Basic Electrical Troubleshooting
hey, how you doing thanks for joining me. I'm gonna do is something a little bit different in this video what I'm gonna do is run through a presentation that will hopefully, help you gain some understanding of troubleshooting applications in different types of circuits.
I created this presentation for classes of mine to just kind of run through to give them an introductory into what voltage should I expect in different places and also we'll take a look at ohmic readings and how those kinds apply to troubleshooting as well. So the first thing we're gonna take a look at is we'll start out we're gonna put this over to a laser point here so we can use that we're gonna start out with our own meter and we have connected across an open switch and in series with that open switch we just have a light bulb okay so the first thing we're gonna do is we're gonna turn our meter on okay and what voltage do we think we should expect to see. So I'm gonna talk about something in this article called the voltage divider concept which if we think about a series circuit. The ohmic value of a component is going to be directly proportional to the amount of voltage that's dropped across that component so if we have a really high ohmic value, we should expect to see a really high voltage drop. If I have a low ohmic value I should see a low voltage drop.
I like to use the voltage divider when I'm doing things like troubleshooting especially when it comes to what voltage do I expect. So when we think about this open switch right now and we think about the ohmic value that it could be an open switch. It has an almost infinite amount of resistance or impedance across it okay. If I'm reading in this circuit an almost infinite amount of resistance or impedance I should expect to see the maximum source voltage available across an open switch like this, I should see expect to see 120 volts across this open switch. If I think about the potential right now my line one is connected to my red lead which means my red lead is at the potential of line 1, my black lead is connected to the potential of identified it's through a load.
We'll talk about the voltage on the load here in a second okay. It's through a load so I should see the potential across here of line 1 to identify which would effectively be my 120 Volts. So we're gonna move our meter leads over to our actual load or our lightbulb here okay. We know that we had 120 volts across the switch when it was in the open position we're gonna go back to the voltage divider principle if we think about this as a series circuit.
Hey if I had a maximum value of impedance here, well I know that a light bulb that's not burnt out has some value impedance but when we compare that some value of impedance may be eight ohms or something. Like that, to the infinite ohms of the switch, we can expect to see respectively almost zero volts and that's really what we do see here we should see zero volts across that component. Another way to look at it is my black lead is that the same potential as identified while my red lead well if we trace it back it's connected to this terminal but that's not connected to anything right that's effective. Like taking that red lead and just waving and waving it in the air I shouldn't see any voltage there.
There's no potential across the load right now okay so let's look at the next one we closed our switch we see that our light bulb comes on okay. Now, what voltage should we expect across that light bulb well if we think again about the value of impedance at this switch I know that a closed switch has very very low impedance and if we think of the voltage divider principle if I have very low impedance here I would expect almost zero volts here and that's what we expect across a closed switch. If it's connected to a circuit we should see zero volts if I move over to my load again this does have a value of impedance and when we compare the value of impedance to zero or almost zero ohms. Over here I can expect respectively that all of the voltage in my circuit will be out of my load now okay so we close our weed 120 volts okay. So my red lead is at the same potential right now as line one my black lead is at the same potential as identified but what happens if we remove the load my red lead is still at the same potential as line one and my black lead is still at the same potential as identified or ID.
what if we look at the meter reading we still see a hundred and twenty volts this kind of gives us a window into the fact that maybe voltage isn't always the best application or doing a voltage reading on a load isn't the best way to indicate that the load is failed all right because they told us 120 volts. Whether the load was there or not let's move to the next situation we have our switch closed we have our light bulb energized what could we expect to see across this reading right now. Across this, a closed switch again very low impedance across a switch means we should see very low voltage across that switch 1.1 or if I think about potential right now my line 1 or my red lead is at the potential of line 1 but my black lead is also at the potential of line 1.
This means there is no potential difference between these two which gives us our zero volts reading on our meter what about now we got two switches connected in parallel controlling the same load, okay we won't talk about the functionality of this realistically. We would have to have both of these switches in the open position to turn the light off and either one of these switches would override the other okay. But for what we're talking about what voltage could we expect to see this comes back to having an understanding of if let's call it equivalent resistance in parallel. If I have two loads connected in parallel I know that the equivalent resistance of those two loads will be less than either of these two hey they do not really load they are switches but it still applies to switches as well. If I have two closed switches that are essentially the same point all of this is exactly the same point so like previous.
I would see zero potential across these because both of these leads are at the same potential as line 1 and that's what we see is one point 1 million volts right and another thing to watch for on this auto-ranging multimeters is to make sure you're paying attention to the little prefixes that pop up on the screen because 250 millivolt is a lot different than 250 volts 250 millivolts is effectively zero.
