Basic Electrical Troubleshooting

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