Efficiency or energy savings of 240 Volt vs 120 Volt appliances & devices:

This article describes the difference between wiring an electrical motor, such as a well pump, to operate at 120 volts compared with 240 Volts and answers the common question of whether or not wiring an electrical device to operate at higher 240 Voltage level will save on the electrical bill by using less energy.

The short answer is no, and details are provided below. Sketch courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ]. Photographs and sketches illustrate voltage, electrical resistance, and other electrical wiring concepts.

Does Wiring a Motor at 240V Save Electricity over Wiring it to Run at 120V?

As we discuss at both

AMPS VOLTS DETERMINATION and

at VOLTAGE at the SEC the total current (Amps) that will flow through a wire (electrical conductor) is cut in half if the pressure (Volts) is doubled.

Twice the electrical power or energy (or more-accurately in Watts) can be delivered on a # 12 wire by doubling the voltage and holding the current unchanged, for example at 20 amps.

Doubling both voltage and also doubling the amperage would deliver four times the power or energy. Thanks to reader Bob Hawley, for careful reading & editing of this point.

But doubling the power or energy (expressed more-accurately current measured in amps - or as most readers prefer, Watts) does not mean that we cut our electrical bill in half.

Why not?

Our photo atbove shows a 240V pump control switch. [Click to enlarge any image]

As we introduced at DEFINITION of VOLTS, Volt, formally, is defined as the potential difference across a conductor when a current of one ampere dissipates one watt of power.

This definition is not very helpful to consumers. Using a water-in-pipes analogy, volts is analogous to water "pressure" in the electrical system.

Having higher "pressure" in a pipe (or electrical conductor) means that conductor is capable of delivering more energy to the user.

In our article on electrical definitions we

explain ELECTRICAL POTENTIAL.

Mathematically the following simplified formula relates volts, watts, and amps in an electrical circuit

Volts = Watts / Amps.

To see definitions of each of these terms use the live links below.

VOLTS [Definition] equals WATTS [Definition] edivided by AMPS [Definition].

Electrical Energy Usage Measured in Watts

The watts consumed (and therefore the size of your electric bill) for running a water pump or other electric motors will be almost exactly the same regardless of whether you are running the pump wired at 120 Volts or 240Volts.

Using an imperfect "water pressure" analogy, sending water through a pipe to move a water wheel, if we double the pressure (volts) at which we are supplying water energy to push the wheel, the number of gallons per minute (amps) we need to do the same work is cut in half.

So if we keep our pipe and water wheel and all else the same, but send water through the pipe to push the wheel at 240 psi, we would need half as much water quantity (measured in gallons per minute or "amps") to turn the wheel at the same rate as if we were pushing on the wheel at 120 psi.

[Click to enlarge any image]

Electrical motor voltages 

are similar in this regard. If we have an electric motor that is designed to run at either 120V or 240V (not all of them are) then the label on the motor will tell us that at 120V (pressure or potential) the pump motor will draw about twice as much amperage (current) as at 240V.

Our label (photo at left) shows that this 1/2 horsepower jet pump electric motor can run at either 115V at 10.8 Amps of current draw, or at 230V at 5.4 Amps of current draw.

With this example, if our electric pump motor draws 10.8 Amps when running on a 120V circuit, you see from the motor label that it draws 5.4 Amps when in use on a 240CV circuit.

10.8 Amps = ?Watts / 120 or doing the algebra, 120 x 10.8 = 1296 Watts when our pump motor is running at full load and wired on a 120 Volt electrical circuit.

05.4 Amps = ? Watts / 240 or doing the algebra: 240 x 5.4 = 1296 Watts when our pump motor is running at full load wired on a (nominal) 240 Volt electrical circuit.

The electric meter at a building measures electricity usage in kilowatt hours (KWH). If you run a 1000W electric heater for one hour, you've just used 1 KWH of electricity. So the pump is costing essentially exactly the same to run at either voltage level.

So what advantages do we get from running an electric motor at 240V rather than 120V?

Most electric motors will be a little easier to start turning at higher voltage. And for the same amperage draw, at 240V a smaller diameter circuit wire may be permitted - thus the circuit is a little less costly.