I can get more voltage on the meter just by waving the leads in the air but make
sure that when you're expecting 250
volts you're not reading 250 millivolts
okay so
let's open this switch up one of these
switches connected into this parallel
group right here is open we're gonna
decide what do we expect to see with a
light bulb and what do we expect to see
with a voltage reading across our switch
okay so again if we think about that
parallel impedance equivalent this
switch right now is closed which means
it has effectively zero ohms of
impedance if it's connected in parallel
to this open switch and I have my meter
across that group I'm going to read
effectively less than whatever load is
connected in parallel that's one way to
look at it okay so we should see if I
have 120 volts applied right now line 1
is connected to my red lead but it's
also through this closed switch
connected to my black weed so they're in
black leads so there's there again the
same potential we should see the zero
volts across my switch configuration
which means I should see maximum voltage
or 120 volts across my load so if we
were to put our leads across our load
right now we would see 120 volts okay so
let's look at our next configuration so
we've taken the switches at a parallel
now we've got them connected in series
we have one switch closed and one
switched open and we notice that our
load is actually de-energized right now
so let's think about the voltage divider
first of all okay so I have zero volts
across my switch right now are sorry
zero ohms across my switch I should
expect to see zero volts across here as
well but there's another way to look at
this to line one my red lead is at the
potential of line one my black lead is
at the potential of line one as well
right so we should expect to see zero
volts across that closed switch if we
move our leads across the open switch
well that line one that red lead has the
same potential as line one and my black
lead has the same potential as
identified now and again we have that
almost infinite resistance here or
impedance I should see the maximum value
of voltage across this switch or a
hundred and twenty volts if I move my
leads over to my light bulb hey again if
I'm seeing a hundred and twenty volts
here
or maximum impedance here Hey with
respect to that almost infinite
impedance here
I should see almost zero voltage here
which we do Hey and then if I take my
leads and I have my black lead here if
we look at that it's connected to the
identified so the black lead is at the
same potential as identified while the
red lead way over here is connected to
line one
so my red lead is at the same potential
as line one my black lead is that the
same potential as identified so
effectively I'm just reading straight
across my source voltage and that's
exactly what we see is that one twenty
volts
let's open up both switches yeah so
again if we look at where my red lead is
it's in direct contact with line one so
it's at the same potential as line one
and my black lead is at the same
potential as identified so I'm reading
again source voltage if we look now this
one's a little bit trickier we have to
think of this black lead is still at the
same potential as identified but if we
look at where the red lead is it's kind
of connected to this portion of the
circuit that's just kind of floating in
the middle of the air right there is no
potential here when I say no potential
I'm not saying we have 120 to zero I'm
just saying it's like this lead isn't
even in the circuit at all okay so this
would be effectively like holding one
lead to identified and the other one
just waving it around in the air you're
not gonna read any voltage here and
that's exactly what we see on the meter
screen okay let's switch it up okay
we're gonna go away from the light bulb
and we're gonna look at just a simple
control transformer and we're gonna
actually apply this to both sides of our
load in previous videos I have gone
through kind of the transformer action
of how transformer works over here I
just have what's represented is I just
have the symbol for our inductor right
we have in between H 1 and H 2 we have a
coil and in between X 2 and X 1 we have
another coil right we have our primary
or high voltage side and we have our
secondary or our low voltage side and
they share a common core as when I
energize this transformer what it's
going to do is the current
through the primary coil creating
magnetic field and that magnetic field
in the core will induce a voltage on the
secondary side of the transformer and
this is just meant to be a 120 step down
to 24 volt control transformer
okay so we'll use it to kind of run
through similar examples to what we did
with the light bulb so the first thing
we're going to start off with here is we
have our open switch that controls our
transformer just like our light bulb
okay we know that our light bulb had a
certain amount of impedance we know that
it's more than zero but we know that
it's far far less than infinite if we
think about our open switch our open
switch has almost infinite so again back
to the voltage divider principle I can
say safely that my almost infinite value
of impedance across my switch means I
should have maximum voltage available or
120 volts if I move my leads over to the
primary coil on my transformer between
h1 and h2 I know that my switch has
almost infinite impedance this coil has
considerably lower impedance than that
open switch I should see zero volts
across my transformer right now there's
no voltage applied to my transformer
again another way to look at it is my
black lead is connected right to my
identified okay my red lead isn't really
connected to anything it's connected to
h1 on the transformer but because of
that I open switch again this is kind of
