• satyajit rules

MemberMar 12, 2014

## Parallel Connection

Now i just came across a question regarding parallel connection.

In a four branch parallel circuit , 50 A current flows in each branch.what would happen to current in other branches ,when one branch is opened. means is it increases in other branches or decreases or what?

Though this question is simple but fundamentally worth one.. if any one has idea just share..
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Replies
• MemberMar 12, 2014

Nothing happens in other branches as far as the voltage accross those branches remains the same.

Current flowing through a branch is dependent on the resistance in that branch but not the current in other branches. But the total current drawn from the source will decrease if one branch is opened.

This is exactly similar to the household connections. It doesn't really have an effect on other electrical devices in your home when you switch off or on another device connected in parallel. Switching off a ceiling fan doesn't make the light circuit consume more current.
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• MemberMar 12, 2014

thanks #-Link-Snipped-# .. for the answer.. but one more doubt related to your answer..when we switch on motor/geyser/iron..why there is a change in luminosity of light or tv..etc
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• MemberMar 12, 2014

Current reduces in each branch to 37.5A.
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• MemberMar 13, 2014

Anand Tamariya
Current reduces in each branch to 37.5A.
The current would simply stay the same in all other branches as far as the voltage across them are constant.

Say two 60W bulbs are connected in parallel. If the supply is 230V, both the lamps will consume 0.26A. So if one lamp is switched off, will there be a change in the current that flows through the other branch? No.
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• MemberMar 13, 2014

satyajit rules
thanks #-Link-Snipped-# .. for the answer.. but one more doubt related to your answer..when we switch on motor/geyser/iron..why there is a change in luminosity of light or tv..etc
The appliances you mentioned are high powerd devices. They consume quite a large amount of power and hence current. Enough current is consumed to cause a slight voltage drop in the total circuit. This voltage drop will be easily reflected in other devices like light sources causing a slight dimming.

The issue can be avoided to a great extent if a special circuit with the right sized wires are provided exclusively for high power applications. Aged circuits and loose connections are another culprits. Besides, if the power distributer is not capable to supply the load, a drop will occur no matter how good the wiring is.
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• MemberMar 13, 2014

lal
The current would simply stay the same in all other branches as far as the voltage across them are constant.

Say two 60W bulbs are connected in parallel. If the supply is 230V, both the lamps will consume 0.26A. So if one lamp is switched off, will there be a change in the current that flows through the other branch? No.
Resistance in parallel is:
1/R = 1/R1 + 1/R2 + ....
and V = IR.
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• MemberMar 13, 2014

If the four branches are connected across a constant voltage source, they will always draw 50A each no matter how many else of them are open.

Say the resistance of each branch is R ohms.
When all branches are closed,
Equivalent resistance = R/4.
Total current drawn = 50Ax4 = 200A (each branch draws 50A)
Now to find the voltage across the resistances,
Source voltage = I x R = 200 x R/4 = 50R volts.

Let one branch be open.
Still, Voltage of the source is 50R.
Effective resistance = R/3.
Total current drawn = 50R/(R/3)= 150A
Current through each branch = 150A/3 = 50A
(Even easier if you say, current = Voltage across a branch /R = 50R/R = 50A)
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• MemberMar 13, 2014

lal
If the four branches are connected across a constant voltage source, they will always draw 50A each no matter how many else of them are open.

Say the resistance of each branch is R ohms.
When all branches are closed,
Equivalent resistance = R/4.
Total current drawn = 50Ax4 = 200A (each branch draws 50A)
Now to find the voltage across the resistances,
Source voltage = I x R = 200 x R/4 = 50R volts.

Let one branch be open.
Still, Voltage of the source is 50R.
Effective resistance = R/3.
Total current drawn = 50R/(R/3)= 150A
Current through each branch = 150A/3 = 50A
(Even easier if you say, current = Voltage across a branch /R = 50R/R = 50A)
I stand corrected.
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• MemberMar 13, 2014

In my own piont of view in respect to your very first questn, other branches closed current wil increase.
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• MemberMar 13, 2014

#-Link-Snipped-#. Remember! In parallel circuit, load share current, while in series they share voltage. From that, did u apply this rule/law in your calculation. If yes! Am yet to be conviced with your explanation. Bcos, the question is on PARALLEL circuit. Thanks
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• MemberMar 13, 2014

ogundele kehinde samuel
In my own piont of view in respect to your very first questn, other branches closed current wil increase.
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• MemberMar 13, 2014

#-Link-Snipped-#, u disagree with my answer. So, explain tinz 2 me den. Thanks.
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• MemberMar 14, 2014

Hi, sorry that I didn't explain. I thought I had written enough to clear it already.

In parallel circuit, load share current, while in series they share voltage.
Yeah that is right. Loads share current in parallel. But which current? The current supplied by the source is being shared.

But how much current does a load consume? That is dependent on the impedance/resistance of the load at a specific voltage. If the voltage doesn't change, no matter how many loads you connect in parallel, a load will consume only the current that needs. If we add more loads in parallel, that would stress the source, but not the other loads in parallel as far as the voltage of the source is constant.