Finally, on a long circuit, the voltage drop due to resistance of the wire itself will be less at 240V than at 120V. However, separately, some experts point out that higher voltage circuits are potentially more dangerous.

In sum, the electric bill is about the same, but at 240V the pump has a little easier time starting, it may thus have a little longer life, and the wiring might be less costly.

The improvements in efficiency of use of electrical power is slightly better at higher voltages (less energy loss) but running a water pump will not be noticeably more or less costly between the two options.

See DEFINITIONS of ELECTRICAL TERMS for definitions of Amps, Volts, Watts, Ohms, etc.

Our photo at left shows the data tag inside of a pump pressure control switch and shows that the switch might be wired for either 120V or 240V if other site conditions and equipment specifications permit.

Reader comment: 220/240 50/60HZ Motors last longer

(Oct 29, 2015) RB Davis said:

The reason for using 220/240 50/60HZ is that Motors last longer. It's a well known fact it is more economical to use that rather that household current.

Ask yourself why Industry does not use 120VAC motors in HD applications?

And we all know HD products are better than household products.

Certain facts come from hands on experience and general wisdom that age and experience provides, Not all things are "by the book" or apparent by simple math equations. - RB DAVIS - Electro-Mechanical Eng., formally with Struther-Dunn Relays.

Reader comment: Todd says that 220/240 VAC electrical systems are safer

OPINION: a 220v system should be safer then a 120v system. [Editors note: Watch out: this claim is incorrect and may be unsafe]

The amps is what is the most dangerous in any system. The higher amps is what kills you not the voltage. Since a 220v system uses half the amps allowing you to use smaller wiring this also makes it twice as safer then a 120v system since the ps needed are reduced by half. In reality not only is the 220v system cheaper because of lower amp use it and wiring costs it also is safer for your health. This is why most countries have swapped to 220 systems.

OPINION: The claim that swapping over from a 120v to a 220v system is to costly is a gigantic lie told by power companies and electronics manufacturers to keep their profits up by selling over worked products and constant repairs. If we swapped over to a 220v system which is proven more safe and effective as well as a lot lower cost to creat and maintain our electric devices would last a lot longer as they would be working half as hard. This is why more and more buildings in the US are being built using a 220v system instead of a 120v .So in reality the 220v system is the smartest thing anyone could do for their home. - Todd P. 2023/01/02

Moderator reply: Not exactly right: electrical safety, shock & fire hazards are a bit more complex than explained by voltage alone

Thank you so much for commenting. We agree that when someone is being shocked, amps or level of current is an important factor.

But you're not quite right to say that 240V is safer than 120V. Doubling the voltage, if all else is unchanged, will double the current flow.

The human body is resistant to the flow of elecricity - varying depending on body part and surface moisture. Some sources put the electrical resistance of a dry hand at over 100,000 Ω ohms while the internal resistance of a human body is around 300 Ω. (We're mostly salty water).

If you (DO NOT DO THIS - IT WILL KILL YOU) grabbed one end of a live 240V wire with your left hand and the other end of that cut wire with your right hand, current would flow through your hands and arms and body, across the heart (you will be dead in an instant) - those electrons being "pushed" harder through your body by 240V than say 120V, or for an easier example a 12-volt circuit. (Most people could touch 12-volts without serious injury).

So being shocked by 240V is more dangerous than being shocked by 120V. The 120V circuit is actually less likely to kill you.

Current (amps) alone isn't the whole story when understanding electrical shock hazards.

When a person is exposed to electric shock, a higher current may, with all other factors being equal, produce a higher current through the person's body. Remember that layperson's explanation that we can think of volts as "pressure" and (as I often put it), amps or current as "effective total flow rate - or if it were water, gallons per minute".

Put another way, if all other factors remain unchanged, an increase in voltage will produce an increase in current or electron "flow" through a conductor.

As you'll read in the research below, both electrical shock hazards and electrical fire hazards are more complex than simply comparing the two voltages 120VAC and 240VAC that you cite. (Shea 2008)

Bernstein (1991) points out that

The voltage in a circuit is only important insofar as it will produce a given current depending on the impedance in the circuit path.

