120V 240V Electricity explained – Split phase 3 wire

120V 240V Electricity explained – Split phase 3 wire


– Hey there guys. Paul here from theengineeringmindset.com. In this video we’re going to be learning how three wire split
phase electricity supplies work to get 120 and 240 volts. We’ll look at how the electricity gets from the power station
over to the property and then how it’s connected
around the property and each of the main components. Now, this system is used in North America so we’ll be using their
terminology and colour coding. If you’re from outside this region, then you can still follow along but your electrical system
will work differently. We’ve covered that in a separate video. Do check that out. Links are in the video
description down below. Remember electricity is
dangerous and can be fatal. You should be qualified and competent to carry out any electrical work. So, electricity is generated
at the power station which is usually located far away. The power station generates
AC alternating current and is connected to a step-up transformer. This transformer increases
the voltage to reduce losses and is connected to the grid. The grid carries high-voltage electricity over long distances, over
to the towns and cities. Once it reaches the towns and cities, it will enter a step-down transformer which will decrease the
voltage to a safer level. From here it will be distributed locally into smaller circuits on different streets or groups of properties. Connected to these distribution cables will be smaller transformers, usually pole-mounted which
again reduce the voltage down even further to a level safe
enough for residential use. On the property will
be an electricity meter which will quantify how much electricity has been used and the
electricity company will use this to invoice the property. The transformer will be connected
to the electricity metre by some cables which will either run above ground or underground. These cables will be two hot
wires and a neutral wire. Inside the transformer we
have two coils of wire. The primary coil is connected
to the power station and the second coil will be
connected to the property. The two hot wires are
connected to each end of the secondary coil and the neutral is connected
to the centre of the coil. Now, don’t worry about
that too much for now. We’re going to look at this
again later in the video to understand it. So, if we zoom into the property, we find a main service panel
which is sometimes called a load centre or breaker box. If we remove the cover and look inside, we first find the main breaker. This is usually at the top of the panel but it might be at the bottom. The two hot wires from
the electricity metre will connect directly to the
lugs on the main breaker. Coming out of the main breaker
will be two main bus bars. These are basically exposed metal sheets which carry electricity
to the circuit breakers. Notice I’ve shown the current flowing backwards and forwards. That’s because this is AC
or alternating current. These bus bars as well as
the lugs are not insulated, they are live or hot. The main breaker can be manually
flipped to cut the power to everything downstream
of the main breaker. The main breaker will also
provide over current protection to the property. It is rated to handle a certain
amount of electrical current passing through it, typically
between 100 and 200 amps. If this value is exceeded then
it will trip automatically to try and protect the property
and its electrical circuits. Inside the panel, we also have
a neutral and ground bus bar. This is basically a strip
of metal with lots of holes and screws in it. The neutral and ground
wires will sit in the holes and the screws will lock them in place. In this example, we have a block on either side of the panel. As this is a main panel, the two bus bars can be joined together so we have a connector bar between them. That way we have a shared
neutral ground bus bar. Sub panels must have their bar separated but that’s a topic for a separate video. From the electricity metre, we’ll have the neutral
wire connected to the lug on the top of the neutral ground bar. Notice the green screw. This is bonding the neutral
bar to the metal casing of the service panel. The purpose of the
neutral bar is to return the used electricity
back to the transformer. It does actually get a little
bit more advanced than that but we’re gonna look at that in a more advanced complex video, this is just covering the basics. So, the two hot wires will
provide the electricity and once it is used it will
return to the transformer via the neutral bar. It is still AC alternating current but to make it easier to visualize, I’ve only animated the current
flowing in one direction so you can see the path it will take. Now, if we were to take our multimeter and connect one lead to the bus bar and the other lead to the neutral bar, we would get the reading
of around 120 volts. If you don’t already have a multimeter then I highly encourage you
to get one for your toolkit. It’s essential for any electrical
testing and fault-finding. Links down below for which
one to get and from where. If we connect the multimeter
leads to the other bus bar and the neutral bar, we would again get a reading of around 120 volts but if we connect the multimeter
leads to the two bus bars then we get a reading of double
that at around 240 volts. So, why is that? What’s happening here? So, when we look at how the transformer is connected to the main panel, we have the two hot bus
bars connected to either end of the secondary coil in the transformer and then we take the neutral bus bar connected to the centre
of the secondary coil. So basically, when we
connect across the bus bar and the neutral bar, we’re only using half of the coil. So, we are only picking up
half the electrical voltage the transformer can provide. So, that way we get 120 volts. When we connect to the two bus bars, we’re connecting to the
full length of the coil. So, we’re picking up the full voltage which the transformer can provide. Therefore, we get 240 volts. If you want to learn
how transformers work, then check out our video
on transformer basics. Links for that down in the
video description below. Now, coming back to the panel
connected to the bus bar, we’ll have our circuit breakers. These will look something like this with is black plastic casing
and a toggle switch on top. The circuit breaker controls
the flow of electricity into individual circuits in the property. It can be manually
tripped to cut the power but it also has two important features. The first feature is overload protection. The circuit breaker is rated to handle a set amount of electrical current. When appliances or lights
are connected to the circuit they will each increase
