhanced content is the one we'll
talk about, because again it just emphasizes how simple this is. But again
people get confused at the process. Okay, so we'll break it down for
you, all right, So let's go on and look at the code.
I'll read it to you since I know it's a podcast, and I will
break down the sentences and give you extra in depth explanation where necessary on this
one. But this is the optional calculation for schools. Now, remember this
is optional. You can always use Part three, which we refer to as
this standard method, but is the general method other than the optional method.
So you're given permission and you'll see where it gives you permission here to do
this, to use the optional but you know you need to know how to
calculate the standard method. So basically it's adding up. The thing is,
it's still a non dwelling application, right, You're still adding up if there's
any multi outlet assemblies, You're still adding up the cooking appliances, commercial cooking
appliances. You're still adding up all these loads as you normally would, and
you would apply the general lighting demands as you normally would. All that stuff
still applies if you're doing the standard method, and you need to understand how
to do the standard method, because you're going to need to size the neutral
using the standard method. Why because two twenty sixty one, which is for
neutral sizing and loading, is under Part three. It's not under Part four
where this optional method is. Now, I think what most people do,
like you know the designers if they're going to use this optional method that we're
going to talk about today, I think what they probably do is just size
the neutral full size and don't worry about the calc you get me. They
just go mascrew it. It's more trouble than it's worth, and the bigger
the better. Size it for that and be done with it. That's probably
what I see the most. But you do need to know that if you
are sizing and neutral that you need do need to know how to do the
standard method, okay, or we should say the general method under part three.
Okay. I don't want you to lose sight as I explain how to
do the optional that it is so important to understand how to do the regular
calculation, and I think people get overwhelmed by that. But it's just a
piecemeal process. Apply your demands for your outlets, uh you know the apply
you know receptor outlets, toply your apply your demands for your general lighting.
You're cooking all those type of things. It's just like you normally would do.
But I think people get overwhelmed by it. The optional method obviously is
so much easier, and it's really based on you taking all of the loads
and just adding them all up. Okay, just taking all of the connected
loads and just adding everything up and then applying the demands that you have here,
so it makes it easier. So I think that's what most of the
engineers who design it do. They just take all of the loads for the
various equipment, just add everything up and then apply this one big, allowable
optional method to that, and that's how they size the service for the school.
Okay, all right, so let's go one and read this out and
I'll break it down any piece that we need to break down. Okay to
twenty dot eighty six, and again, I'm in the twenty twenty three edition
of the NEC In case anybody's asking, or as I always get in comments,
people go, I'm in the twenty twenty I get it, but I'm
using the twenty twenty three. So just gotta work with me here, all
right. Two twenty dot eighty six Schools. It says the calculation of a
feeder or service load for schools shall be permitted in accordance with Table two twenty
dot eighty six in lieu of Part three of this article. We're equipped with
electric space heating, air conditioning, or both. Okay. So that's the
first part. So in order to be able to use this optional method,
you have to make sure that there is either electric space, heating of some
sort, air conditioning of some sort, or both. Okay, So you
can use the optional method. If they've got heating, you can use the
option method. They've got air conditioning, you can use the optional method if
they got both. Okay. And when you see it, say in lieu
of part three, that's saying that you're permitted to use the optional method.
You're not required. If you want to piecemeal and add everything up and apply
the demands we're necessary using part three, go for it. And like I
said, you would need to do that if you're sizing the neutral anyway,
unless you're just gonna make it full size and rock on. You get me,
okay, so let's move on. It says the connected load twich the
demand factors in Table two twenty eighty six shall apply include all of the interior
and xterior lighting power that would be all your loads, receptacle loads and all
that kind of stuff. Any specific equipment loads or whatnot. It says water,
heating, cooking, other loads that aren't pretty much in these ones that
i'm recommending. You still have loads you got to account for. Okay,
so maybe it's some ev charging that gets done at specific parking areas and that
type of thing. Right, those are other loads, it says, and
the larger of the air conditioning load or space heating load within the building or
structure. So basically, it's just putting everything in one big pile, and
then we're going to apply some demand factors to that. That's what it's basically
saying. But there's a unique approach to how we apply the demand factors.