Higher voltages can cause serious burn injury because of the heat of the arc and the tissue damage caused by large currentys. The higher currents associated with high voltage shocks tend to p;roduce cardiac asystole rather than ventricular fibrillation [7], [8].

Death at lower voltages, such as 120 / 240V, can usually be attributed to ventricular fibrillation. Depending on the type of electrical contact made and the current level produced by the voltage, death can occur at these voltages with no electrical burn marks on the body and with no definitive autopsy findings that could prove electrouction had been the cause of death. (Bernstein 1991).

That's why GFCI devices are designed to sense and trip "off" at very low current leakage levels. As we explain

at GFCI PROTECTION, GFCI CODES, just 5 mA (0.005 Amps) of current leakage from hot to ground will trip a Ground Fault Circuit Interrupter device.

I'm not sure where you think we've said anything to the contrary.

I'd be grateful if you can suggest a few authoritative citations so that we can add that to the explanation of comparative safety of 220V vs 120V electrical systems & the "amps" risk. We include some of our own research on the comparative safety of 120V vs 240V electrical systems just below.

• Bernstein, Theodore. ELECTRICAL SHOCK HAZARDS AND SAFETY STANDARDS [PDF] IEEE Transactions on Education 34, no. 3 (1991): 216-222.
• Bernstein, Theodore. "Electrocution and fires involving 120/240-V appliances." IEEE Transactions on Industry Applications 2 (1983): 155-159.
  Abstract:
  
  The most serious accidents with 120/240-V appliances are probably those involving electric shock and fire. To aid in the investigation of such incidents, some fundamental concepts are presented for the accident investigator.
  
  For electric shock cases a knowledge of the effects of electricity on the human body and the electrical parameters related to these effects is important. Since most shock cases involve a question as to the path of current to ground or whether the grounding was proper, present day grounding procedures are described for appliances.
  
  To aid in investigations of accidents involving older equipment or systems, a history of the National Electrical Code's (NEC) grounding requirements and allowable use of double insulation for cord- and plug-connected equipment is included.
  
  In the investigation of fires of possible electrical origin, the investigator is usually confronted with arc damage that either caused the fire or was caused by the fire. A discussion of the fundamentals of electric arcs and of circuit protection is presented to aid in this determination.
• Bridges, Jack E., G. L. Ford, and I. A. Sherman, eds. Electrical shock safety criteria: Proceedings of the first international symposium on electrical shock safety criteria. Elsevier, 2015.
• Bridges, J. E. "An investigation on low-impedance low-voltage shocks." IEEE Transactions on Power Apparatus and Systems 4 (1981): 1529-1537.
• Gardner, John, and Joe Alanis. "A comparison of international wiring and grounding systems with North American methods." In 2008 55th IEEE Petroleum and Chemical Industry Technical Conference, pp. 1-7. IEEE, 2008.
• Li, Lulu, Jing Yong, Liqiang Zeng, and Xiaoyu Wang. "Investigation on the system grounding types for low voltage direct current systems." In 2013 IEEE Electrical Power & Energy Conference, pp. 1-5. IEEE, 2013.
• Reynolds, Terry S., and Theodore Bernstein. "The damnable alternating current." Proceedings of the IEEE 64, no. 9 (1976): 1339-1343.
  Abstract:
  While the struggle over the use of alternating cunent (AC) versus direct current (DC) in the United States lasted from 1886 to 1895, the critical year was 1888.
  
  Early in 1888 the Edison DC interests first launched public attacks on the technical aspects of C. Later they redirected the controversy, from a general consideration of comparative merits, to concentrate on only the safety issue.
  
  The decision of dc interests to launch public attacks on ac was probably caused by the success of a French copper syndicate in cornering much of the world's copper supply and forcing prices sharply upward in 1887. This made the lower copper costs of ac systems an attractive selling point and forced dc proponents to react.
  
  Thus the early months of 1888 saw a number of well-rounded discussions on the comparative merits of the two systems. The decision in mid-1888 to focus the debate on the safety issue was related to the discovery, in the spring of that year, of a workable principle for an ac ampere-hour meter (Shallenberger) and an ac motor (Tesla).
  