Say you have a 5 ohms resistance connected across a 10V batter.
Current through the branch = 10/5 = 2A

Now add another 5 ohms in parallel.
The voltage across both the resistances are 10V itself, right?
So both will consume 2A each. But now, the load will have to supply 4A in total to supply the needs of both loads. If we remove a load, again the voltage is 10V, and current to be supplied by the load reduces to 2A.

We can add as many branches in parallel till the total current supplied by the load increases to its rated value. It wouldn't affect other loads.
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• MemberMar 17, 2014

lal
The appliances you mentioned are high powerd devices. They consume quite a large amount of power and hence current. Enough current is consumed to cause a slight voltage drop in the total circuit. This voltage drop will be easily reflected in other devices like light sources causing a slight dimming.

The issue can be avoided to a great extent if a special circuit with the right sized wires are provided exclusively for high power applications. Aged circuits and loose connections are another culprits. Besides, if the power distributer is not capable to supply the load, a drop will occur no matter how good the wiring is.
but the connection is in parallel na.. why a voltage sag will be there.. does parallel connection assume no voltage sag only theoretically..in real there is voltge sag..?
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• MemberMar 17, 2014

lal
Hi, sorry that I didn't explain. I thought I had written enough to clear it already.

Yeah that is right. Loads share current in parallel. But which current? The current supplied by the source is being shared.

But how much current does a load consume? That is dependent on the impedance/resistance of the load at a specific voltage. If the voltage doesn't change, no matter how many loads you connect in parallel, a load will consume only the current that needs. If we add more loads in parallel, that would stress the source, but not the other loads in parallel as far as the voltage of the source is constant.

Say you have a 5 ohms resistance connected across a 10V batter.
Current through the branch = 10/5 = 2A

Now add another 5 ohms in parallel.
The voltage across both the resistances are 10V itself, right?
So both will consume 2A each. But now, the load will have to supply 4A in total to supply the needs of both loads. If we remove a load, again the voltage is 10V, and current to be supplied by the load reduces to 2A.

We can add as many branches in parallel till the total current supplied by the load increases to its rated value. It wouldn't affect other loads.
but the power of the source increases by each time when we going on adding resistors in parallel .. if the supply is a constant power source..that generally occurs.. what will happen to source?
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• MemberMar 18, 2014

satyajit rules
but the connection is in parallel na.. why a voltage sag will be there.. does parallel connection assume no voltage sag only theoretically..in real there is voltge sag..?
Every conductor has a resistance. This resistance causes a voltage drop. And, the resistance is dependent on its length and cross section. The voltage drop is negligible as far as the current through it is small. But, once the current increases, this voltage drop increases. With higher currents it becomes noticeable. That is when you see the lights dimming.
but the power of the source increases by each
time when we going on adding resistors in
parallel .. if the supply is a constant power
source..that generally occurs.. what will happen
to source?
The load on supply increases as resistors are kept on adding. But, no source is an infinite supplier of power. Yes, it would trip when the current to be delivered overshoots its maximum capacity. Voltage will remain constant across the source till this maximum capacity theoretically.
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• MemberMar 18, 2014

lal
Every conductor has a resistance. This resistance causes a voltage drop. And, the resistance is dependent on its length and cross section. The voltage drop is negligible as far as the current through it is small. But, once the current increases, this voltage drop increases. With higher currents it becomes noticeable. That is when you see the lights dimming.

The load on supply increases as resistors are kept on adding. But, no source is an infinite supplier of power. Yes, it would trip when the current to be delivered overshoots its maximum capacity. Voltage will remain constant across the source till this maximum capacity theoretically.
lal
Every conductor has a resistance. This resistance causes a voltage drop. And, the resistance is dependent on its length and cross section. The voltage drop is negligible as far as the current through it is small. But, once the current increases, this voltage drop increases. With higher currents it becomes noticeable. That is when you see the lights dimming.

The load on supply increases as resistors are kept on adding. But, no source is an infinite supplier of power. Yes, it would trip when the current to be delivered overshoots its maximum capacity. Voltage will remain constant across the source till this maximum capacity theoretically.
so you say that to maintain the rate power of an equipment(may be light,tv etc) as the current increases,voltage decreases..that causes diming.. so dimming is only due to result of voltage sagging not due to current..
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• MemberMar 19, 2014

Why voltage decreases? Isn't it because of the high current flow in this case? Wasn't that we were talking about in all these posts? There are many more reasons that might cause a voltage sag. I suggest you refer the text books and use the vast internet a little.
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• MemberMar 19, 2014

lal
Why voltage decreases? Isn't it because of the high current flow in this case? Wasn't that we were talking about in all these posts? There are many more reasons that might cause a voltage sag. I suggest you refer the text books and use the vast internet a little.
can u refer me some books related to practical applications..
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• MemberMar 20, 2014

Every text book has information. There is no such thing called an ideal text book. If one book can't explain certain things clearly, refer some other books for those foggy parts.
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