Who Really Won the Current War? The path to adopting DC wiring standards

Shutterstock / Zizou7
Shutterstock / Zizou7
Published On
Jul 15, 2021

I ran across an article claiming we will soon be installing DC wiring and outlets in residential and commercial projects. The article posed the question, “Will Edison win after all?” For anyone unfamiliar with this reference, Thomas Edison went to war with Nikola Tesla and George Westinghouse over whether AC or DC would become the standard for delivering electricity. Edison lost, so the standard became AC. AC won for several reasons, including costing less to transmit over long distances and the invention of the AC motor.

The way we use power, however, has changed over the last 40 years. It started slowly, with the first personal computers, but has accelerated quickly in the last decade. Today, much of our power use is DC. LED lamps, computers, phones, tablets, televisions and even refrigerators are converting AC to DC to power the electronics in them. This conversion is only 70%–90% efficient. A loss of 10%–30% does not sound like a big deal in a device that only delivers a couple of amps, until you do the math. It is estimated that 5 billion new electronic devices are manufactured every year. Even a 10% loss in that many devices matters a lot.

Adding to that loss, the AC/DC adapters plugged into AC outlets draw power even when not in use. I recently read about one person’s experiment in which he turned off every electrical load in his house but still had a current flow of 2.6A. When he unplugged all the adapters in his house and measured the current again, the flow was eliminated.

In addition, we face increasing power losses from AC to DC conversion due to the rising proliferation of electric vehicles. EV chargers draw significantly more amperage compared to standard consumer electronics. I checked out Tesla’s vehicle charging guide and found demands ranging from 15–60A for the AC charging circuit. A 10% loss on a 60A circuit is significant, considering that users may be charging their vehicles every day.

There are many ongoing efforts to increase the efficiency of AC to DC power supplies. However, why not consider eliminating them altogether? Why not have a DC distribution network in homes and offices? If you consider the rapid expansion of buildings that generate their own DC current, it makes even more sense. Solar panels generate DC power, which can be distributed to DC devices with no AC-to-DC conversion losses. There is also presently a campaign for installing battery storage systems, with some utilities offering rebates. The batteries store excess energy from solar panels during daylight hours and release it on demand at night.

Pre-adoption problem-solving

Several problems need to be solved before we can achieve adoption of DC wiring standards. My first question is where do we get enough DC to power larger loads such as vehicle chargers, air conditioners and large appliances? While an average solar panel system could deliver enough current for all the electronic devices in a house or office, it will not be able to charge vehicles or run large appliances.

During my research for this article, I found many stories proposing various solutions. One in particular caught my attention: modern technology has come up with new ways to build large AC-to-DC power supplies with efficiencies of 95% and higher.

OK, so we have highly efficient, large DC power supplies. How do we get that current to the device? What voltage will be standard? What kinds of outlets are available? How do we power large AC appliances? All these issues are being worked on, but it will take a while to come up with standards. I have read many proposals, including using the existing AC outlets for DC, dual-system wiring in new construction and DC-only wiring in new construction. Only time will tell how these questions are answered.

During my research, I found out that the original reason Edison lost the war over current standards has been eliminated. In the 1800s, DC could not be efficiently transmitted over long distances, but now it can. High-voltage DC transmission technology is more efficient over long distances, compared to high-voltage AC transmission. This technology, which has been around for many years, continues to improve and gain in popularity. Maybe some day in the future, we will have DC delivered from the utility company to our homes and facilities.

I only have space here to scratch the surface of this subject, and I intend to write about it again as I learn more. I would like to hear from anyone who has had experience with DC in the home or office environment. Email me at the address below.

About the Author

Stephen Carr

Estimating Columnist

Stephen Carr has been in the electrical construction business since 1971. He started Carr Consulting Services—which provides electrical estimating and educational services—in 1994. Contact him at 805.523.1575 or steve@electrical-estimating.com, and...

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