  The Edison interests were largely successful in focusing the polemics on the safety issue and achieved several major publicity coups (such as the use of ac for the first legal electrocution), but they were unable to match the technical improvements that by 1895 were clearly to make ac a far better system of power transmission.
• Shea, John J. "Comparing 240 Vrms to 120 Vrms series arcing faults in residential wire." In 2008 Proceedings of the 54th IEEE Holm Conference on Electrical Contacts, pp. 218-224. IEEE, 2008.
  Abstract:
  A comparison of the two system voltages, nominally 120 V _rms and 240 V _rms  at 60 Hz, typical of North American residential applications, was made to determine why a series arcing fault in SPT-2 wire at a 240 V _rms had a significantly higher probability of fire ignition than at 120Vr_rms  even though the arc voltages were similar for both system voltages.
  
  Experiments using SPT-2 wire were performed per UL1699 standards at each voltage level with equal nominal steady-state non-arcing load currents (e.g. 5 A rms , 10 A rms , 15 A rms , 20 A rms and 30 A rms )- It was shown that the arc power, dissipated in the series arc, was greater at 240 V_rms  than 120 V_rms due to increased arcing current.
  
  This was attributed to the arcing path resistance being a larger percentage of the total circuit resistance, reducing arcing current at 120 V_rms , and also to an increase in the number of arcing half-cycles at 240 V rms because the higher system voltage was more likely to breakdown the gap than at 120 V rms .
  
  Both these factors combined created a higher average arcing current at 240 V _rms  .
  
  Furthermore, the increased arc power would result in a hotter carbonized contact gap - further reducing the breakdown strength of the gap. The average arc voltage however remained about equal for both voltage levels. These results may be useful for exploring additions to the UL1699 "fire curve" for 240 V_rms  applications.

Don't Rush to Re-Wire your Well Pump from 120V to Change it to 240V

The pump pressure control switch in our photo at left has contacts that permit it to be wired to operate at either 120V or 240V.

But we don't know if the pump motor itself can run at either voltage.

First make sure that the pump motor and control are labeled to indicate that either voltage level is permitted with the equipment you have installed.

Second we don't know that the pump motor, even if it can run at 240V, will not also require a heavier-duty pump control switch than this relay.

Second, there will be some additional costs when changing the voltage level at which an electric motor is going to be operated.

Even if the electrical wires can be left un-changed (when moving UP from 120V to 240V) the overcurrent protection (circuit breaker or fuses) will need to be changed to properly and safely protect the electrical circuit.

In either case, if we exceed the current rating of an electrical wire, it will get hot, risking a fire. That's why we use fuse devices (or modern circuit breakers), to limit the current flow (amps) on electrical conductors to a safe level to avoid overheating and fires.

Some but possibly not all motor controls such as well pump control switches can be re-wired to operate at either voltage. But if not you'll need to replace the pump control switch.

The wall switch to turn off the well pump will need to be changed and rewired if you change the voltage serving the pump.

So when might we make these changes? Certainly when a new well pump is being installed or when other electrical work is being done on a building that would be the time to ask your licensed electrician about pump wiring and circuit voltage.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2023-01-02 by (mod)

Please find your comment and our detailed reply in the body of the article above.

Watch out: some of what Todd says below is mistaken and dangerous - Ed.

On 2023-01-02 by Todd P

220v system should be safer then a 120v system not the other way around blike you claim. The amps is what is the most dangerous in any system. The higher amps is what kills you not the voltage. Since a 220v system uses half the amps allowing you to use smaller wiring this also makes it twice as safer then a 120v system since the ps needed are reduced by half. In reality not only is the 220v system cheaper because of lower amp use it and wiring costs it also is safer for your health. This is why most countries have swapped to 220 systems. The claim that swapping over from a 120v to a 220v system is to costly is a gigantic lie told by power companies and electronics manufacturers to keep their profits up by selling over worked products and constant repairs. If we swapped over to a 220v system which is proven more safe and effective as well as a lot lower cost to creat and maintain our electric devices would last a lot longer as they would be working half as hard. This is why more and more buildings in the US are being built using a 220v system instead of a 120v .So in reality the 220v system is the smartest thing anyone could do for their home.

Also those with a 220v/240 system can always use a plug in step down transformer at any power outlet to reduce the voltage to 110/120v for other appliances reducing any need for extra breakers for 110/120 appliances.

