Connecting Line 1 to Line 2 without a load in between

[fourthindiana]

Preface to post: Through this post I am going to be referring to line 1 and line 2. When I write about line 1 and line 2, I am writing about electrical leg #1 and electrical leg #2 respectively. Perhaps electrical engineers are used to calling the lines of electrical power in a residence "legs" rather than lines.
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I'm a student at a trade school, majoring in HVAC. My instructor is an expert on installing, repairing, and maintaining both commercial and residential HVAC systems, but my instructor is only an HVAC technician, not an electrical engineer. One can be an expert HVAC technician without knowing what is happening in an HVAC system at the atomic/subatomic level. Therefore, my instructor cannot help me understand this at the subatomic level.In my HVAC class at the trade school, we have an electronic practice board which consists of two 115V legs of power and multiple relays, contactors, and other electronic parts and light bulbs at the top of the board. The light bulbs symbolize loads such as condenser fans, compressors, etc. In class several days ago I wired up the electronics practice board with an electrical wire going through a normally closed relay to connect line 1 to line 2. I don't know the exact words my instructor used, but my instructor said that using an electrical wire to go through a normally closed relay to connect line 1 to line 2 would cause some sort of electrical malfunction. My instructor might have said that connecting line 1 to line 2 through a normally closed relay would cause a short.

I have drawn a ladder diagram of such a system on a dry erase board. In the photograph at the top of this post is a ladder diagram in which I used a black marker to draw a wire connecting line 1 to line 2 via a relay without going through a load, and I used a green marker to draw a wire connecting line 1 to line 2 without going through a load or anything else. In the attached photograph, N.C. Relay stands for normally closed relay. In the attached photograph, L1 stand for electrical leg (or electrical line) #1 (which is 115 Volts), and L2 stands for electrical leg (or electrical line) #2 (which is also 115 Volts).

In the black (top) line on my ladder diagram, would the black line that goes through from line 1 through a normally closed relay and then to line 2 cause an electrical malfunction? If so, why would having a wire connecting line 1 to line 2 via a normally closed relay cause an electrical malfunction? If the black line going from line 1 to line 2 via a normally closed relay would cause an electrical malfunction, would the electrical malfunction be a short? What would be happening at the level of the electron (the atomic level) to cause an electrical malfunction?In the green (bottom) line on my ladder diagram, would the green line that connects line 1 to line 2 cause an electrical malfunction? If so, why would a line connecting line 1 to line 2 without going through a load cause an electrical malfunction? In other words, what would happen at the atomic/subatomic level to cause a malfunction? In other words, what would happen at the level of the electron to cause a malfunction?

 

[AZFIREBALL]

What size wire will you be using to connect Line 1 to Line 2 (size of black wire and size of green wire)?

 

[fourthindiana]

What size wire will you be using to connect Line 1 to Line 2 (size of black wire and size of green wire)?

I put the best answer I can give you in green, boldfaced font.

Since there is no load in either the black wire or the green wire, I did not think that the size of the wire would matter.

I don't know what the common wire sizes are.

Lets just say that I would be using the same size wires in these alligator clip jumper wires:
https://www.walmart.com/ip/10pcs-Alligator-Clips-Electrical-DIY-Test-Leads-Alligator-Double-ended-Crocodile-Clips-Roach-Clip-Test-Jumper-Wire/281918277?wmlspartner=wlpa&selectedSellerId=101001044&adid=22222222227104019967&wl0=&wl1=g&wl2=c&wl3=233343378231&wl4=pla-448948471917&wl5=9011112&wl6=&wl7=&wl8=&wl9=pla&wl10=126804364&wl11=online&wl12=281918277&wl13=&veh=sem&gclid=EAIaIQobChMI5-fY-crc3gIVnYWzCh0EyA5xEAQYASABEgK65PD_BwE

I would estimate that the wires of these clips are about 1 millimeter in diameter. To give you a frame of reference, the alligator clip jumper wires are thinner than the typical wire used to charge a cell phone, but thicker than the extremely tiny low voltage wires that go to residential HVAC thermostats.

