Electrical 101: What happens when two positive wires touch each other?

My understanding is that if two wires running AC current at 220V touch whilst there is a neutral present, we get 440V on that line i.e. 220+220=440V

But what happens with DC? My understanding is that in such a case, the line voltage would remain at 12V i.e. 12V DC + 12V DC = 12V DC, even if the sources of the power were different

Thoughts?

With AC, you will get a loud bang if two wires from different phases touch. Nothing will happen though if the wires are connected to the same phase.

AC Voltage measurement is done between phase & neutral OR between phases. So you get 220V when you measure voltage between phase & neutral and 440V between two different phases. There is no +ve or -ve in AC supply.

With DC, you will not get any reading if you do not measure between +ve & -ve. However if the voltage sources are different then it depends on how these sources are connected. If DC sources are connected in series, then you get added up voltage (two 1.5V cells make 3V) and if you connect them in parallel, the voltage remains the same but the current is added up.

Voltage is also called "Potential Difference" i.e. the difference in potential between the terminals. It is always measured between two different terminals.

I 100% agree with kuya. Very nicely explained.

Need different phases in AC to make 440. In DC it needs separate electricity source in series or parallel to make any change.

However, my question is what happens if an electric device (let's assume a bulb) has 220v (same or separate phase) on negative and positive? I mean there is no negative wire, both wires are positive. This might also result into 440v but in totally different fashion. What do you think?

^ Can you rephrase your question? I can't follow what you are trying to ask.

It would help if you use the terms phase & neutral for AC & limit -ve/+ve to DC related queries.

i guess he doesnt have a good concept of what is potential difference...

Let me rephrase the question:

Imagine following situation (AC):

1) In normal condition:

+ Light Bulb -

2) This is my question, what will happen if I switch wires as following:

+ Light Bulb +

Legends:

Light Bulb = AC Incandescent light bulb

+ = Live Wire (Phase) (locally called Positive)

- = Return Wire (Neutral) (locally called Negative)

^^

simple nothing will happen cuz the current will not flow

the current always flow from high potential to low

but in ur case the potential is same at both ends thus the current wont bother to pass ......

^^ Ditto. The bulb will remain off.

@kuya

Can you explain why in an AC system, when two different phases touch each other, it would result in a bang? I understand that the concept of sinusodal waves, and the fact that any given moment, the three phases are at different frequencies, but I don't understand why the two touching each other would cause a explosion or spark?

edit: real life example, what happens when two wires (different phases) on the electrical poles collide? Does it send a jolt of high voltage electricity to the (still) connected lines?

^^ The reason is simple and normally referred to as short circuit. Without any load in between, sparks are guaranteed if wires from different sources (phase & neutral OR two different phases) touch.

If there is some kind of a load in between, then the end result will depend on the potential difference between wires (220V for Phase & Neutral and 440V for two phases) and the connected load's voltage handling rating. Usual devices rated for 220V (even a simple bulb) would not be able to handle 440V.

In your real life example, the result is a short circuit that will eventually cause overload on the source transformer (PMT). Usual result is a blown fuse or in worst cases, blown transformer in the area/building substation/pole mounted PMT.

Please note that the three phases are all 50Hz frequency in our case. However they are 120 degrees out of phase with each other.

Link for further reading

bang bang bang bang......

lol

i think if the 220+220 of the same phace are connected nothin will happen but if the phases are different than i think the wire will melt and ull have build yourself a new home cuz ur old one will be in cinders...

60% of this stuff is going my head.

can you guys simplify and explain in layman terms. Like everybody else here would love to explain IT stuff to n00bs.

i need to re-read all my electronics books :}

[quote=", post:, topic:"]

bang bang bang bang…

lol

i think if the 220+220 of the same phace are connected nothin will happen but if the phases are different than i think the wire will melt and ull have build yourself a new home cuz ur old one will be in cinders…

[/quote]

That was that I was asking.