On 2021-09-16 by inspectapedia.com.moderator (mod)

@Hairydog42,

For other readers: keep in mind, however, that the COST of electricity you use will in most cases be absolutely the same, regardless of whether you are running a device at 120VAC or 240VAC.

Most electricians will simply say "220v power is more efficient in terms of current because it requires less to provide the same power due to the increased voltage. As mentioned previously, however, this increase also means 220v poses a higher safety risk than 110v."

But in countries where common branch circuits are 120V using 220V isn't an option for those individual circuits, while other circuits such as those supplying an electric clothes dryer or cooktop are already requiring and wired for 220V.

On 2021-09-16 by Hairydog42

this comment is also related to why load balancing is important.

On 2021-09-16 by inspectapedia.com.moderator (mod)

@Anonymous,

Good points and for the case you describe I agree completely.

Thank you.

You can see from my earlier response that we keep in mind that we have readers in over fifty countries using a variety of electrical service types and with skill and training ranging from expert to novice;

so we need to keep that in mind to reduce the chances of getting someone in trouble.

On 2021-09-16 y Anonymous

@inspectapedia.com.moderator, I am familiar with US. What you mention is true if you are wiring devices that are only designed for 120. There are many situations where you do have a choice 120 vs 240. Example, you are adding a number of electric space heaters. Do you choose to purchase and install 120v devices or 240 v? Some can be wired either way. These types of devices usually need to be on a dedicated circuit. If you don't have a shortage of available slots in the panel you'll come through, or your adding a panel for the upgrade, you should choose 240 for these kind of units. If you have large loads that can come on independently, you can naver really balance the 2 legs just by putting a similar count/size of 120 on each leg in the panel because the devices can come on at independent times. But if the bulk of your large loads are pulling across 240, it doesn't matter which ones are on. the bulk of your overall load will tend to be balanced.

On 2021-09-16 by inspectapedia.com.moderator (mod)

@Hairydog42,

Thanks that's an interesting idea.

Keep in mind that balancing load across the two legs of the 240V service is best achieved by taking care to mount an equal number of 120V breakers on each side or each leg in the panel, AND in mounting breakers and wiring them, to consider the common active loads or circuits.

Simply "using 240V" isn't an option in a country like Canada or the U.S. where most branch circuits are 120V as are the devices connected to them.

You can, of course, use a common-internal trip, joined-toggle, 240V circuit breaker to power two separate 120V circuits, possibly sharing a neutral wire, but there are some dangers and inconveniences with that approach as well as the warning that shared neutral circuits can give very troublesome nuisance tripping on AFCI or GFCI circuits that ultimately led to the industry specifically warning that those devices should not be used on a shared-neutral circuit pair

On 2021-09-15 by Hairydog42

Using 240v has advantage of helping balance the load across the 2 legs (L1, L2) of the service. But You need to consume 2 slots instead of 1 in your panel.

On 2021-08-15 by inspectapedia.com.moderator (mod)

@Matt,

Thank you for your comments, we will be sure to review them carefully against the article above.

On 2021-08-14 by Matt

Whoever wrote this has a very poor understanding of either electricity or the English language. I won't make an assumption of which one.

"Twice the electrical power or energy (in current or amps) can be delivered on a # 12 wire by doubling the voltage and holding the current unchanged, "

Uhh no, twice the power measured in Watts can be transmitted through the same conductor.

Also, the whole article misses the main reason that a 220-240V system is more efficient than 110-120V systems. There's some added efficiency as far as the way the that the added current increases some very miniscule loss. The big loss of the North American 110 system is how is each voltage is achieved? The 220V system has both sides of the circuit go through two conductors all the way back to the source (through a series of transformers). A 110 system wired the same would be very negligeable in the increased loss. That's not how 110V works though. There's not a separate 110-120V line coming from the transformer. Instead, there's the two 220-240V feeds. Power is taken from one, and the return is not back through another feed to the transformer, and therefore the plant. Instead, the return is wired to a "neutral". What's a neutral? Basically a ground that is actually grounded at the transformer or right after the panel. Basically the earth is the return, and not a very efficient one. This is where the increase in power consumption comes from.