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Edit: By the way, my classmates and I use these alliagator clip wires on this practice board to light up light bulbs all the time without any issues due to wire size, so I don't think the wire size is an issue here.

 

[willem2]

Those two legs will have opposite phase. When one is positive, the other is negative. This is done, so you can use 230V equipment between the two legs. (look up split-phase electric power). Connecting them will indeed produce a short.
Does you know circuit theory like ohm's law, Kirchhofs laws, voltage dividers? You want to know about that before tackling anything (sub)atomic.

 

[fourthindiana]

Those two legs will have opposite phase. When one is positive, the other is negative. This is done, so you can use 230V equipment between the two legs. (look up split-phase electric power). Connecting them will indeed produce a short.
Does you know circuit theory like ohm's law, Kirchhofs laws, voltage dividers? You want to know about that before tackling anything (sub)atomic.

I did not know that the two legs have opposite phase.

I know Ohm's Law, but I don't know Kirchhofs Laws or about voltage dividers.

 

[AZFIREBALL]

What is the voltage between L1 and L2:
Are they connected to the mains entering the house?

 

[gneill]

Presuming that the legs will have opposite phase, then the potential difference between them will be 230 V (rms). The wires will have a very small resistance. 1 mm diameter translates to about an 18 gauge (AWG) wire, which has a resistance of about 0.021 Ω/m.

How long were your wires? Guessing that they're a meter or less, an order of magnitude estimate would be that they present about 0.021 Ohms of resistance. Use your Ohm's law to find the current that would occur with 230 V impressed across them. One would assume that your practice board has circuit breakers on the legs that will trip if the current gets too high. Will the current you calculate trip the breakers?

If the breakers were not there, how much power would the wires have to dissipate at that current?

 

[anorlunda]

I know Ohm's Law, but I don't know Kirchhofs Laws or about voltage dividers

Whoa. You need to learn that stuff properly before proceeding. Asking random questions on the internet is a horrible learning method. It is likely to give you spots of knowledge with big gaps. That could make you a dangerous engineer. I recommend a course that includes circuit analysis.

 

[fourthindiana]

What is the voltage between L1 and L2:
Are they connected to the mains entering the house?

The voltage of L1 is 115 volts. The voltage of L2 is 115 Volts. That makes the entire circuit 230 volts.

Yes, leg #1 and leg #2 are connected to the mains entering the house.

 

[sparkie]

When I was in technical school, I actually asked my instructor the exact same thing. He was a chemist by trade, and as such could explain what was happening in the materials themselves, but it just made things worse for me and obfuscated my knowledge. As an HVAC technician, you don't need to know what is going on with anything other than Ohm's law and a basic understanding of electricity. If you ARE more interested in electrical theory, I suggest you get yourself a good self-study theory book. There are a few points I want to drive home to you.

First, don't concern yourself with the "subatmoic level" of what is happening. I started out in tech school (Mechatronics) and even after years in the trade before going to engineering school, I couldn't attain more than just a basic idea of what was going on due to the level of background in the natural sciences. Youtube is a good resource, but I'll give you a rundown. Note that many things have been simplified to give you a very basic intuition that you can begin to build on as you learn and apply in your future career.

Let us look at the requirements for an electric circuit to function. You must have voltage, a resistance, and a complete circuit. Let's examine what happens when you lack one of the three above things. Below, note that I'm only speaking of DC circuits. The subjects I touch on here will give you the intuition to understand what is going on here, but aren't all that accurate of physical descriptions of what is truly happening.

Voltage: If there is no voltage, then there is no transfer of electrons. Let's think about it for a second. So in our theoretical circuit, the negative side has 10* more electrons than our positive side, hence the reason it is the negatively charged** side of the circuit. As the electrons flow, 1 by 1 through our wire, there is energy being used. This "difference of electrons" is often referred to as potential difference. The "potential energy" that exists because the negative side of the battery has 10 more electrons than the positive side. Without this difference in electron density, there would be no electrons flowing (aka current) and no energy would be moving (aka electricity). Note that this difference is between two points. Any two points can and often do have a potential difference between them, though many times it is VERY small.

