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Too Much Voltage in Your House?

Cost of Electricity from Hydro One, Ontario

Current Situation at My House — Whoa!  After about 10:00 a.m. on 29 November, the voltage at my house averaged 125.77 VAC, a sudden increase of about 4 VAC, at one time reaching as high as 129.1 VAC.  No wonder my UPS power supply has been complaining about the line voltage.  Hydro One -- What are you doing??  For a summary and more details of my measurements, please see Voltage at My House

Digital voltmeter used to test voltage at wall outlet

Too Much voltage at Your House?

There are many causes of the house voltage being too high, most of them technical and resulting from faults in the electrical system either in your own house or between your house and the power distribution system generally.  These pages, however, are concerned with the non-technical cause — that is, that the electricity company has a policy of deliberately setting the voltage higher than it needs to be

This is a long page, covering a number of different aspects of the voltage problem.  The following Overview might be helpful.

Overview –

  1. How Too Much Voltage Will Increase Your Electricity Bill
  2. What Should the Voltage Be?
  3. How to Tell If You Have Too Much Voltage
  4. An Extreme Situation and My Complaint
  5. What Is Going On?
  6. Thermodynamics
  7. Why Does Hydro One Do This?
  8. It's a Bit Like ...
  9. Excuses from Hydro One
  10. The Bottom Line

1.  How Too Much Voltage Will Increase Your Electricity Bill

If your electricity bill is too high, one of the reasons might be that your electricity company is delivering too much electricity, that is, too much voltage, to your house.  Your appliances don't need that extra voltage but you have to pay for it anyway.  My electricity company is Hydro One which delivers electricity directly to most rural and some suburban customers in the province of Ontario, Canada, but many electrical utilities operate in the same way as Hydro One does. 

In North America, most of your electrical appliances are rated to operate with a voltage of 120 volts alternating current (VAC), and allow plus or minus a few volts for variations in load.  If your electricity company, like Hydro One, delivers voltages that are consistently higher than 120 VAC then your appliances will consistently use more power than they need and you have to pay for more energy than you needed. 

Higher Voltage  =  High Electricity Bills !

Too much electricity equals too much voltage, which causes too much current to be drawn, which causes too much power to be dissipated, which, over time, will cause too much energy to be consumed by your appliances. 

2.  What Should the Voltage Be?

The voltage at your wall outlets should be within a few volts of 120 VAC, say 118–122 VAC, depending on the "load", that is, depending on how many and what type of appliances you and your neighbours are using, as well as how far you are from the last transformer.  Further, the average voltage over periods of several days or more should be very close to 120 VAC, and the voltage should be above 120 VAC about half the time and below 120 VAC the other half of the time.  It should be recognized that during periods of extraordinarily high load, such as during very hot or very cold weather, many power generating companies struggle to provide this nominal 120 VAC to their customers. 

All the common domestic appliances that are approved for sale in Canada by the Canadian Standards Association (CSA) are rated to work at 120 VAC (except, of course, the ones rated for 240 VAC). 

Chart of CSA standard 
voltage ranges

The yellow zone in the chart above is the range of voltages measured at my residence during December 2015 and January and February 2016.  (Winter 2015/2016 was not the first winter when I have experienced such high voltages but I hope it will have been the last.) 

The green and red zones are as defined by the Canadian Standards Association document CAN3-235-83 Table 3, "Recommended Voltage Variation Limits for Circuits up to 1000 volts at the Service Entrance".  (See especially the "Voltage Guidelines" on pages 35-36 of the Ontario Energy Board document.)  The Ontario Energy Board states clearly that

Hydro One will supply standard voltages only.  These voltages will conform to Canadian Standards Association (“CSA”) standards.

In fact, these same standards are repeated in Hydro One's statement about conditions of service to Hydro One customers.  (See especially page 49.)  So we know that this standard is used by Hydro One and that the voltage should always be in the green zone and should never be in either of the red zones. 

