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rojo's avatar

If I have a 110v outlet and plug in a power strip with five sockets, why do I get 110v out of each instead of 22v?

Asked by rojo (15989 points ) August 23rd, 2014

Or for that matter, why do I get 110v out of each outlet socket on a standard duplex outlet instead of 55v?

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31 Answers

whitenoise's avatar

Because of the type of circuit used.

This is called a parallel circuit.

Compare voltage to water pressure.

If you would poke multiple holes at the same height from the bottom of a bucket full of water, then all holes would remain to have the same water pressure.

The pressure only changes when the overall water level of the bucket drops. If the bucket is big enough and as long as there isn’t too much water flowing, the pressure at each hole stays the same, independent from other holes you’d poke in the bucket.

LuckyGuy's avatar

Let’s do a thought experiment. (Don’t actually do this with real electricity!)
Let’s start with an outlet with only one socket that has a smaller blade hole and a large blade hole. Stick a volt meter in there and you will get 110V between the small blade and the large blade. Agreed?
Now let’s stick a 3ft long black wire into the small hole and a 3ft long white wire into the large blade hole. Measure the voltage at the end away from the outlet. What do you get? 110 V. Agreed?
Now let’s stretch the 3 ft wires out into 2 parallel lines about an inch apart so they look nice and neat. The black and white wires are not touching each other. Got it?
Now I will give you a socket that has 2 screws for attaching wires a sliver one and a brass one. The brass one is connected to the small blade hole and the sliver one is connected to the large blade hole. Hook up the free end of the black wire to the brass screw.and hook the free end of the white wire to the silver screw. Measure the voltage at the new socket and you will see 110V. Right?
Hey. That worked so well let’s add another socket in the middle. Scrape the insulation away and hook up another socket. Measure it. Yep. Still 110V.
Add another, and another. They are all going to read 110V.
You are hooking up the outlets and sockets in Parallel.

ARE_you_kidding_me's avatar

It’s a parallel circuit.

Dutchess_III's avatar

Running to ask my husband…...

Dutchess_III's avatar

Ok, Rick says it’s because it’s a series circuit, or continuous circuit. He doesn’t think it’s a parallel circuit.

Dutchess_III's avatar

I just electrocuted myself with @LuckyGuy‘s experiment.

Dutchess_III's avatar

OK, he’s drawing a diagram.

Dutchess_III's avatar

Ok… the longer the wire, the less amps you can get through that wire.
ME “What’s the difference between amps and voltage?”
Rick “Amps will kill you, voltage will sting you.”

Here is what his diagram looks like:
__________________________________________

X…............. X….............. X ..................... X…............. X
__________________________________________

He says “parallel” means they’re running NEXT to each other. Your power strip is a continuous circuit. You can’t lose voltage because it is what it is, but you can lose amps.

I have no idea what he’s talking about.

whitenoise's avatar

@Dutchess_III

I hope Rick makes his living in another way than as an electrician. :-)

whitenoise's avatar

Two lamps set in series will share the same current, but will divide the available voltage, based on their resistance.

Two lamps set in a parallel circuit will share the same voltage, but divide the current.

Either way each lamp will experience a voltage that equals their resistance times the current running through them.

Hope I haven’t lost anyone.

Dutchess_III's avatar

No, he’s not an electrician, but he does electrician stuff. And plumbing stuff. And all kinds of stuff.

But it IS a series of outlets, right? Or…what does the inside of a power strip look like?

whitenoise's avatar

When in series, it is like connecting two hoses in line. Each will transport the same amount of water (the current) the pressure in the narrow hose would be higher than in the wider hose (the voltage), though.

Now when two hoses are running parralel (and there is enough water) then each will get the same water pressure (voltage) but the wider hose carries more water (current). This would be like having two taps next to each other on one pipe.

Either way the water supply must be adequate. (The wall socket must have an adequate power rating.)

