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Answers to Readers' Questions on Physical Science:

AC Wiring

The following 38 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• What are the advantages of 220 v over 110?
• Why does an AC fan go in one direction?
• Setting up 220V compressor
• Seeing sparks from the grounded wire
• Appliances ruined when city hit electric line
• Adapter users energy when disconnected
• Have some ideas about electricity
• Wants to wire the 220 V plug in his garage
• Why does a 110V appliance burn out on 220V?
• How far can I run a 220V line without degrading the line?

Next 10

What are the advantages of 220 v over 110?

Question

August 30, 2009

what are the advantages of 220 v over 110? i have 2 air conditioners, both rated 9000 btu, one 110, one 220

- USA

18232

Answer

The equation for electric power is P = VI. Thus, the higher the voltage, the greater the power for a given current. 220 volts can generate 9000 BTU with less current than 110 volts.

See: http://www.school-for-champions.com/science/electrical_power.htm

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Why does an AC fan go in one direction?

Question

September 9, 2007

salam to all.
my question is we say that AC current changes its polarity but when ever we switch on a fan it always move in same direction. wether the hot wire which we get in home always have the same polarity.
If yes why it has same polarity.
Thanks

nadeem - Pakistan

14376

Answer

The way to make an AC electrical motor go in one direction is done by a clever use of what are called slip rings. These rings control the direction of the current, forcing the motor to go in one direction. The same devices are used in AC generators to alternate the current.

See: http://www.school-for-champions.com/science/electgeneration.htm for an illustration of a slip ring.

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Setting up 220V compressor

Question

May 27, 2007

I'm setting up a Curtis Taledo C89 220v 10hp compressor at my home to sand carve etch large glass panels. I have the correct wall switch (magneto) for it but have forgotten how I had it wired from my last location some years ago. I recall having to get a double breaker switch to accommodate 2- 100v swithes to equal 22O. White to the ground metal strip and then each of the other 2 wires to.....? this is where I get lost. The magneto is still hooked up to the compressor, but how do I hook up from the house box to the magneto box. I sort of remember a regular house light switch (for off/on) on the outside wall, too. Appreciate any help. Josh

Josh - USA

13841

Answer

Typically black is hot, white is common and green is ground.

With your configuration, I would either check with an electrician or handyman who is familiar with wiring. It may cost a little bit, but it is better to make sure you get things right.

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Seeing sparks from the grounded wire

Question

May 17, 2007

I recently helped in wiring a very large warehouse. In some parts of this building you could rub the common on somthing grounded and see sparks, small sparks, not the same as if you grounded a 277 wire. what would you speculate caused the "feed-through" I called it, that varied from nothing in places to a shocking experience in others?

Ted - USA

13804

Answer

One problem on that is sometimes found in the buildings and houses that have been rewired is a floating ground. That is a situation where the grounding is improper or nonexistent and the ground has a DC component. Sometimes the DC voltage is small, but in other cases it can be large enough to give a person a shock or damage sensitive equipment.

One reason for this is the practice of grounding wires to a water pipe. With the use of plastic plumbing piping, grounding to a water pipe may result in no ground of all.

Rectifying floating grounds can be a major hassle. At the very least, make sure that your grounds are true grounds.

I hope these ideas help.

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Appliances ruined when city hit electric line

Question

March 11, 2007

They were putting in city water and hit an electrical line at the pole in front of our house.All the lights were super bright(they said 220 volts went thru the house until I turned the breakers 0ff approx 10 min. and still you could here a buzzing until the power company shut it off at the pole 1 hour later)It caused my TV, airconditioner and refrig. to smoke and damaged a lot of other things (garage door opener, computers, phones, etc)
My question is how concerned about the wiring should we be? Our electrician said the wiring could handle that amount of voltage but I want to make sure the house is safe.....and how can they make sure? Thanks Beth

Beth - USA

13349

Answer

I'm surprised that your circuit breakers didn't turn off the electricity automatically. That is what they're supposed to do in the case of an overload.