The CSA recommendation for normal operating conditions is 110–125 VAC, but as any electrician will tell you it can be dangerous to operate for long periods of time at the upper end of that range.  In fact, the same CSA recommendation defines 127 VAC as an "extreme operating condition"

3.  How to Tell If You Have Too Much Voltage

If you have a digital multimeter or other suitable instrument that can measure the appropriate voltage range, check the voltage that appears at the electrical outlets on your walls.  It should be within a very few volts of 120 VAC.  This is an acceptable voltage.  Check it at different times of the day and night for several days to find a reasonable average.  If you find that the voltage at your wall outlets is consistently around 124 VAC or higher, then you have too much electricity in your house and you are using and paying for significantly more energy than your appliances need. 

Please Note —  You are dealing with a potentially lethal voltage, so if you cannot check the voltage safely by yourself, please have a qualified electrician, technician, technologist, or engineer do it for you.  There is no shame in this and it might save your life. 

4.  An Extreme Situation and My Complaint

The winter of 2015/16 brought an extreme situation, as the voltage at my house averaged between 124 and 125 VAC and was higher than CSA's recommended green zone about half of the time, occasionally verging on the upper extreme red zone at 127 VAC.  No wonder my light bulbs burned out that winter, even the expensive CFL lamps, and the high voltage might explain why our expensive HD TV receiver "froze up" for hours at a time in spite of receiving strong TV signals.  While these high voltages have not appeared since then, Hydro One could change their minds at any time and again deliver these extreme voltages. 

In fact, Hydro One continues to deliver voltages that are almost always higher than the nominal 120 VAC.  See here for a summary of the voltages being delivered to my house by Hydro One over the months beginning with December 2015.  While not extreme, these higher voltages cause all of my appliances to use more energy than they need to operate normally.  Details of the monthly measurements are shown in the archive

5.  What Is Going On?

You might remember from your high school physics class that, at 120 volts, a 100 watt incandescent light bulb dissipates 100 watts of power in the form of light and heat.  That is normal and that is what we expect to pay for when we turn on the light switch. 

How Voltage Affects the Power Used
If Your
Voltage Is
Power Used By
A 100 W Load
And You Pay
This Much More
118 VAC 96.6 W -3.3%
120 VAC
100 W 0%
122 VAC 103.4 W +3.4%
124 VAC 106.8 W +6.8%
 126 VAC  110.3 W  +10.3% 
 128 VAC  113.8 W  +13.8% 
 130 VAC  117.4 W  +17.4% 

However, with 124 VAC that same light bulb will dissipate almost 107 watts and you will pay almost 7% more for your electricity.  At 126 VAC, the bulb will dissipate just over 110 watts and you will pay 10.2% more for your electricity.  Your refrigerator, freezer, stove, forced-air heating furnace, electric heaters, sump pump, well pump, washing machine, clothes dryer, coffee maker, many light bulbs — all of these appliances will be similarly affected by the higher voltage that is delivered by Hydro One.  And you will pay for that extra energy.  All the time that they are on. 

The only exceptions to this are electronic devices using "switching-mode power supplies" that are specially designed to operate over a large range of voltages, say, 100-250 VAC.  Within their design range of input voltage these devices do not follow Ohm's Law when calculating their power consumption.  Your cell-phone charger is probably of this type. 

Note to Readers — You win extra points if you have noticed that power and voltage do not have a 'linear relationship' in the chart above.  Except for the switching-mode power supplies already mentioned, the power (and the energy) are proportional to the square of the voltage, so as the voltage is increased, the power and the energy will increase a bit faster than the voltage.  The exact relationship is very accurately described by Ohm's Law.  Ask any engineer. 

6.  Thermodynamics

What does thermodynamics have to do with this?  Well, you might think that the higher voltage would heat things up faster or do other things more quickly, thus compensating for the extra cost of the high voltage.  Certainly, a resistive load like your toaster or hot water heater will heat up faster and then shut off sooner with the higher voltage, but there are still losses due to leakage of the heat, and these losses can never be recovered.  Due to these losses, the shortened heating time at the higher voltage can not completely compensate for the extra cost of operating at a higher voltage.  So, although a toaster (for example) with a higher-than-rated voltage will toast your bread faster than a toaster operated at its design voltage (120 VAC), the design-voltage toaster still costs less to operate than a toaster with a higher-than-design voltage.  As in the quest for perpetual motion, thermodynamics always gets us in the end.

7.  Why Does Hydro One Do This?

To make more money, of course.  Hydro One normally has a surplus of energy to sell, especially during the winter, and they deliver the higher voltages to our homes in order to sell that extra energy to us. 