like holding the red lead up in the air
I'm not gonna get any voltage across
that okay so we should see zero volts
across our transformer if we close or
sorry well if we check out the secondary
side of our transformer we go back to
how that transformer actually works if I
don't have any current flow through the
primary side of my transformer I will
not have a magnetic field inside the
core and if I don't have a magnetic
field inside that core I'm not gonna get
a secondary induced voltage so I should
so I should expect to see on the
secondary of my transformer no voltage
right and I've just kind of shown the
meter leads out here connected out to
these outer rails to indicate if I had
any type of type of a load connected
across these I would see zero volts
across those as well zero volts induced
on the secondary of my transformer means
that I've essentially
no power supply for this circuit down
here okay so let's close that switch
okay and what voltage should we expect
across a closed switch if I have my load
connected as previously with the
lightbulbs I have almost zero impedance
which means I should have zero volts
okay and that's what we've got there we
move our leads over to the primary side
of our transformer now with respect to
this being effectively zero whatever
impedance I have on the primary side is
gonna be far greater than zero I should
expect to see whatever the maximum
voltage of the circuit is right so 120
volts I shouldn't read across that
transformer another way to look at it
again
h1 my line my red lead is at the same
potential as line 1 my black lead is at
the same potential as identified meaning
that I have 120 volts applied to the
primary side of this transformer okay
and again transformer action if I move
my leads to the secondary side of my
transformer both of my coils are intact
I should expect to see the secondary
voltage of my transformer now that is my
induced secondary voltage and again this
is a 24 volt secondary side so we should
expect to see 24 volts and again if I
move those leads out to these rails what
that's doing is just indicating if I had
any leads connected to those rails I
could expect to see 24 volts applied
okay and there we go there's our 24
volts so let's look at what happens in
this situation okay I've got my switch
is still closed over here but if you
look at what's happening here I have a
broken coil another way to indicate that
I have a broken coil or say that I have
a broken coil is maybe that coil is
burnt out okay before we move on I'm
just gonna kind of describe the
differences between an open coil and a
shorted coil because there's two there's
kind of three scenarios we could see we
have our normal functioning coil which
would have some value of impedance that
means it's a functioning load I could
have a burnt-out coil which means that
like if you think about a burnt-out
light bulb there's no path for current
anymore it has effectively infinite
impedance across this gap right here if
we think about a shorted out
well that's like saying we're gonna take
a wire and go straight from h1 to h2
okay that would mean that I would
effectively have zero ohms that'd be
like a closed switch across h1 to h2 so
when we refer to a burnt-out coil we are
effectively saying that that coil has
near infinite resistance okay so again
if we think about this I have 120 volts
applied I have a closed switch over here
which means zero ohms across this switch
which means I should have zero volts
here again my red lead is at the same
potential as line one my black lead is
at the same potential as identified I
still have a hundred and twenty volts
applied to my transformer okay so just
like that light bulb example previously
by burning out the coil we still have
that same measured voltage across this
coil so that's not going to indicate to
me that I have a bad coil okay I can
move my leads down to the second area of
my transformer and I know that again if
I have no path for current through that
that coil I'm not gonna build up a
magnetic field there will be no moving
magnetic field in my core which means I
should not expect to see induced voltage
on the secondary and I should see zero
volts on the secondary okay so zero
volts on the secondary would indicate to
me that there's probably a problem with
the transformer but we can isolate it
even further okay but I will first let's
take a look at what happens if we have a
burnt-out secondary so we know that a
burnt-out primary we're still reading
120 volts h1 to h2 and we're reading
zero volts x2 - x1 okay so if we look
now we have our secondary coil is burnt
out so h1 and my red lead is still at
the same potential as line one over here
my black lead and h2 are still at the
same potential as identified so my
reader should still read h1 to h2 120
volts so if you notice a broken primary
and a functioning primary both read 120
volts if we move it to the secondary
okay again I'm still and now I have a
current path through
primary so it is creating magnetic field
and we are seeing that magnetic field in
the core but because I have this broken
secondary coil I'm not going to see any
induced voltage out the secondary side
okay so what I should see is effectively
zero on the secondary side so if we run
through what just happened with a broken
primary we read 120 volts on the primary
zero volts on the secondary with a
broken secondary we read 120 volts on
the primary and zero volts on the
secondary so both of those indicated to
me the exact same voltages a that rate
there tells me that if I'm
troubleshooting a load maybe voltage
isn't the best tool to use hey there's
another setting on our meter that could
actually help us isolate which side of
our transformer is well broken or open
circuited okay so we are going to click
our meter over to an ohmic value reading
