how do you tell the difference between a short circuit and a ground fault
all right so I had a really good question asked to me from Wayne Graham on YouTube on the how
do I replace a three-way switch video um he said Dustin can you make a video Lesson using
a chalkboard or my whiteboard going on the differences between a ground fault compared
to a short or a short circuit and how can a technician use his DVM or digital volt meter
to tell the difference in troubleshooting and ground fault compared to a short because it's
going to measure the same on a DVM meter in Milli Ohms a short circuit and a ground fault so how
does an experienced technician tell the difference so let's go over the Whiteboard and I'll talk
about it alright so first let's talk about what a ground fault is and what a short circuit is
so a lot of times when there's a problem on a circuit and a breaker trips and it keeps tripping
somebody's gonna be like oh it's shorting out or oh it's a short or it's like a dead short deadbolt
short direct shorts if you like there's all these different ways that we characterize shorts and
it's largely just because people often feel just say stuff right and you hear somebody else say
some stuff so you say some stuff but there's actually some like specific words that we need
to use and it's important to use them correctly so when we say a short circuit what we mean is
that there's a shortcut in the circuit the power is not coming from the source going through the
load like it's supposed to and getting back to the source it's somehow found a shortcut or a short
before the load so that is a short circuit now technically a ground fault can be a short circuit
but we call a ground fault a ground fault and it's specifically because we're talking about a hot
conductor that is grounded out that it's touching a ground wire it's touching a piece of metal
so that's an important thing to know it helps us to troubleshoot better because we instantaneously
know oh and that's what we're talking about that's where we need to spend our attention
when we're troubleshooting and not waste all this time chasing after a whole bunch of wires
that have nothing to do with the problem so a short circuit also tells us oh okay well
we know that there's a couple possibilities of what wires those could be but a ground fault
we know there's a different problem they can show up the same way which is what Wayne was
talking about in his question so how do you figure out what the difference is between
the two are just using your multimeter out in the field so I have a little bit easier way of doing
this he was talking about using his volt meter trying to read resistance values so let's see
what he's talking about first and foremost he's essentially saying that if he took his multimeter
and put it on the ohm setting turn the multimeter on he's saying if you take one lead and put it on
one conductor and another lead put it on another conductor you should be able to get some kind of
value out of this if there's a short circuit so let's say that this black wire has shorted
out to the white wire right that is not a ground fault because it has nothing to do with anything
metal it doesn't have anything to do with the ground wire it's just a short circuit so let's
say that this wire and this wire we're touching and this was no longer part of the circuit because
now this is the shortcut current's going to fly through here like at such a high speed that it's
going to trip a breaker that's what's happening at your panel is the breaker is tripping because
there's way too much current flowing through um and that 20 amp breaker is sensing like
180 amps or something like that or probably far more than that so what Wayne is saying is
if you were to like find the short or you were to take these wires and test them you're going
to have a certain resistance value because the conductors themselves have a certain amount of
resistance because they're a piece of matter you know there's little bits and particles that make
up this thing so naturally every conductor has a certain amount of resistance to it so if you
were to hook up and try to get a resistance value from this versus if you just took this black wire
and did the same thing here to the ground he's saying that you're going to get the same value
right if we have a breaker and we you run a black a white and a green out from a breaker all the way
out to a load well there's just as much copper on the black as there is on the white and as there is
on the green or the bare conductor so you're really going to get the same values whether
you test either way and every ground that's run out to something is running back to the neutral
up at the pole not at your panel made well if it's a service panel yeah they're going
to be touching we always Bond our neutrals and grounds together out at the service and then up
at the pole we want to be able to clear a fault or a short circuit we want to be able to trip a
breaker so essentially these grounds and these neutrals at this surface level are kind of like
the same don't confuse that I'm not saying grounds and neutrals are the same I've actually done quite
a few videos on how they are not the same but what I'm saying is the values that you're going to test
are going to be the same because they're really going to the same place so using resistance values
I don't find is an actual effective means of trying to figure this whole thing out if you have
a trip going on at an appliance and you don't know what's going on this is how the circuit is going
to be laid out at that Appliance now if this is a wash machine dryer this isn't a hundred percent
accurate right like you're not going to be running these wires straight to the element there's going