So that's what we're going to talk about as we as we do this calculation.
But really think of it this way. It's really throwing everything into one
big bucket. Next, it says, feeders and service conductors whose calculated load
is determined by this optional calculation shall be permitted to have the neutral load determined
by two twenty dot sixty one. Okay, So while we might be sizing
the ungrounded hot conductors and everything based on this optional method, you still go
back and you're permitted. I mean, it could be full size if you
want, but you're permitted to go back and use the methods into twenty dot
sixty one to do that, So it just it's allowing you to be able
to do that for your neutral, which means you're going to have to do
a load calculation based on Part three in order to be able to size you're
neutral because you got to handle the calculated neutral load, So you have to
do a calcul on that, or you could again do what most people do,
They shortcut and just say screw it, full size neutral and this is
rock and roll. Okay, all right. Next it says where the building
or structure load is calculated by this optional method, feed within the building or
structure shall have ampacity as permitted in Part three of this article. So what
that means is you're not going to be using the optional method for any interior
feeders that are feeding other panels throughout the school. You're going to use the
standard Part three calculation for whatever loads that are going to be on that feeder.
Right, so if it's a home necroom or it's some other part of
the building, you're going to do specific load calculation using Part three for the
loads that are going to be seen by those conductors on that panel. So
it's basically saying you're not going to use the optional for that. That's totally
different. Now, it also goes on to say, you know, when
you do that, it says, however, the apacity of an individual feeder
shall not be required to be larger than the apacity for the entire building.
Now, the reason they say that is because if you're doing the entire building,
as you see, you're going to have this pretty significant demand factor applied
that. That's because the diversity the building is seeing. Those service or feeder
for the whole building is seeing this diversity across the board, whereas the individual
feeder that may be in the building going to a remote panel sayed somewhere else
saying now near the gym or home ech or auditorium or whatever it may be.
Those feeder conductors are only going to see the loads that are on that
So you're sizing for that load using Part three. But in no case,
since you don't have the same demands that you get for the full building,
the reduction that there could be a rare case where that feeder ends up being
larger. I don't see that happening. But if it's larger, all this
is saying is, you know what, it never has to be larger than
what that would be for the entire building. So that's all it's saying.
Now again, I don't see where you would ever have the remote panel being
larger than what it would be to the entire building, even after demands are
applied. But it just reminds you that never has to be larger, okay.
And then lastly it says this section which is again eighty six for schools
under to twenty shall not apply to portable classroom buildings. Okay. So one
of the other big reasons for that is the air conditioning example, for these
portable buildings, they have to meet Article four forty, and the lighting loads
for those would be considered continuous loads. And so the demand factors in two
twenty to eighty six simply do not apply to those portable classrooms, right,
so you'd have to do a separate calculation using these standard calculating method covered in
Part three for those portable classrooms. That's not going to be what we use
to do the overall school itself. You with me, So you leave those
portable things out. Now, they may get their own service, they may
get a feeder, and if they get a feeder things like that, then
you know, then you're going to size it what totally separately? Do it
total separate as far as the load is concerned when it comes to those but
you just all we're saying is you do not apply the the portable classroom buildings
are not added into this optional method. They don't get the demands applied to
them. Then they may get the value added to it using the part three
to the overall value, they just don't get to get lumped into this optional
calc You with me, Okay. In many cases, these portable classrooms may
have their own service to them, things like that, or they again maybe
a feeder. And if that's the case, then you calculate those at their
full value, and you're going to add that in addition to whatever your calculation
is for the school. That's just going to be in addition. Okay,
Okay, So let's go on and look in an example. So let's say
we're given an example of a hundred thousand square foot school and we're given and
we have to determine what is the VA per square foot, and they also
give us the connected load and they say that they've added everything up and it
ends up being two point five MVA and mving millions. So it's two million,
five hundred voltampires VA. Okay, So that's our VA, and we're
trying to find out that's our total that's our total VA that's been given to
us, and it's one hundred thousand square foot buildings. So we need to
break it down and find out what the demand factor is going to allow us
to reduce that VA per square foot down. So, but we have to
start out by finding what is the VA per square foot. So you take
that two point five million or two million, five hundred VA, two million,
five hundred thousand VA, and you divide that by one hundred thousand because
it's one hundred thousand square foot building, and that gives you twenty five VA
per square foot. Now, once you have that VA per square foot,
Now if you look at this table, this is what we're doing. We're
we're going to be reducing the VA per square foot. Okay, So we
want to get it from twenty five. We're gonna be able to apply some
of these demand factors to this connected load, and we're going to be dropping
down the VA to come up with an ultimate calculated load in VA. Okay,
you with me, all right? So if you look at the table.