the current in the circuit. If too many things are
plugged in and turned on then eventually the current will be more than the breaker can
handle and the breaker will automatically trip to cut
the power off to the circuit and protect the property. The second feature is
short-circuit protection. When the hot and neutral
come into direct contact with each other, the current will dramatically
increase almost instantly. When this occurs, it
creates a magnetic field which will trip the breaker and
cut the power automatically. Let’s have a look at
how the circuit breaker is connected to the electrical circuit. In this example, we will connect
to a simple light fitting which is controlled by a switch. We take the hot wire
from the circuit breaker and run this to the switch. We then run another wire from the switch and over to the light fitting. From the light fitting
we have a neutral wire which carries the return current back to the neutral bus bar. We take the ground wire
from the metal casing of the sealing box and the switch and we also join this
to the neutral bus bar as in this case it’s shared. The purpose of the hot wire is to carry the electrical current
over to the light fitting. The purpose of the
neutral wire is to carry the used electrical current
back to the main panel and then back to the transformer. The purpose of the ground
wire is to provide protection for a fault current. If for example, the hot wire came loose and touched the metal
casing of the light fitting, the ground wire provides
a low resistance path back to the panel. Without this path electricity
could flow through you if you touch the metal box. As the current flows
through the ground wire, it would increase the current and that will trip the
breaker automatically. So, the electricity flows
through the hot wire, through the main breaker,
down the main bus bar and into the circuit breaker. From there it flows along the hot wire, across the switch and light then back along the neutral wire and into the neutral bus bar
along the neutral bus bus wire and back to the transformer. I’ve animated this using
AC alternating current but to make it easier
to understand the path, I’ve shown it flowing in
a single direction now. We’ve covered lighting circuits in detail in a separate video. Do check that out. Links in the video description below. Okay, so what else might we find here? Well, we might find a
double pole circuit breaker which will let us connect to
both bus bars to get 240 volts which we can use the
power larger appliances like dryers, ranges and
air conditioning units. If we look at the dryer circuit example, we run the red hot wire
from the circuit breaker which is connected to the
main bus bar number two and we run this to the receptacle. Then we run our black hot
wire from the other terminal of the circuit breaker which
is connected to bus bar one and we connect that to
the receptacle also. In this case, we have the neutral wire connected between the neutral
bus bar and the receptacle which will allow us to get
either 120 or 240 volts from the outlet. Then we have a ground wire
to provide a safe route for any fault current. Now, we can either connect
across the two hot wires for our 240 volt connection or between the hot wire
and the neutral wire to get 120 volt connection. We’ll also very likely
find a GFCI circuit breaker which stands for ground
fault circuit interrupter. This will look something like this and depending on the model you buy, you will usually have a
pigtailed neutral wire connected to it. GFCIs are required on certain circuits where outlets are used for
places like kitchens, bathrooms, hot tubs et cetera. You should check with the
National Electric Code for exact details. The GFCI breaker has both
the hot and the neutral flowing through it. This way you can measure the
current flowing from both wires and ensure they are equal. If we took a standard outlet, we would take a hot wire from the breaker and connect this to the outlet terminal. Then we take the neutral wire
and run this back directly to the circuit breaker to a
specific neutral terminal. We then connect the pigtail
wire into the neutral bus bar. This will provide the return path. And of course, we run the
ground wire from the outlet back to the neutral ground bar. If we look at this example,
the current is flowing normally until the guy sticks a
screwdriver into the socket. The electricity then flows through him instead of the neutral wire. The GFCI is measuring the
current in the two wires and notices that these are not equal. It then automatically trips
the breaker to cut the power and save the man’s life. We might also come across
an AFCI circuit breaker. This stands for arc fault
circuit interrupter. These are required for
circuits feeding bedrooms, hallways, kitchens et cetera. Again, check with the
National Electric Code for exact details. AFCIs work also by being connected to both the hot and neutral wires. Inside this circuit
breaker is a circuit board which is measuring the circuit and monitoring for patterns which indicate an arc fault is occurring. These are installed
pretty much identically to how we saw the GFCI breaker. Under normal conditions, the
current flows through the hot back through the neutral into the breaker and through the pigtail and
back through the neutral bar. But if for example, a screw
was accidentally inserted very close to the cable
and removed the insulation to expose the copper wires, the electricity could now potentially jump across or arc from the hot
wire and into the neutral. The arc is incredibly hot and causes most residential
electrical fires. As the arc occurs, it
creates a unique signal in the electrical cable. The circuit breaker can detect this and will automatically
trip to cut the power. Connected to the neutral ground bar will be a thick uninsulated copper wire which runs out of the bottom of the panel and off to the ground rod
which is pushed into the earth near the property. Under normal circumstances,
no electrical current will flow through this wire. Its purpose is to dissipate
high static voltages from things like lightning. This way the electrical
systems and equipment is protected from damage. Additionally, we will
also find a bonding wire to metal pipe work in the property. This is to provide a safe
route for electricity to flow should a hot wire come into
contact with a metal pipe and this way will prevent
a person being electrocuted if they were to touch the pipe work. Okay guys, that’s it for this video but if you want to continue your learning then check out one of
the videos on screen now and I’ll catch you there
for the next lesson. Don’t forget to follow us on
Facebook, Twitter, Instagram as well as theengineeringmindset.com.