to be like a little board in here that's going to have like relays out here and it's going to have a
little bit of logic so if this is how it was wired current would just be always going this thing
would never turn off it would just be constantly running so in here we're running wires to usually
like a terminal strip and we put the black here and the white here and the red here and the green
here you know and then the the user input is what decides which wires connect and what does what
um but for the sake of like showing something I drew it this way so let's say that we have a short
circuit right inside of this piece of equipment for some reason the terminals burnt up and boom
the black and the white are now touching each other oh you stop it all right so now the load
is no longer a part of our circuit we have conductors that are just touching each other
we're tripping a breaker constantly every time we hit that breaker boom boom boom it's like
an immediate short it could be a ground fault how do you know it's not a ground fault without going
over here and opening everything up you're just standing back in the room hitting that
breaker and you're like damn it it just keeps tripping you don't there's no way of knowing
that it's just a ground fault or it's just a a short circuit to neutral you might be able
to like tell through years of being able to see things trip which if something is a is tripping
because it's like an arc fault trip there's usually like a little bit of a delay in the trip
um if something is like a direct short it might act differently if like the neutrals are tied
into other neutrals and it's like a really really long convoluted way for this thing to trip versus
just two straight conductors two hot conductor shorting together if it's a 220 short it's going
to be probably a lot more aggressive of a short than it is if it's just going to be a 120 volt
short so like as you go throughout time you're going to be able to see different behaviors and
Breakers and how long it takes one to trip um and that's that's kind of an indicator but as for this
situation for a situation where you have like just a ground that's the same length as a neutral it's
the same length as the hots they're not going to be able to tell a difference between whether or
not it's a ground fault or a short circuit either way you have current in this short circuit that is
going through this this portion of our circuit now the speed of light like in an incredible
amount of current so that breaker over here is just going to go boom it's going to pop open
really quick same thing down here if you have like a this red and this green shorted together
it's the same thing you can see that right so it's going to clear the fault the same exact way
so what I do is I take my multimeter and I put it on the continuity setting because that's more
important I don't care how many ohms of resistance there is on any specific circuit I would if I knew
the characteristics of the circuit and what all the wires were doing and everything if I knew
hey I've got this really short ground wire but this incredibly long convoluted neutral wire then
yeah you're going to get different resistance values and that is going to be of some value
because then you can identify oh the one that has a whole crapload of resistance on it is
the long Crazy Wire the one that has a very short resistance value is the the short one you know so
there is some validity in what he's saying but I think just a generally easier method to not have
to search so much to collect data to find that information is I just use continuity so I've got
a short circuit over here right let's do this again say for some reason like these two wires
are connected and these are not what I'm going to do is I'm going to put my meter still on the ohm
setting but I'm not looking for a resistance value I'm just looking for for continuity when I touch
the tips of these together that tone right there shows me that I have you can see that a complete
Loop right continuity testing always gives us a complete Loop if it doesn't make a sound then the
Loop's not complete so this is a useful tool I use this all the time for tons of different things but
what I would do is I would put one lead on black and one lead on white and that's going to show
me whether or not I have a complete Loop and if it does it shouldn't be the case there shouldn't
be a complete Loop until like Electronics kick in and you put values in and this thing starts
to turn and the loads on of course you're going to have container continuity when the load is on
but you shouldn't have continuity before that because the load is off the machine's shut off
so if there's still continuity in the circuit you should be able to test anywhere you could
test back at the panel too if you just have the panel cover off you go neutral to that specific
breaker the wire coming off of that one breaker if you've got continuity okay well there's a problem
if you're over at the motor itself you could do the same thing if there's continuity there if
there's a junction box in between somewhere don't take the wire nuts apart just stick your leads
down in the wire nuts and if you have continuity there shouldn't be continuity so you know oh that
is where my problem is you could do the same thing on the hots to check the two Hots if
there's continuity between them there shouldn't be continuity again until the load is connected
going through that element right because once you energize a load
this whole element here or this coil of wire connects to both of these and that's what allows
the motor to start working so in that moment while it is working you do have a complete
circuit and there is going to be continuity but when the load is not connected you're not going to