and before we get back to our
transformer we're just going to run
through what the difference is on a
meter are when we see Oh L pop up and
effectively zero ohms because the two
get confused quite often if I look at my
leads right now both of my leads are
held apart from each other if I think
about the value of impedance in between
these two it's gonna be near if it's
gonna be a lot it's gonna be near it
should be in the millions right so this
meter is designed to read probably up to
about a million ohms so effectively
anything over a million this meter is
gonna basically tell me that it's
infinite ohms and so if I take my meter
reading what should we expect if I have
my reader my meter leads held apart we
should see our meter indicate Oh L or
over-limit okay not overload or anything
like that Oh L indicates over the limit
range of the meter okay which in this
case it could be in the millions right
it's not infinite because if I had
enough voltage I could bridge this gap
we know that we can bridge air gaps with
enough voltage but the meter uses a
little internal power supply which is
not anywhere near heart or big enough to
bridge the gap so it just tells us that
it's over
if I take those two leads and I touch
them together I've effectively taken
that value of impedance from almost
infinite to almost zero in between these
two leads there is almost no resistance
or impedance I should see my meter
indicate almost zero it's not going to
be exactly zero because the copper or
the conductor itself in the meter lead
still has some value of impedance but
it's very very close to zero okay so
it's a good technique to use for example
when you're troubleshooting or trying to
figure out if a fuse is still good don't
just look at the fuse because they can
burn out inside the end caps where you
actually don't see that take your meter
put a lead on one end and a lead on the
other set it to continuity okay and then
check if you have zero ohms what that
tells you is there's continuity between
those two ends your fuse is still good
if you're reading zero ohms
it's like saying we have a closed switch
if my meter indicates oh L that tells me
that there is no path for current
through that fuse and then that fuse
would be indeed burnt out
okay so let's bring it back to the
transformer so right now we have our
burnt-out primary coil okay and you'll
notice over here I've got that switch
open in the previous slides we had the
switch closed to check the voltages one
of the things you need to remember and
it's imperative if you are doing
continuity checks on anything make sure
you were working with a de-energized
circuit these meters do not like to be
connected to energized circuits it's
very bad for them and so when you are
doing a continuity check or a resistance
check on a component make sure you de
energize the circuit it's best if you
can isolate the component because then
you know you're reading truly across
this coil right so let's think about
that right now if I have a burnt-out
coil and I'm checking h1 to h2 what
should I expect on my meter
I should see oh L indicated because it's
almost infinite value of impedance okay
if I was to move these meter leads to
the secondary well my secondary coil is
still good I should read something it
should be more than zero
should be less than infinity should be
significantly less than infinite and on
this one just as an example I've put 48
ohms in there okay that indicates to me
that the primary side of my transformer
has a burnt-out coil while the secondary
is still functional okay if we change it
so that we have a good primary coil and
a burnt-out secondary coil now if I
think about that ohmic reading on the
secondary it should be like the
burnt-out primary where I should see Oh
L indicated on my meter
okay so again just to kind of recap what
we've talked about here the voltage
readings that I got from a burnt-out
primary and a burnt-out secondary were
identical that would not indicate to me
which side of the transformer was
faulted obviously it would tell me that
if I had 120 volts applied to my
transformer and I had zero out there's
probably a problem with my transformer
okay and realistically what you do with
the control transformer is just chuck it
in the garbage and and buy a new one
okay but when we're talking about
components like this for example we can
actually isolate which side of the
transformer is burnt out by switching
over to our ohmic value or our
continuity check again when we had a
burnt-out coil on the primary it
indicated Oh L on the primary and
something on the secondary when we
switched it and had a burnt-out
secondary if I was to read h1 to h2
right now I would expect to see some
ohmic value greater than zero but less
than infinite okay on my secondary we're
indicating Oh al and that actually tells
me that my secondary would be burnt out
okay so hopefully this video has helped
you kind of expand your knowledge of
troubleshooting obviously I just used a
couple specific examples but again make
sure when you're reading components if
you're reading the actual loads don't
always trust the voltage because if I
had for example say a burnt-out gas
valve in a furnace the gas valve if I
was to meet her across the gas valve and
everything was working I would still see
24 volts across the gas valve even
though that little relay coil or
solenoid coil inside the gas valve could
be burnt out so always a good idea to
check with an ohmic value as well
if you can't isolate a component
obviously do that then you're not
reading accidentally across the
secondaries of the Transformer instead
of the gas valve but anyways again
hopefully this has helped you kind of
deepen your understanding of
troubleshooting thanks for joining me
and and we'll talk to you next time