Complete circuit: This is simple enough. If there is no complete circuit, even with there being a potential difference (voltage) between two points, current would not flow. There would be no transfer of electrons, and therefore no electricity. This is also another reason why electricity is so useful. It can often be quite trivial to simply open up a circuit to shut off lights in a room, or stop a condenser motor.

Resistance: According to Ohm's Law, V = I * R. If we do some algebra on that, we get R = V / I. You have see it in the form of R = E / I . Okay, so what this means is that each one of the quantities affect each other. Simply due to the natural law that the resistance of a circuit is equal to the voltage divided by the current, if the resistance is 0 (as shown in your picture) then we have unpredictable results. Essentially, you can get E / I = 0 by either having no voltage (open circuit) or having I go to infinity (short circuit)***. Either one mathematically gives you R = 0. Now, let's step away from the math and take a look at what having infinite current means.

Having Infinite Current: So, now having an infinite current just means that it starts getting really big and never stops. As you move a lot of electrons through your conductor (wire) they release heat. It is like how electric stove burners or heating elements glow red hot. It releases a large amount of energy all at once. and will blow fuses, trip circuit breakers, and in more unfortunate cases melt components, start fires, and keep you in a steady job.

In your particular situation, you have a potential difference of 240VAC. Basically, with two 120V lines on a typical American single phase (split phase) service, you have +120V and -120V referenced. Each one has 120V to your neutral, but there is a difference between them of 240V (+120 - (-120) = 240 ). I'm not going to get into services and such right now, as it adds a lot of complexity, but I have written about it on these forums before. Just know that you are essential making a circuit with 240V, 0 resistance and infinite current.

I'm also going to give you a couple tips about working on your equipment:

First, start thinking of things as energy transfer. You have heat in air, your air handler transfers electrical energy into mechanical energy via the motor and a fan blade and that energy is then moving air. This air then goes across your evaporator coils, where heat is removed from the air, and carried via your refrigerant outside to your condenser, where once again electrical energy is transferred to mechanical energy, which moves air, which moves heat.

Second, start looking at your circuits in terms of power and control. The power part of the circuit is the part that does what I just described above. It is the part that does things like turn on motors. Then, you have the control side. It will be a lower energy circuit. It uses much less current and almost always a stepped down voltage. This makes it much safer, and it is often the part of the circuit that does the "switching". Making this designation is important for troubleshooting.

Wow, that turned out to be a lot more than I intended, but I really hope it helps!

**This footnote is me telling you a couple random things: First, read up on charge. This will help you out when you start looking at single phase motors. Capacitors are like tanks for charge.
***Short circuits aren't always like this. The short you have described called a "direct short" and on 240V will make a very nice boom. On typical HVAC gear that often has a breaker size of 30A or higher, it can get pretty dicey.

 

[AZFIREBALL]

The voltage of L1 is 115 volts. The voltage of L2 is 115 Volts. That makes the entire circuit 230 volts.

Yes, leg #1 and leg #2 are connected to the mains entering the house.

DO NOT, UNDER ANY CIRCUMSTANCE CONNECT ANY SIZE WIRE ACROSS (BETWEEN) LINE 1 AND LINE 2 WITHOUT A LOAD !
YOU WILL BLOW UP THE PLACE! THINGS WILL MELT. SPARKS WILL FLY! PHOTONS WILL BE RELEASED! MEGA HEAT WILL BE PRODUCED! YOU WILL BE BLINDED, IF NOT WORSE!

 

[jim hardy]

i couldn't have said it better. Nice Job, azfireball !

 

[sparkie]

Ease up a little guys. @fourthindiana is in a classroom environment being supervised by a trained professional. Better for them to do it under supervision with PPE on than on their own. Also, keep that inquisitive nature and that willingness to discover the answers to your questions.

