why the hell do people put 15 amp receptacles on 20 amp circuits
all right as an electrician a lot of times you are going to come across
melted receptacles where a breaker didn't trip but a receptacle melted at a wall usually this
is going to be around Christmas time or you know sometime when it's cold and people are plugging a
whole bunch of space heaters in and they're over utilizing power at a very specific receptacle
how this happens is most of the time people are putting 15 amp receptacles into brand new houses
because code allows us to do that but they'll still put 20 amp circuits meaning there's a
20 amp breaker at the panel there's wire that's number 12 it's rated for 20 amps so it can carry
that much current through it but then you'll have 15 amp receptacles installed everywhere and
it's like why would we do that why would we say that we could run 15 amps worth of current
through something or we could run maybe 18 amps of current through something and the breaker
is never going to trip but that receptacle over time is not going to handle that and
it's actually going to heat up and start melting why would we allow that why would we allow that
code that's why code so let's break into the code 210.21 this is the 2020 national electrical code
under 2 10.21 b specifically it covers receptacles so b1 says a single receptacle on an individual
branch circuit a single receptacle installed on an individual branch circuit shall have an ampere
rating not less than that of the branch circuit so that means a single receptacle has to be 20
amps if it's on a 20 amp circuit so there's no problem there there's no question about that
but then we go down to b3 where it says receptacle ratings and it says we're connected to a branch
circuit supplying two or more receptacles or outlets receptacle ratings shall conform with
the values listed in table 210.21 b3 so if we look at table 210.21 b3 receptacle ratings for various
size circuits on the left hand side it's got a whole bunch of circuit ratings and amperes on the
right side it's got receptacle ratings so circuit rating again we're talking about the actual
uh rating of that circuit which is usually talking about the over current device the
breaker so if we have a let's say 20 amp circuit rating we have a 20 amp breaker 20 amp wire in the
wall you notice it says the receptacle rating that's allowed is either 15 or 20 amps why why
why not just put 20 amps so if you think about uh a service like an electrical service most of
the time we'll have like a 200 amp service on a house but if you ever take your ammeter and
actually clamp onto the conductors you might have like 20 amps flowing at any time the
likelihood of you ever having 200 amps flowing through that is going to be so rare
plus if you calculate a service a lot of people think that you're going to be
adding up every single breaker and it's like every breaker adds up to like 400 amps yet it's only
a 200 amp breaker and it's because most of the time you realize it's going to be underutilized
we're not using most of the stuff in there so we don't have to have that big of a service
so we can kind of de-rate some things a little bit that's one way we can think about this is a lot of
times you're not going to have 20 amps plugged into a single receptacle you might have 20 amps
you know on the entire circuit because you have things plugged in all over the place
so that's not actually putting any stress on one specific receptacle that's putting stress on the
entire circuit but it's all spread out so you're not going to have a 15 amp receptacle melting
because you don't have that one point of contact where you're making all of the metal
inside of that plug really really hot to the point where the plastic starts to melt
so a lot of times they know you're gonna have these things plugged in all over the place
but in specifically where they talk about the loads the permissible loads that are
able to be plugged into a receptacle that's where it gets a little bit interesting
so if you look at b2 we're still in 210.21 b2 it says total cord and plug connected load
we're connected to a branch circuit supplying two or more receptacles or outlets a receptacle shall
not supply a total cord and plug connected load in excess of the maximum specified in table 210.21b2
so if you look at the load that's being plugged in that's a little bit different thing than
just the receptacle itself so when you look at that table uh you'll see that you have a
15 or 20 amp circuit rating meaning either 15 or 20 everything in this table on this row is
going to be true you can have a receptacle rating of 15 amps meaning you have a 15 amp receptacle
but the maximum load that you're allowed to plug into that receptacle is 12 amps
so if you're only plugging in something that is up to 12 amps then it's not going to melt so that's
why it's okay to put a 15 or a 20 amp receptacle on that circuit because they're saying that you're
not allowed to plug any load higher than 12 amps in so there's just never going to be a problem
doesn't matter on a 20 amp circuit if it is 15 or if it is a 20 amp receptacle
but that's the problem most people are not electricians most people don't know electrical
code most people are cold in the winter and they just want their toes to be hot so they go and plug
in a whole bunch of crap so they might plug in two space heaters in the same receptacle and that
might draw like 21 amps well and you're thinking okay well a 20 amp breaker is going to trip right
no not necessarily so breakers are designed to trip at certain values so if something happens the
minimum value that is going to trip a breaker is going to be 20 amps if it's a 20 amp breaker but
we know that breakers have two different methods of tripping there's a thermal trip which is a slow
buildup of heat over time and for the thermal trip to even ever engage that breaker it has to hit 130
percent of its value so that's 24 amps on a 20 amp breaker so then if we uh that's just for heat so
21 amps being drawn on a 15 amp receptacle the metal inside of there is only really rated for
15 amps worth of current going through it so if you have 21 amps over a long period of time
it's going to heat that metal up so much on the inside of the receptacle that it's
