what is available fault current  
what is available fault current  

all right so we hear this term  available fault current uh  
all right so we hear this term  available fault current uh  

constantly if you're on facebook forums or you  know just talking to people in general maybe  
constantly if you're on facebook forums or you  know just talking to people in general maybe  

they had a journeyman's exam or master exam or  something then they were like this available  
they had a journeyman's exam or master exam or  something then they were like this available  

fault current thing is something i keep coming  across or maybe you're just out in the field and  
fault current thing is something i keep coming  across or maybe you're just out in the field and  

your boss gives you this placard and he's like  hey you're at a commercial building we need to  
your boss gives you this placard and he's like  hey you're at a commercial building we need to  

put the the afc placard on to a service in  commercial and other than dwelling services  
put the the afc placard on to a service in  commercial and other than dwelling services  

we have to actually mark what the available  fault current for that service is so what does  
we have to actually mark what the available  fault current for that service is so what does  

that even mean all right first let's break out  the handy dandy 2020 national electrical code
that even mean all right first let's break out  the handy dandy 2020 national electrical code

go into the definitions and uh we have  well we have fault current and fault  
go into the definitions and uh we have  well we have fault current and fault  

uh ground fault so what are all these things mean  first of all let's just talk about what a fault is  
uh ground fault so what are all these things mean  first of all let's just talk about what a fault is  

fault is basically an accidental occurrence like  uh you know in a tennis match or so i don't know  
fault is basically an accidental occurrence like  uh you know in a tennis match or so i don't know  

i don't watch tennis but i feel like i've heard  the term fault before uh but fault is just like  
i don't watch tennis but i feel like i've heard  the term fault before uh but fault is just like  

oops that's not supposed to happen um so code  defines a fault current as the current delivered  
oops that's not supposed to happen um so code  defines a fault current as the current delivered  

at a point on the system during a short circuit  condition so not a ground fault not where a hot's  
at a point on the system during a short circuit  condition so not a ground fault not where a hot's  

touching a ground specifically a short circuit  but we can have a ground fault it's still an  
touching a ground specifically a short circuit  but we can have a ground fault it's still an  

oops or an accidental it's just a ground fault is  what we call when a hot touches ground or when it  
oops or an accidental it's just a ground fault is  what we call when a hot touches ground or when it  

grounds out we don't call that a short circuit a  short circuit is talking about the actual circuit  
grounds out we don't call that a short circuit a  short circuit is talking about the actual circuit  

where there's current flowing to a load so a short  circuit happens between hot conductors you know  
where there's current flowing to a load so a short  circuit happens between hot conductors you know  

ungrounded conductors or hot and neutral right  so like uh the the un grounded and the grounded  
ungrounded conductors or hot and neutral right  so like uh the the un grounded and the grounded  

conductor so when we're looking at short circuit  current or a short circuit is a type of fault it's  
conductor so when we're looking at short circuit  current or a short circuit is a type of fault it's  

just not a ground fault there's also arc faults  so arcing can happen between two conductors we  
just not a ground fault there's also arc faults  so arcing can happen between two conductors we  

have series arcs where we have like a break  in a wire or at like a terminal where we've  
have series arcs where we have like a break  in a wire or at like a terminal where we've  

landed something on a terminal in series it  can arc so that's a type of fault that causes  
landed something on a terminal in series it  can arc so that's a type of fault that causes  

a breaker to trip we could have a parallel arc  which is between two actual ungrounded conductors  
a breaker to trip we could have a parallel arc  which is between two actual ungrounded conductors  

or between two uh like an ungrounded grounded  so between two hots or between hot neutral  
or between two uh like an ungrounded grounded  so between two hots or between hot neutral  

it is taking a short cut it's basically the same  thing as a short circuit it's just an arc that's  
it is taking a short cut it's basically the same  thing as a short circuit it's just an arc that's  

happening between two conductors rather than a  direct short where they're touching each other  
happening between two conductors rather than a  direct short where they're touching each other  

so those are the kinds of faults that you might  come across and what they actually mean so what  
so those are the kinds of faults that you might  come across and what they actually mean so what  

does code say about available fault current so  available fault current or afc is the largest  
does code say about available fault current so  available fault current or afc is the largest  

amount of current capable of being delivered  at a point on the system during a short circuit  
amount of current capable of being delivered  at a point on the system during a short circuit  

condition so we're talking about a short circuit  condition what is the largest amount of current  
condition so we're talking about a short circuit  condition what is the largest amount of current  

that can flow during a short circuit at an  electrical service the reason we put that is  
that can flow during a short circuit at an  electrical service the reason we put that is  

that is the closest point to the transformer  so from the transformer we have our secondary  
that is the closest point to the transformer  so from the transformer we have our secondary  

conductors that come in they attach to our service  entrance conductors come into the service and  
conductors that come in they attach to our service  entrance conductors come into the service and  

boom they land on our breaker everything from  the breaker out can still have short circuits  
boom they land on our breaker everything from  the breaker out can still have short circuits  

and ground faults and everything like that but  the amount of available fault current is going  
and ground faults and everything like that but  the amount of available fault current is going  

to be based off of a couple factors and one of  them is the conductor size how much current can  
to be based off of a couple factors and one of  them is the conductor size how much current can  

travel through a tiny conductor versus a large  one a whole lot more current can go through a  
travel through a tiny conductor versus a large  one a whole lot more current can go through a  