Dutchess_III's avatar

Um looking for what the inside of a power strip looks like….

whitenoise's avatar

From Wikipedia:

If two or more components are connected in parallel they have the same potential difference (voltage) across their ends. The potential differences across the components are the same in magnitude, and they also have identical polarities. The same voltage is applicable to all circuit components connected in parallel. The total current is the sum of the currents through the individual components, in accordance with Kirchhoff’s current law.
(http://en.m.wikipedia.org/wiki/Series_and_parallel_circuits)

Dutchess_III's avatar

OK, I’m being simple, I’m sure, but I don’t see any thing “parallel” in this. Parallel means to run side by side. What I see here looks more like “continuous,” or a “series.”
So what am I missing?

whitenoise's avatar

In your picture, you can even observe two long copper plates physically being parallel.

Dutchess_III's avatar

Ok, yeah. I see it. I think I’m starting to understand. When you plug into an outlet, the metal plugs are each attached to their own wire, not the same wire, right?

ARE_you_kidding_me's avatar

I’m willing to stake my electrical engineering degree on the fact that the outlets are in parallel and not series.

jerv's avatar

As others have stated, it’s a parallel circuit. No matter which of the five outlets on the strip you use, they all share the same end points. The voltage drop between those points is the same no matter which path the electricity flows. While a diagram may show parallel lines, as far as the electricity is concerned, it’s all just one single point.

As I can’t post pictures from my phone very easily, the best visual I can give is this; take 5 twist-ties, put them together, and then just twist only the ends. You’ll have 5 middles, but only 2 ends. Five lines that are electrically parallel regardless of their physical shape. Five lines with common ends, and you’ll get 110v no matter which line you choose.

In a series circuit, the voltage across each load would vary based in it’s resistance; it wouldn’t necessarily be 22v across each load unless all five loads had equal resistance.

rojo's avatar

Thanks for the information. I am understanding the concept but still not completely clear. If I have several outlets in a row run in parallel, then each outlet draws from its own separate power source thus no drop in voltage but if they are run in series then each time I plug in an appliance would I decrease the voltage on the next outlet until I eventually ran out of volts?

ARE_you_kidding_me's avatar

A series connection will obey ohms law: Voltage =current x resistance. The more resistances are added the lower the total current will be. Each series load will divide the voltage accordingly. Each series component has the same current but a different voltage (unless the loads are the same) Each parallel resistance will have the same voltage but different current (again unless the loads are the same) That’s the basic theory. With AC things do get more complicated but it’s valid for our discussion.

jerv's avatar

In parallel, they all draw from effectively the same source. Each gets the same voltage.

In series, each load gets what’s left over after the load(s) before it takes some voltage away; none will get full voltage.

rojo's avatar

So, are wall outlets run in series? Is that why they limit the number of outlets/switches that can be on the same breaker?

ARE_you_kidding_me's avatar

Parallel, the limit is on current capacity

jerv's avatar

When loads are in parallel, adding more loads reduces the total resistance of the circuit as electricity has more ways to get from points A to point B. Ohm’s Law dictates that I = E / R, so as resistance drops, amperage (current) rises. If it rises too high, the wiring will heat up enough to catch your house on fire. Breakers keep it from getting that high.

rojo's avatar

@ARE_you_kidding_me thank you for the graphic but from my way of looking at it outlets are in series. A single wire goes from one to the other and so on until the last in the line. Is that not correct?

whitenoise's avatar

@rojo

In the old days we had Christmas light strings that were setup in a series configuration.

Remember hunting for the broken bulb and switching it on and off by twisting one of them?

(And keeping the location of that one a secret to the rest of the family?)

jerv's avatar

@rojo There’s a difference between a straight line and a T. You’re seeing one wire, but the electricity sees multiple Tees. It forks off on multiple paths.

whitenoise's avatar

Outlets are in parallel.

The single wire (cable) you mention contains actually two wires, one phase and one neutral.

In the box at the end of the cable, where the outlets are, these wires will be connected to two metal strips.

One of these strips will be the base for all the phase connectors of the box’s outlets.

The other strip will be the base for all the neutral connectors of the box’s outlets..

Sometimes there will be a third wire in the cable and a third strip in the box for ground.

ARE_you_kidding_me's avatar

This page
Shows multiple outlets wired in parallel. Earth ground is usually green in modern houses.

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