Since the wires in your home are relatively thick compared to the finer wires in an appliance, they should be able to take a larger load without overheating. If they did get very hot with the 220 V, the insulation on the wire might melt off in some places. But that would probably cause a short and resulte in a break in the current.

I agree with the electrician that your home wiring is probably safe. But still, it is good to keep an eye open for any strange things that may be happening, like the circuit breakers popping open unexpectedly at times.

Hopefully, the city will pay for the damages done to your electrical appliances. That shouldn't be a burden on your insurance policy, but it should be on the city's, since they were negligent or careless.

Best wishes on getting everything replaced and up and running again.

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Adapter users energy when disconnected

Question

March 9, 2007

Is any electrical power being generated (or lost) when an ac adaptor/charger for a cell phone or lap top computer is left plugged in to a wall outlet, but disconnected from the device itself?

Martin - USA

13336

Answer

Most of them are still taking power from the outlet, although a very small amount. You can tell this by leaving a disconnected adapter in the outlet and feeling it. Typically, they feel slightly warm.

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Have some ideas about electricity

Question

February 26, 2007

So i have a bunch of hypothesis @ideas i would like to run by someone who has experience in electricity. so. first can i use the ground to create an electromag fromwiring a solenoid to the ground? second what is the major problem with using a electric motor to gears to an alternater to generate more electricity than it takes to run it? thanks il

- USA

13254

Answer

The ground is usually used to provide a zero point for DC electricity. It is also used in AC electricity, in case there is a DC component. In an automobile, the ground is the chassis of the car. The starter solenoid in a car as one and grounded to the chassis.

The bearings on the electric motor, the gears, and the bearings on the alternator all have friction. That means that you need to import more all electrical energy than you get out by the generator because of the loss to friction. Another factor is that neither the moter motor nor the generator are 100% efficient.

Although this idea will not work, it is good that you are thinking creatively. Keep thinking of new ideas. That's how inventions are made.

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Wants to wire the 220 V plug in his garage

Question

February 12, 2007

I would like to wire a 220 volt plug in my garage for a portable fan heater. Could you please explain exactly what I have to do in the electrical panel and at the plug. I have a little bit of knowledge about this but would like to be certain before I begin. I believe I would need a 220 breaker and the wire I would have to run from the panel to the plug would be a 3 wire. I'm not exactly sure how I run the wires to the 220 breaker inside the panel. The other question I have is once I get the 220 plug wired can I continue on from this plug to add more 110 plugs or would it be better to run a separate line for these plugs?

Eric - Canada

13136

Answer

That is beyond the scope of our information.

Your best bet would be to hire an electrician to do the job. A little bit of knowledge can be dangerous when working with high voltages. Also, you really need to know what you're doing when you get into the electrical panel.

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Why does a 110V appliance burn out on 220V?

Question

September 11, 2006

sir, my question is that power= current times voltage. if we plug an appliance of 110V with a 220V supply it burns. Although we know that appliances with ratig 110V need more current as compared to 220V appliances. can u explain me please. i am confused.

Muhammad - Pakistan

11897

Answer

One factor is that a heavier gauge wire is needed in the 220V system in order to avoid overheating. Usually the wiring used in a 110V appliance is thinner and will overheat when 220V is applied.

For a given wattage or power, the 110V system has a thinner wire with 4 times the resistance than a 220V system. That resistance would overheat when exposed to 220V.

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How far can I run a 220V line without degrading the line?

Question

May 12, 2006

I had a stove in one part of my house that had 220V. I took it out and now I want to put an electric stove about 50 feet away from the first stove and further away from the circuit breaker. I would like to extend the first line I had to the second stove. How far can I run a 220V line without degrading the line?

Lynn - USA

11098

Answer

There should be no problems extending a 220V line in your house. Degradation would be less than 110V, which can extend anywhere in a large house.

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