 

[fourthindiana]

Presuming that the legs will have opposite phase, then the potential difference between them will be 230 V (rms). The wires will have a very small resistance. 1 mm diameter translates to about an 18 gauge (AWG) wire, which has a resistance of about 0.021 Ω/m.

The wires are 1 mm diameter at the biggest.

How long were your wires? Guessing that they're a meter or less, an order of magnitude estimate would be that they present about 0.021 Ohms of resistance.

Yes, the wires are a meter or less. We use 18 inch long alligator clip wires. If we clip two alligator wires together, then it is 36 inches (almost one meter). We never have to clip 3 wires together.

Use your Ohm's law to find the current that would occur with 230 V impressed across them. One would assume that your practice board has circuit breakers on the legs that will trip if the current gets too high. Will the current you calculate trip the breakers?

The practice board has fuses, not circuit breakers. I used Ohm's Law on this. 230 volts divided by .021 ohms is 10,952 amps. I'm confident that 10,952 amps is enough current to break the fuses. But why would current flow at all? Would current flow from leg #1 to leg #2 (or vice-versa) because the two legs are out of phase with each other? If so, how could you know which way the electrons travel? Or would the electrons from leg #1 travel to leg #2 simultaneously as electrons would flow from leg #2 to leg #1?

If the breakers were not there, how much power would the wires have to dissipate at that current?

Power = voltage multiplied by amperage

Power= 230 volts multiplied by 10,952 amps= 2,518,960 watts

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So if one uses a wire to connect line 1 to line 2 without any type of load, approximately 2.5 million watts will flow from line 1 to line 2 (or vice-versa)?

 

[fourthindiana]

DO NOT, UNDER ANY CIRCUMSTANCE CONNECT ANY SIZE WIRE ACROSS (BETWEEN) LINE 1 AND LINE 2 WITHOUT A LOAD !
YOU WILL BLOW UP THE PLACE! THINGS WILL MELT. SPARKS WILL FLY! PHOTONS WILL BE RELEASED! MEGA HEAT WILL BE PRODUCED! YOU WILL BE BLINDED, IF NOT WORSE!

I would not connect a wire from line 1 to line 2. I did not know that I would be blinded though.

 

[fourthindiana]

Ease up a little guys. @fourthindiana is in a classroom environment being supervised by a trained professional. Better for them to do it under supervision with PPE on than on their own. Also, keep that inquisitive nature and that willingness to discover the answers to your questions.

Yes, I am working under the supervision of a trained professional. I wire up the practice board while the electricity to the practice board is turned off. My instructor does not turn the power to the practice board on until after my instructor has inspected my wiring.

 

[jim hardy]

Have fun in class @fourthindiana

you will see somebody make sparks and blow fuses.
That's how we learn what not to do .

Learning from other people's mistakes means we don't have to make so many of our own.
Always be thinking "What is going to happen when i ... ? "

and keep one hand in your pocket.

old jim

 

[gneill]

and keep one hand in your pocket.

Yup. It'll save your life!

 

[AZFIREBALL]

fourthindiana: Help us see why it is so important that you understand the process at the sub-atomic level. How will this help you to become a better HVAC tech.?
You say you would never connect a wire across the Mains but, that is exactly what you proposed in your first message in this thread.
Some things need not be understood fully to successfully take advantage of their characteristics.
Take gravity for example. We all use it every day but, we still do not know what causes it!

 

[fourthindiana]

fourthindiana: Help us see why it is so important that you understand the process at the sub-atomic level. How will this help you to become a better HVAC tech.?

Understanding the process at the subatomic level won't help me become a better HVAC tech. It just would satisfy my curiosity.

You say you would never connect a wire across the Mains but, that is exactly what you proposed in your first message in this thread.
Some things need not be understood fully to successfully take advantage of their characteristics.
Take gravity for example. We all use it every day but, we still do not know what causes it!

I never said that I wanted to connect a wire across the mains. What happened is that it occurred to me that I did not understand at the subatomic level why connecting a wire across the mains would produce an electrical malfunction.