have continuity so you can check here if there's continuity on these two that means you're going to
have a 220 short but you can probably tell it's a 220 short because that's like a boom like a lot of
times you'll see Sparks Fly Through of panel cover with a 220 short you can see it with a 110 as well
it just kind of depends on the characteristics of the circuit but you a lot of people that have
been doing this a while can tell like holy crap that was a 220 short that was massive
um so what I would do the natural order of things is I'm always going to check to see if
it's a short circuit first item you don't have to that's just kind of what I do but then you would
do the same thing just check the ground and if there's continuity between hot and ground there
shouldn't be that means that this whole entire thing is the green wire right essentially when
you hook up an appliance or a light fixture or anything to the green wire it makes the green
wire the whole Appliance everything metal touching this is the green wire now so you could even touch
like the casing of this thing depending on if you know if the casing like is grounded you got to be
a little bit careful in making assumptions on touching metal in appliances because some
parts of the appliance might not actually be connected to the ground so it's always better
just go straight to the conductor but you know go to the green conductor go to your black go to your
next you know your red go to your uh your white see where the continuity lies you're probably
going to get continuity between your white and your green so don't be surprised by that if you
start testing that because again look they're all connected back at the end so they're using
a completed Loop you know to complete your your continuity test so that's it like that it's it's
way easier to just use continuity and not worry about what resistance values are and what's the
length of the conductor and how many ohms per foot is the certain amount of resistance or reactance
of that one conductor and go look through tables in your code book to try to figure all this stuff
out and you just don't need to do that right like I'm a big fan of trying to find the easiest things
to solve the problem the quickest and a really good method that I was taught by this old school
dude Johnny thank God I worked with you for a lot of years uh he said always find the knowns
when you're troubleshooting anything you need to find the knowns as many knowns as you can get even
if it's an extraneous amount of knowns that seem like it's not even important find as many knowns
so that way when you're sitting there in front of a problem you can knock off silly questions
basically because you've already checked certain things if you walk into a situation and you're
like I know something doesn't work cool that's one known that's that doesn't help you though do you
know what the amperage is when that load kicks on do you know if there's a short between any of the
two leads do you know uh what is the the short actually look like when you're out there what
is it doing at the breaker what's it doing at the load what's the conditions of the wire are
they charred are they black you know there's like a lots of information that you should be
collecting anytime that you're troubleshooting something and the more things that you can turn
this knob and test values everywhere and write all that stuff down and know what the circuit is doing
I mean there's a reason reason there's this many damn dials on these things because there's this
much information that you can try to find in a circuit and the more things that you actually
know about the circuit and what's happening even if you got to write it all down the better you're
going to be able to diagnose that because even if you were to call your boss later and be like
hey this thing's not working first thing you're going to do is start asking you questions like
what's what's the current you know like when you put your clamp on ammeter on what values are you
getting is there some kind of photocell somewhere is there time clock somewhere is there lighting
control system somewhere did you take this apart is this you know like they're trying to figure
out all of the different knowns that they would think about to try to get to narrow everything
down to like the simplest point so that's my recommendation for any of you experience techs
out there is get rid of all the knowns or to get rid of all of the unknowns get as many knowns as
possible and Whittle your list down it'll usually end up focusing you in on the exact problem
hopefully that helped help um there's a lot of different ways to do things in this trade and once
you start understanding how a multimeter works and what's going to happen when you do things
it's really going to help your troubleshooting a lot especially once you can kind of look at a
circuit and understand it from like a 30 000 foot View and then zoom in that's one thing I tell a
lot of apprentices when you're troubleshooting like you can't just be so focused in all the
time and only seeing what's in front of you without thinking about everything else or else
you're going you're going to be missing a lot of information so it's always really good to
be able to zoom out think about the whole circuit Zoom back in think about the appliance Zoom back
out think about how things could be working in the circuit Zoom back in test values but trying
to find as many knowns as as you can gather is going to help you figure out what your unknowns
are it's going to limit the amount of unknowns that you have so thank you guys so much for
watching make sure that you check out our Discord server join that if you want to be a part of our
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