On 2021-07-12 by inspectapedia.com.moderator (mod)

@Richard,

I think you'll see from the article above that the cost you will be the same

On 2021-07-11 by Richard

Would my electric bill be cheaper if I was using a 240v charger instead of a 120v on my hybred because it would be running for a lot shorter time?

On 2020-10-31 - by (mod) -

Gabriel:

No. From the article above we read

The watts consumed (and therefore the size of your electric bill) for running a water pump or other electric motors will be almost exactly the same regardless of whether you are running the pump wired at 120 Volts or 240Volts.

On 2020-10-31 by gabriel

is there a significant saving by using 220volts clothes dryer rather than 120 volts

On 2020-06-03 by Anonymous

I have circuit 13, circuit 15, circuit 17 running to a 60A disconnect for hvac.

On 2020-06-03 - by (mod) - how many cables do I need to pull to disconnect 3 circuits

Anon

Apologies but I think I'm missing something.
What disconnect? Operating as a sub panel?
Are all 3 circuits wired to the disconnect box or is the disconnect switching another panel into which the circuits are actually wired to individual breakers.

If the latter, the 3 circuits are each routed to their own individual circuit breaker with the proper amperage rating to match the wire size (e.g. 15A #14 Copper, or 20A #12 copper),
and
then from the sub panel a single 60A cable is run to the panel disconnect. Be sure to label mains, sub-mains, etc.

On 2020-06-03 by Anonymous

I have 3 circuits running to 60A 240V disconnect. How many cables do I need to pull to the disconnect?

On 2020-03-30 by (mod) - Residential 220/240 volts is actually 2 lines of 110/120 volts, 110/120 volts to ground but 220/240 volts between both wire

Thanks for the added details, Lee.

On 2020-03-30 by Lee G

Residential 220/240 volts is actually 2 lines of 110/120 volts, 110/120 volts to ground but 220/240 volts between both wires.

Looking at a residential service drop from power pole you will see 2 big black insulated wires, each 1 is 110/120 volts, the big braided support wire is the ground. Behind the service panel that holds all the breaker switches the green and white wires are connected together, the ground wire on an appliance or device is to give the power an alternate path to the breaker box should the white neutral wire be compromised and the breaker will still trip using the green wire and not some unsuspecting person that touches the appliance.

As a side note.... the plugs have 1 wide blade (and 1 normal plus the U shaped grd) so the narrow load (power) blade conducts power directly to the on-off switch as this prevents the device from having complete circuit energized because if it was energized and had a short circuit and plugged in with the blades reversed someone could get electrocuted if they touched it and completed the circuit to grd (wet floor or touching faucet, etc).

On 2020-03-13 - by (mod) - doubling the voltage does not mean that we cut our electric bill in half

Thank you for careful reading, Dennis and for taking the time to comment. I'll review and edit the article above accordingly.

On 2020-03-13 by Dennis Motl

The following statement is WRONG.

But doubling the power or energy does not mean that we cut our electrical bill in half. Why not?

The words "power or energy" should be "voltage"

On 2019-01-26 - by (mod) - can I plug a 220V heater into a 120V wall receptacle?

No, Jim, a 240VAC electric heater, if you could plug it in to a 120VAC circuit (the wall plug won't match the wall receptacle) woul dnot work properly and could be unsafe.

Similarly, a 120VAC electric heater, if you could plug it into a 240VAC circuit, would overheat and risks a fire.

On 2019-01-25 by Jim

I am looking at purchasing a couple small space heaters. The rating is 200/240. Will these work using a 120 Colt plug in?

On 2018-12-24 - by (mod) - more on running an electric motor at higher voltage: dual-voltage motor wiring

Thank for the comment, Chris.

On 2018-07-09 by Chris

In the example of the 120/240 volt ac motor yes you would have twice the voltage and twice the amperage if the motor was rated for 120 VAC only.

A dual voltage motor will have another set of taps to convert it to 240 vac so the current will be halved and the motor will operate normally.

Purchase motors with dual voltage if you want more options.

If you double the voltage and the resistance stays the same the current will follow the voltage and double also.

Watch out: So for example a space heater with only a 120 volt rating that is connected to 240 volts ac will overload and fail caused by overheating and possible fire hazard.