going to start melting the plastic around it and that breaker is never going to trip it's never
going to sense that there's actually a problem because we're not hitting that 130 percent value
and then breakers also we've talked about this in other videos breakers have the 200 percent trip
as well and that's not a thermal trip that's a magnetic trip and that's usually if there's
a ground fault or a short circuit there's like a lamb like a huge impact um so it has to trip
at at least 200 percent so that's how you know like a breaker might not actually trip even though
you've got too much stuff plugged in but it's because we're banking on the fact that most people
most of the time are not going to be plugging a whole crazy huge load into a receptacle most
cords are rated for a certain thing so if you have a toaster that you plug in it might have
like a 15 amp cord because they know that toaster is not going to draw more than you know 12 amps
or whatever so they just put a 15 amp cord on it so when you're plugging that one device in
there's not going to be a problem but there's not a load that comes with a 15 amp cord on it that
you buy from a store that actually draws 23 amps that just doesn't happen they make these things
there's nema ratings manufacturers have to follow things but the problem becomes when people plug
multiple loads in and they get over the amount that it was designed for so if you didn't know
out there you're really only supposed to put on a 15 amp receptacle whether it's a 15 or a 20 amp
breaker you're still only supposed to put a 12 amp load into any one receptacle any one like duplex
receptacle so the other part that kind of mentions this it's at least worth noting because they kind
of word it in a little bit different way is in 210.23 a it says 15 and 20 ampere branch circuits
a 15 or 20 ampere branch circuit shall be permitted to supply lighting units or other
utilization equipment or a combination of both and shall comply with 210.23 a1 and 2. so a1 says cord
and plug connected equipment not fastened in place so not actually an appliance that's like stuck in
place something you just it's like portable like vacuum cleaner toaster or something like
that the rating of any one cord and plug connected utilization equipment not fasted in place so shall
not exceed 80 percent of the branch circuit ampere rating a lot of people confuse this to think oh
you can't load circuits up more than 80 of the breaker rating that's not what this is saying
it's saying any device that you plug in shouldn't be more than 80 of that specific circuits rating
that branch circuits rating so it's the same thing if we look at how they said in table 2 10.21 b2
on a 15 or 20 amp circuit that with a 15 amp receptacle they're saying basically we don't want
you to plug anything more than 12 amps in or if you look at a 20 amp circuit with a
20 amp receptacle you don't want to put anything more than 16 amps that's a single load plugged
into this thing and 16 amps is 80 of a 20 amp circuit so it's saying the same thing
uh 80 is the same thing as whatever is in this table down here for 16. so it's not saying that
you can't that you're like supposed to leave extra room a lot of people think that too like you're
supposed to leave 20 so like if more things get plugged in that's not what they're saying
it's specifically a thing that you take and plug in shouldn't exceed a certain amount
but again we're electricians we might know that mr and mrs homeowner mister
are going to plug stuff in wherever people are going to plug stuff in so
my rule of thumb is generally with commercial i'll always put 20 amp devices in on 20 amp circuits i
don't ever do anything like this residential i might do 15. the other thing reason why people
do 15 is because it saves a lot of money 28 receptacles versus 15 amp receptacles there's
they cost more there's more metal there's a little bit more stout so they cost more plus
they're just marketed as a bigger number so they cost more really is is probably more to do with it
than anything but with a you know home depot places like that they sell in bulk they sell
15 amp receptacles so you're even getting a cheaper pricing just because you get
sales they sell things in 15 amp all the time so more put people put 15 amp receptacles in homes
especially if you're putting like 300 or like 800 if you're doing some big custom home that's
a massive difference between you know 15 amp 20 amp receptacles that's kind of why people do it
but code does allow us to do it you just got to understand the why behind doing it but you do
need to know that people if especially if you're in like really cold places they're
going to be plugging space heaters in so maybe that's something you take into account
and give them dedicated circuits with a single receptacle so they can only plug one load into it
or maybe if they wanted two space heaters in an area give them two single receptacles on two
dedicated circuits that are 20 amp with 20 amp space heater you know single receptacles then
you're just not going to have a problem and then the rest of everything else you could use 15 amp
but you don't even have to do that because of code but always remember code is the minimums it's just
minimum safety minimum you know protection for people and equipment and things like that so
you can kind of do whatever you want as long as you're staying within code but
it is good design good practice to to probably just put 20 amp receptacles everywhere because
then nobody's going to have a problem you've kind of over built the circuits and that's best
case scenario but it all comes down to the fetia right like the the the dollar so that's why hope
you got something out of that so that is it if you want to know a little bit more about how breakers
work i actually have a video right here it goes over the whole 130 200 thing and actually crack
opens breakers and we talk about how a breaker actually works and if you want to know about
specific breakers like we talk about arc fault ground fault and dual function breakers click this
video right here so i love you crazy people thank you so much for your attention make sure you sub
super helps me out like the video if you liked the video and i'll see you in the next one