100 thoughts on “120V 240V Electricity explained – Split phase 3 wire

  1. ⚠️ Found this video super useful? Buy Paul a coffee to say thanks: ☕

    PayPal: https://www.paypal.me/TheEngineerinMindset

  2. As an Electrician in Australia I feel that America over complicated a LOT of things for no real benefit. Just go 240 throughout and be done with it like most of the world does…

  3. An interesting video, but you made one slight error. The green "Bonding Screw" is NOT for grounding the electrical enclosure. It IS for bonding the neutral bar TO ground. The Ground Bar is fastened directly to the enclosure and BONDED; the grounding electrode conductor from the grounding stake is connected to the Ground Bar. In most situations, the green bonding screw on the neutral bar is required; some systems use a strap between the neutral bar and the ground bar, but this is usually only found in Industrial electrical systems. Furthermore, although the NEC does not forbid it, in many regions of the US it is a violation to connect the load neutral wire to the ground bar, or the load ground wire to the neutral bar.
    Because proper grounding is so important, the NEC devotes and entire section of the code to this one subject, more than a hundred pages.

  4. China has many wind farms that are a long distance to where the power is needed. They use super high voltage DC, i guess it suffers less loss. Then they transform it back to AC. Just sayin.

  5. I am an electrical engineer and even though I know all of this from class and/or from doing it in my own house, I find this video entertaining and the best explanation I have seen yet. I’ll use this to help my buddies understand what I’m talking about! 😂

  6. In the 70s I was trying to find this information to hook up a welder. I had an idea that was how it worked but needed more verification before messing with anything. I could not find anything to show how it went. I asked electricians where I worked and they acted as if telling me this information they would instantaneously lose their job and status as electrician. I finally found a small picture in a book in a store showing a detail of how it goes.
    Young people have it way too easy to get information

  7. Split phase secondary winding in the step down transformer. Believe the two
    sides of the secondary winding are WOUND in opposite direction?