Reader Question: wiring for dual voltage so we can switch back and forth

(Aug 17, 2011) bill abrams said:

it would be nice to wire for dual voltage so I could run the pump from a 120v inverter during a power outage. Any one tried this?

Reply:

(Aug 17, 2011) (mod) said:

Bill the pumps I've worked with (which is not many) had to be opened and jumpers moved to select a power source (for pumps capable of 120/240V.

There is no reason one could not wire up a pump to run either way provided that the switchover included an isolation switch to be sure that it's an "either-or" proposition.

Reader Question: why do we use 12V lights rather than 12V lights in a swimming pool?

(May 21, 2012) nick monte said:

swim pool inground lite - what is the reason for rating pool lights at 12 volts or 120 volts? 12 v is $168.00 vs @324.00. Is it energy cost?

Reply:

Nick, the wiring for 12V is usually smaller, easier to run, less costly; potentially the lower voltage can be less risky.

Reader Comment: 240V common use in Europe saves energy costs on voltage grop

(Aug 21, 2012) Bill said:

In Europe they use 240V to save energy cost on voltage drop. Makes sense, but in US we cannot do so, because our electrical outlets, cords, etc are around Jurassic era!

When visiting Europe our kids cannot get zapped from 240V, because their (in civilized part of EU) outlets are 99% kid proof.

You cannot push metal pins in the outlet, you need a real electrical plug to open those little safety guards.

Here in US, all you need is screw driver to kill your kid in an outlet. Home Depot sells those tamper proof outlets, but if I have them who says my neighbor does so I could send my kids over.

Another thing I've noticed, our plugs hang down revealing those metal pins going into the plug and all you need is to drop metal pin (ie. hangar) crossways on top to get a big boom. In Europe, by the time you'll see metal, it's already disconnected.

What a shame... Time for an upgrade my fellow citizens!

Be safe,
Bill

Reader comments on volts, watts, & current (amps)

5/4/2014 fred said:

110/115/120/220/230/240/1000000 volts.

Appliances use power- That's it. Power is all that matters.

If an appliance is rated say 1KW, 1000 Watts, then if used on a 120 volt supply it needs 1000/120 (amps). That is 8.33 amps.

Another appliance of 1000 watts fed from a 240 volt system would only need 1000/240 (amps) = 4.166.

A further appliance of 1000 watts fed from a 1000 volt supple would only draw 1000/1000 ( amps) = 1 amp.

The designers will work out what current is needed to give the 1000 watts of power the appliance needs knowing the voltage at the place where it will be used. In the UK it will be 230 v. Here it will most likely be 120 volts for a small appliance that only consumes 1KW.

Anything plugged into the typical 120 volt socket/receptacle here in the US will have a rating in watts. Its quite common to say something is a 6 amp vacuum cleaner or drill or whatever. You can say this because the voltage is fixed at 120 so quoting the current is a way to express power. But really the right way to quote something's power is in Watts or KWatts. K means 1000.

Amps times voltage IS Watts. So anytime the voltage goes up the current will go down for the SAME power.
2 amp at 200 volts is 400 Watts. But 20amps at only 20 volts is also 400 watts.

The makers of appliances will work out what current is need to give the power required at 120 volts. They could make an identical appliance but working on 240 volts say and still 400 watts.

You could run something on 240 volts that is not a big load ( takes a lot of current), like a furnace. It does not mean that because you are using a 240 socket that it has to mean a lot of power ( Watts). You might have an electric clock connected to a 240 volt supply, as is common in the UK.

It is power rated at only 2 Watts! So the current it uses is 2W/240V = 0.0083 amp ( 8.3 millamps) - not a lot.

Reply:

Thanks, Fred, your recap of amps, volts, watts, and Kwatts will surely help some readers. I'll copy the text into the article above. Use our CONTACT link to send me an email note if you want to be credited by name, contact info &c.

Details about amps, volts, watts and related terms are found at DEFINITIONS of ELECTRICAL TERMS

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Continue reading  at APPLIANCE EFFICIENCY RATINGS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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Recommended Articles

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• DEFINITIONS of ELECTRICAL TERMS
• EFFICIENCY of 120V vs 240V EQUIPMENT
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