large conductor so the availability for current  to travel the amount of current that can travel  
large conductor so the availability for current  to travel the amount of current that can travel  

in on a fault condition in a small conductor  that's way out in the field hooked up to like  
in on a fault condition in a small conductor  that's way out in the field hooked up to like  

a toaster or something like that there's not  much available fault current that can happen  
a toaster or something like that there's not  much available fault current that can happen  

compared to the amount of current that can  float in these service entrance conductors  
compared to the amount of current that can  float in these service entrance conductors  

imagine in a service coming off a  transformer we're hooking up like  
imagine in a service coming off a  transformer we're hooking up like  

parallel 500s i mean we're talking like multiple  massive conductors on per phase and then phase to  
parallel 500s i mean we're talking like multiple  massive conductors on per phase and then phase to  

neutral so when we figure out our available fault  current we're basically saying at this service if  
neutral so when we figure out our available fault  current we're basically saying at this service if  

these two incoming hot conductors line to line not  necessarily line to neutral line the line the most  
these two incoming hot conductors line to line not  necessarily line to neutral line the line the most  

amount of current would happen between two hots  not a hot and a neutral because we have double the  
amount of current would happen between two hots  not a hot and a neutral because we have double the  

voltage between two hots where we only have the  single amount of voltage between hot and neutral  
voltage between two hots where we only have the  single amount of voltage between hot and neutral  

so the available fault current is always a line  to line measure of if these two hots touch here  
so the available fault current is always a line  to line measure of if these two hots touch here  

what is that current how much current is going to  be allowed to flow in this bit of wire from the  
what is that current how much current is going to  be allowed to flow in this bit of wire from the  

breaker or wherever you know essentially from the  breaker if they were to short out at the terminals  
breaker or wherever you know essentially from the  breaker if they were to short out at the terminals  

back to the transformer so much current is going  to flow so much more than any other point on  
back to the transformer so much current is going  to flow so much more than any other point on  

the system because the conductors are the largest  you probably have a certain amount of length from  
the system because the conductors are the largest  you probably have a certain amount of length from  

the service so that's another thing to figure  out is how long are the conductors because the  
the service so that's another thing to figure  out is how long are the conductors because the  

the impedance or the opposition to current flow in  conductors the longer the current that conductor  
the impedance or the opposition to current flow in  conductors the longer the current that conductor  

is the more material there is for opposition  to happen so naturally you have resistance  
is the more material there is for opposition  to happen so naturally you have resistance  

or impedance i'm just going to call it resistance  for ease of understanding but the the amount of  
or impedance i'm just going to call it resistance  for ease of understanding but the the amount of  

resistance or impedance that you can have  in a conductor is going to increase with  
resistance or impedance that you can have  in a conductor is going to increase with  

the length of that conductor so the how close  you are to a transformer what the let-through  
the length of that conductor so the how close  you are to a transformer what the let-through  

current of that transformer is what the voltage  is whether or not it's single phase or three-phase  
current of that transformer is what the voltage  is whether or not it's single phase or three-phase  

um and the size of those conductors are all going  to determine how much current can flow if these  
um and the size of those conductors are all going  to determine how much current can flow if these  

two huge conductors just touch each other that's  what available fault current is and we have to  
two huge conductors just touch each other that's  what available fault current is and we have to  

figure that out for every service that's not  a residential service so typically three-phase  
figure that out for every service that's not  a residential service so typically three-phase  

environments maybe not three-phase but just  commercial environments industrial stuff like that  
environments maybe not three-phase but just  commercial environments industrial stuff like that  

so then if we look into uh 110.24 110.24 talks  about available fault current and field marking  
so then if we look into uh 110.24 110.24 talks  about available fault current and field marking  

of these panels so what it says 110.24a says field  marking service equipment at other than dwellings  
of these panels so what it says 110.24a says field  marking service equipment at other than dwellings  

so not houses shall be legibly marked in the field  with the available fault current the field marking  
so not houses shall be legibly marked in the field  with the available fault current the field marking  

or markings shall include the date the fault  current calculation was performed and be of  
or markings shall include the date the fault  current calculation was performed and be of  

sufficient durability to withstand the environment  involved so like a placard or something that's not  
sufficient durability to withstand the environment  involved so like a placard or something that's not  

going to like rub off the calculation shall be  documented and made available to those authorized  
going to like rub off the calculation shall be  documented and made available to those authorized  

to design install inspect maintain and operate  the system and then b goes into modifications so  
to design install inspect maintain and operate  the system and then b goes into modifications so  

even if you modify a service you still have to  update the available fault current calculation  
even if you modify a service you still have to  update the available fault current calculation  

and put the date and all of that stuff on it  so that is available fault current hope that  
and put the date and all of that stuff on it  so that is available fault current hope that  

answered some of your questions please leave  comments below any other questions things that  
answered some of your questions please leave  comments below any other questions things that  

you want me to do videos on i am spending all of  this year 2022 going through the comments and just  
you want me to do videos on i am spending all of  this year 2022 going through the comments and just  

answering your guys's stuff because holy hell  over the five or six years that i've been doing  
answering your guys's stuff because holy hell  over the five or six years that i've been doing  

this now there's been so many suggestions that  i can't keep up um so i've been loving doing  
this now there's been so many suggestions that  i can't keep up um so i've been loving doing  

this but please ask any of your questions below  love you crazies and i'll see in the next one
this but please ask any of your questions below  love you crazies and i'll see in the next one

Descant Music and Video
Descant Music and Video