It says zero to three VA one hundred percent of the VA and three
to twenty, which is the next seventeen over three at seventy five, and
then everything over twenty VA per square foot at twenty five percent. So remember
we had to come up with what the VA was per square foot and it's
twenty five. How do we get that? How do we get it?
Again? You take the two hundred and fifty thousand of actual connected VA that
they gave you, divide that by the square footage of the building, which
is one hundred thousand square feet, and that gave us twenty five VA per
square foot. Now we take that twenty five and now we can go work
in this table and at the end we'll convert it back to VA voltampires total
voltampiers. But what right now, we're trying to work an equation. Okay,
so what does it say zero to three at one hundred percent? So
we've got over three, so we know the first three at one hundred percent,
So we just take three VA and put it aside. Just stick it
to the side. So as it says over three to twenty, which equals
seventeen, right, twenty minus three is seventeen. So the next the seventeen,
we do at seventy five percent. So we take seventeen, we multiply
that by seventy five percent, and that gives us twelve point seventy five.
We lay that to the side, so we have a three VA at one
hundred percent. We have twelve point seventy five VA, which was seventeen at
seventy five percent, and then the last part that we have, which was
over twenty was five. Remember because the total overall VA per square foot was
twenty five, So that last five VA, we take it twenty five percent,
and that is five times point twenty five, and that is one point
two five VA. So then all you do, and I've got my calculator
here, and all you do is work it and add them all up.
So three plus twelve point seventy five plus one point twenty five that gives me
a total of seventeen VA per square foot. So do you see what the
demand factor did here? It dropped it from twenty five VA per square foot.
It dropped it down to seventeen VA per square foot. Okay, now,
once it dropped it down to seventeen, we need to now work it
back up using multiplication. We need to work it back up and find out
what is our total VA for this building, and then of course we can
apply the voltage and come up, you know, with what our amps are
for our service and whatnot. So seventeen times one hundred thousand, So I
do seventeen times one hundred thousand, and that gives me one point seven MVA
or one million, seven hundred thousand VA. Now that's quite a drop from
two million, five hundred to one million, seven hundred. Okay, So
that's eight hundred thousand VA. Quite a drop because of this demand factor allowance.
Okay. So once we have that total VA, then we can divide
that by whatever our voltage is for our service, and then we can determine
whether or not we need more than one service to a building because of the
allowances in two thirty dot two all those type of goodies. But that's the
next step you would go to with sizing your service and whatnot. But what
we needed to get was what is our VA to work with, and that
is how this table is utilized. Now there's other people that will do this
differently. They will apply the percentages differently and try to come up with the
same concept, but this is the way it's explained in the way it's given
in the NEC with how you do these to the VA right, Okay,
hopefully that makes sense to you. If you have any questions, like always,
you can always go to Paul Abernathy dot com and you can submit your
follow up question. Just let me know, be very detailed in what you're
asking, let me know the code cycle you're on, and there's anything you
want me to exp plain even more, feel free to elaborate on that and
I'll do my best to answer that for you. All Right, hopefully I
got something out of this episode, folks. Until next time, stay safe,
God bless and we'll catch you on the next Let's Ask Paul podcast