Once a basic amount of energy has been produced and sold, any extra energy is much cheaper to produce, so profits are high when Hydro One can sell their surplus energy.  As customers, you and I are the buyers of that surplus. 

It is strange that, on one hand, Hydro One is always emphasizing the importance of saving energy by using programmable thermostats, compact fluorescent lights (CFLs), EnergyStar appliances, and paying attention to the Time of Use schedule, while, on the other hand, delivering a level of voltage that cancels out any saving from these conservation efforts. 

8.  It's a Bit Like ...

  • taking your family to an expensive restaurant where the servings are huge and no one can eat all that was put on their plates but the restaurant does not offer a doggie bag service so you have to pay for all the food even though it could not all be eaten;
  • having to buy gasoline at a pump that deliberately overfills your tank and you have to pay for all the gas that spilled on the ground even though you can't use it;
  • having to pay for an extra seat (empty!) every time you take your family to the movie theatre.

9.  Excuses from Hydro One

In years past when I have complained to Ontario Hydro, now Hydro One, about the high voltage at my home, they have given several different "reasons" but none of these reasons is logical or valid. 

  • "But we would have to reduce your neighbours' voltage, too."  —  Doh!  Of course you would.  All of my neighbours' voltages are too high, just like mine, and so should be reduced. 
  • "We like to deliver a higher voltage so that motors will start easier."  —  Excuse me, but I live in a residential neighbourhood, NOT an industrial park, and I can count on one hand the number of significant motors in my home.  All of them are rated at 120 VAC and they work just fine at that voltage. 
  • "But the voltage varies and it isn't high all the time."  —  Yes, the voltage varies alright, and it is the times when it is too high that I am complaining about.  During December 2015, I measured the voltage 135 different times, more or less at random during the days and nights (I'm a bit of an insomniac), and the voltage was never less than 121.0 VAC (already higher than the nominal 120 volts) and as high as 127.2 VAC.  The average of my measurements over the month was 124.25 VAC so my neighbours and I were using about 8% more energy than necessary.  And, Yes, the voltage was still too high most of the time during the rest of the winter.  (See the charts of my measurements for more details.)
  • "But you have it all wrong!  The current decreases as the voltage increases, so the power stays the same."  —  This line was tried on me by several individuals (one of them a professional working in the power industry).  It is a complete mis-statement of Ohm's Law, as can be verified by reference to any physics or electrical engineering textbook.  The general principle of "power stays the same" only applies to electric transmission lines that are fed a constant amount of power from a generating station to a transformer sub-station.  Your home is not a transformer sub-station and is, instead, a "variable load" which requires a constant voltage.  See more details here.  To claim that "the power stays the same" is a lie, contrary to the laws of physics, and is a neat piece of propaganda used to hide from factual criticism of the power industry.  It might work on politicians and some journalists, but it doesn't work on me and it shouldn't work on you. 

All of this from Hydro One and the power industry, who like to paint themselves as guardians of conservation and energy efficiency.

10.  The Bottom Line

Ideally, the average voltage over a 24-hour period should be 120.0 VAC and vary between, say, 117 and 123 volts, or better between 118 and 122 volts, depending on supply and load conditions.  So, the voltage should be above 120 volts about half the time and below 120 volts the other half of the time.  Hydro One should strive to achieve that level of supply for all residential neighbourhoods.  That is fair and proper and does not cause our appliances to use more power and energy than they are supposed to or cost us more money than we should have to pay.  At my home, however, my measurements have shown that the voltage is more than 120.0 VAC more than 80% of the time since at least the beginning of 2018, except for just four months, November and December 2018, and June and July 2019.  Only in November 2018 was the voltage above 120 VAC only about 50% of the time.

Percentage of time voltage 
is more than 120 VAC

With smart meters and other telemetry systems, Hydro One knows exactly how much voltage they are supplying and have no excuse for not being aware of the excess and costly voltages that I have described above. 

The results of many measurements at my own home are summarized here.  It is necessary to take a large number of measurements each month (now about 4,000 automatic measurements each month) in order to assure accuracy and to overcome the effects of hour-to-hour and day-to-day variations in load and in capacity of supply. 

The voltage measurements for last month are summarized here. Please also see the archive of measurements for previous months (back to December 2015).