  8. Just a note here.
    Yes, breakers are meant to protect the "property" but more importantly it's all sized according to need. And the breaker size is determined by the wire size, a 10ga romex wire can only safely carry a certain ammount of amperage.
    VERY IMPORTANT to know for you do-it-yourself types

  9. With the supply transformer neutral being grounded at the pole, and we are adding in another grounding conductor or bond at the panel. We now have a ground loop for current to flow along instead of along the neutral? I don’t understand the secondary bonding of the neutral since it’s already done at the transformer pole.

  10. I need a good explanation of why some breaker boxes have plant ground and bonded ground at the same lug on the panel and others its separate.

    On the box where it is separate the left ground bar will have a copper wire run off to an earth ground ( rod driven into earth).

    And the right side will be plant ground.( Neutral)
    And sometimes the 2 are connected.
    He speaks about it briefly.

  11. If I understand you correctly both legs are on the same phase, I say this because you made no mention of them being different phases

  12. For the sake of god never neutralize youre elctrical system (i mean use neutral as ground), invest in a cheap grounding system like a 2m long ancer and screw it into the ground… Dont use frikin water tubes for this god damn it…seen a lot of these crap in life, i am not a professian electrican but i can solve problems on budget

  13. In the house where I grew up, the copper water main served as the grounding spike. Inside the breaker panel, besides the service wires, we had just one heavy-gauge bare copper wire connecting the ground bus to the water main, below the water meter. Since the water main was copper, sunk deep into the ground, it was ideal as both a true-earth grounding spike, and as a ground fault connection for the plumbing.

  14. What stops the return current of the neutral bar from going back out to the ground circuits if they share the same contact bar?

  15. I've looked for a concise video for quite some time that explained this in common language. So far, this is the best one. Keep up the good work.

  16. If only electricians labeled their hot AND neutral conductors that would be awesome. Im a licensed electrical engineer and every electrician working for me does this. It saves headaches in the future when replacing circuits.

  17. Great video!!!!! you mentioned in this video you have a video further explaing floating neutrals and bonded nuetrals more in depth, where can i find this. . thanks

  18. 1. #alert only 2 wires inters our #house . And our electricity is 220v.
    2. And large workshops has 3 wires in my city . What do you think is that? ?
    3. Also when someone touches the house electricity
    A. The person would be thrown too far like paper
    B . It will not release the person till he is dead! !
    What is that also?

  19. the ground wire goes directly house ground ; Neutral goes transformer's ground
    We use seperate bars for grounding rod and neutral
    Europe or I live in Turkey
    In your way you dont need 3 wire for your wall outlet. One cable for neutral and ground thats used in old buldings

  20. So why have a separate ground wire when it runs to the same place? Couldn't you just connect casing and such to the neutral wire and save some copper?

  21. Exactly what is "Used Electricity"? Regarding the ground to earth, in the US it's typically connected only to the residential gas pipe on the source side of the gas meter.

  22. Wonderful coverage. I love GFCI's especially around water. AFCI breakers are a solution in search of a problem and were code mandated just after invention, when only one company could make them. The NEC now protects Profits, machines, and people. In that order.

  23. Excellent video!
    Can we use the 240V dryer outlet in the US to run 240V appliances purchased from other countries such as U.K.? Or would you recommend a step up 110-240 converter?
    Thanks.

  24. You shouldn’t have the ground and neutral bus bars connected in the sub panel. They’re connected together at the meter box or main panel outside but they’re on separate bus bars inside at the sub panel

  25. Wow! Really good video. Simple, no-nonsense explanation.
    It's not easy trying to explain this to anyone, not in the know.
    One thing you might consider doing (and know it's gonna sound
    dumb…), is putting the wire illustrations closer together, and faintly
    show the wire jacket. Most people who are clueless about AC wiring
    can better understand the wiring part, simply by showing the wire, as
    it really is.

  26. I wish you would have commented on what happens in a typical residential electric system when you have split phase 240V but the loads on each 120V branch circuit are not balanced (equal).

  27. You know what I find strange, in USA and some other countries, the wall sockets / power points, do not have a switch like here in Australia. Why ? Very dangerous, especially when children can easily push a metal object into the wall socket. Makes no sense.

  28. People should stop worrying everything is going to be better and I believe we can all help each other if we focus on just that. Stop judging people.

