Energy Audit-High Voltage

High Voltage, the first thing that comes to mind is AC/DC’s 1976 album of the same name.  (I was 7 when that album was released.)  An awesome first album from a band that eventually becomes one of classic rocks best.  But high voltage can be a big problem with electronics and electrical equipment in houses and businesses.  My brother, who is an electrical engineer and master electrician, gave me the idea for this blog post.  He had to recently trouble shoot a problem.

A customer called stating that he was constantly changing the the heating elements in his electric water heater.  They were failing every couple week.  My brother was called in to figure out why. 

Lets look at the basic electric water heater.

The typical electric resistant water heater has a couple heating elements, much like the one in the picture below.

Electric water heating element
Stamped electrical listings on an electric water heating element

As you can see in the above photo, this element is design to operate at 240 volts and draws 4500 watts, which will cost in my area around $.55 per hour for each hour the water heater operates. We can determine some additional information about the electrical properties of this heating element by using Ohms Law.

Ohms Law

We can calculate the amperage of the element by using the stamped information on the element and the Ohms Law formula of I=P/E. Amperage equals watts divided by voltage. I=4500 watts / 240 volts or 18.75 amps. The amperage of the element will determine the size overcurrent device or breaker needed for the water heater. We can also determine the resistance in ohms by the formula R=E²/P, resistance equals voltage squared divided by power. R=240²/4500 or 12.8 Ohms. We now have the following information about the electric resistant water heater element. Stay with me, the information does become critical in solving the issue with the problem water heater.

P or Watts = 4500 watts (or 4.5kW)

I or Amperage = 18.75 Amps

E or Voltage = 240 Volts

R or resistance = 12.8 Ohms

During the trouble shooting of the water heater, my brother discovered the voltage of the home was higher than normal, 135/270 volts, most homes operate between 120/240 volts and 125/250 volts. I have measured voltages nearing 130/260 volts, but never as high as my brother tested.

The voltage at my home.

So, how does a higher voltage effect electric resistance heating elements? We have to go back to Ohms Law and the formula for solving P or Wattage. E²/R=P, the voltage has increased above the stamped listing on the water heater element. 270²/12.8 = 5695 Watts or an increase of 1195 watts over the listing stamped on the element! The increase of 30 volts drastically changed the amount of power running through the element, causing them to fail. The increase also changed the cost to operate the water heater. Originally costing around $.55 per hour, the new cost increased to just over $.70 per hour.

A lesson learned! It’s rare I enter a home with a high electrical bill complaint and check the electrical system for the voltage the home is operating. Something I will be doing from now on…hopefully you can also appreciate the impact of “High Voltage”.

Took this picture of AC/DC’s Angus Young during a 2016 concert, High Voltage!

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