By the way, I think I have figured it out now. I now think that connecting a wire across the mains would cause an electrical malfunction because it would cause enormous current flow from one side of the mains to the other, overloading the circuit with electrons.

 

[Elquery]

I now think that connecting a wire across the mains would cause an electrical malfunction because it would cause enormous current flow from one side of the mains to the other, overloading the circuit with electrons

Yes.

But why would current flow at all [when L1 is hooked to L2]? Would current flow from leg #1 to leg #2 (or vice-versa) because the two legs are out of phase with each other? If so, how could you know which way the electrons travel?

If the lines are directly from the power company (not inverted for example), then we are talking about Alternating Current (AC). This current will oscillate at 60hz (in U.S.A). Meaning the current changes direction 60 times a second.

Ohm's law will show you that current will flow: I=V/R
The voltage, created by the power company and stepped down at the building transformer, will cause current to flow inversely to the resistance in the circuit. By connecting the wires directly between legs, as you suggest, the resistance is VERY low (some have suggested 0, but the wires have some) and so massive current will flow. Current will increase until it reaches the maximum based on the ohm's law calculation, or a component fails. Systems are designed so the component that fails is predictable (fuses and circuit breakers) but in their absence, it can be your actual wires that light up hot and fail.

I did not understand at the subatomic level why connecting a wire across the mains would produce an electrical malfunction.

As others have suggested, I would say that before (or at least along side) attempting to understand the 'electrical malfunction' in terms of the subatomic, I would seek out such concepts as Ohm's law, Kirchoffs laws, differences between AC and DC, circuit analysis, and what is 'charge' (which certainly touches on the subatomic).

 

[krater]

Power= 230 volts multiplied by 10,952 amps= 2,518,960 watts

Bingo. Don't forget this little calculation should your career someday lead you behind those six magical screws and into the jumble of a household loadcenter. Don't forget that those possibly unassuming-looking biggest wires could be connected to not much more than a high voltage fuse on the utility's side at the transformer, and that thing is going to let one HELL of a lot of current flow between anything that's bridging the gap between the two lines before it does (IF it does) finally intervene. 10kA+ (or +++ for more massive structures) is not at all out of bounds.

I'm confident that 10,952 amps is enough current to break the fuses.

Might be true, but how long does this take? Any circuit breaking device acts over some definite time period; the effect is not instantaneous. Commonly household AC (alternating current) runs around 50-60 hertz, or cycles per second. How many times before the circuit actually breaks can the electrical potentials, and current flows, reach maximum between the two lines?

PS. Being an HVAC oriented person you would probably understand the concept of, say, a 4000 watt or 4kw electric space heating element. Imagine the experience of close proximity to what amounts to a 2000kw heating element, even for small fractions of a second. Profound to say the least.

 

[jim hardy]

All protective devices have an "interrupting rating"
beyond which the arcing is just too intense for it to quench.

Look at the household breakers in your panel or on a hardware store shelf.
You'll see a number probably 10,000A "sym" meaning symmetrical, ie not DC..
Here's a 30 amp beaker...

If you expect that breaker to protect anything
don't put it in a panel fed by a transformer that's capable of more than 10,000 short circuit amps.

Copper vapor follows the same gas law as dynamite vapor.

Just something to be aware of in your travels.

A tutorial here
http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/solution-center/technical_library/BUS_Ele_Tech_Lib_Circuit_Breakers_Protection.pdf

old jim

 

[jim hardy]

more here

http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/solution-center/technical_library/BUS_Ele_Tech_Lib_Interrupting_Rating.pdf

blew the case apart and charred the wall...

 

[krater]

I have it on authority that some in the industry abhor the phrase "blow the case up" or the like in reference to fuses, breakers, ect. The proper palliative to use is to say that these devices "rapidly disassemble".

 

[jim hardy]

The proper palliative to use is to say that these devices "rapidly disassemble".

indeed.
Usually written in passive voice too, e.g.
"the case was unable to contain the energy and suffered loss of physical integrity "

http://crosstalk.cell.com/blog/what-is-the-passive-voice