  29. I thought i knew the basics… i know extremely nothing. You SIR would, and can be, saving lifes, or is it lives… either way… you are worthy of respect.

  30. Since current flows BACK to the Transformer through the Neutral wire, WHY is it called Neutral since it carries a flow of electricity? Isnt Neutral just as dangerous as HOT?

  31. My electrical knowledge stems from 12V DC automotive systems. I understand that when going from each individual bus bar to neutral you see 120V at each, but at 4:54 the meter is connected across the bus bars and shows 240V. My understanding of how a meter works tells me that it should read 0V if both sides of the bus bar are at 120V. The meter simply shows the difference in voltage potential between the two points, no? If they are both 120V, the difference is 0V. Going from neutral (0V) to each bar individually (120V each) should be 120V as you've shown, but unless I'm missing something I don't see how the meter will show 240V when going across the bars…

    Now if you connect a load to both bus bars in series it's definitely receiving 240V, but how would you read 240V from the meter without going from a common connection to both bus bars and neutral? Awesome video by the way, I've subscribed!

  32. I am not an electrician but have undertaken alot of electrical projects to code on my own.  It is stated that you have to be 100% confident in what you are doing as there is absolutely no room for error with electricity. I wish we had access to videos like this one 45 years ago in school. Straight up and straight forward… Thankyou

  33. Paul: I am impressed on how well you instructed this information, easy to understand. The animation is so well done. This is the best instructional video I have seen in a while. Good job, thanks. I subbed and will be looking forward to checking out more of your' vids when I have more time.

  34. Hi great explanation.
    Why the neutral is connected to the ground? Shouldn´t the ground cable go directly to the fiscal ground?

    And second, for the dryer receptacle, why do you connect the neutral if it is not needed? (The dryer will only use 220v so I think that it is not needed or is it?)

  35. Do you always need a neutral? My coworker says for our equipment thats 208V 1Phase we only need the two hots and ground. I mentioned the completing the circuit and letting the current to back to the bus bar, but they said its suppose to act like a perfect circuit and those nothing or close to nothing should flow back

  36. I came to learn about double pole circuits and 240V. I have a question about the 9:00 mark. So a 240V appliance has no neutral? Connecting a neutral steps it back down to 120V? Any link to the best video that explains this more in depth?

  37. Question please : 120 Joules of energy travel on each coulomb to the load
    which is a bulb that uses 120 volts. How do the coulombs become recharged
    if it is AC current? Also if the load is more than 1 amp it will need more than one
    coulomb? AC is push and pull the exact same ELECTRONS? Thank you.

  38. i found this video as to be as perfect as one can be,,,,,,,,,NOW i understand how the wires are hooked up to the transformer that comes into the house for 120 and 240,,,,,,,,,,that was ALWAYS SO FRUSTRATING not knowing how the transformer was hooked up and the path of the current flow……….NOW I DO,,,,,,,,,,THANKS SO MUCH………..it takes a special kind of person to TEACH OTHERS……YOU ARE THAT KIND OF PERSON………

  39. Wait 7:01
    You connected
    NEUTRAL and GROUND
    TOGETHER?
    why is separate and the connect together?
    How the power (used) going back to the panel with the NEUTRAL wire and connect with the ground wire is not doing that?

  40. hi there. Geat videos, very educative.
    would you kindly make one specifically on how to measure 230VAC from a transformer that has a neutral connector too?

  41. 7:35 i don't get that, how does the ground wire have lower resistance than the neutral wire ? don't all wires except specialty wires like heating coils have more or less the same resistance per foot/meter ? (give the same materials)

  42. PAUL: At 5:00 mm:ss, your secondary winding, at center tap, should FLIP rotation winding direction for 1/2 of the total secondary winding stack. Only then can 240Vac RMS be achieved. Sinewave for each 120V HOT leg must be 180° out of phase

  43. I have a question, could you please tell me what would happen if two hot wire touch in a single phase situation,would it spark or would it create 220 volts.

  44. Thank You! I've been out of service for almost 9 years, I have to work on my son's house, the breaker panel is a hillbilly's nightmare, I could not remember if the ground bar should be bonded to the neutral bar. Electrical isn't quite like a bicycle, some key points can get forgotten!!

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