For many years the American Electrician's handbook has described the use of a Mershon diagram for finding voltage drop. The Diagram in the AEH is about 2 inches square. Does anyone know where a larger diagram can be found?
If I could find my AEH, I would give a detailed account. What the heck, I am going into Fairbanks this PM; I will stop by Barnes and Nobel and buy the new one I was looking at a couple days ago, and let you know. They have three methods of finding voltage drop in the AEH, and it has been there for a long time. But I don't think most people read the AEH. I haven't read it in about 25 years. I did search for Mershon at Google and found a grave site for a rather famous EE. I think he was a renowned inventor back in the 20th century. I also went up to the University of Alaska EE dept several years ago and asked the power Prof about it and he never heard of it.
I did find this. Apparently he was a Mechanical Engineer, and he was the founder of the college ROTC program.
RALPH DAVENPORT MERSHON, both an excellent engineer and an american patriot, worked untiringly for the goals and ideals he deemed important to society. In his passing he served to perpetuate his work through his generous contribution to The Ohio State University where he received his formal education.
Dr. Mershon was born in Zanesville, Ohio, July 14, 1868 and passed on --------, 1952. He graduated from the Mechanical Engineering Department of The Ohio State University in 1890. From 1891 to 1900 he worked as an engineer at Westinghouse Electric and Manufacturing Company. While at Westinghouse his inventive skill and dedication combined to produce many devices for which he was granted a total of thirteen patents. The Compensating Voltmeter and 6-phase Rotary Converter are two of his inventions. In 1900 he left Westinghouse and began a private consulting practice where he designed various electrical power plants in the United States, South Africa and Japan. He was chief engineer during the designing and construction of the Niagara, Lockport and Ontario Power Company and was a pioneer in measurements of electrical transmission. During his career Dr. Mershon was granted a total of 93 patents.
RALPH D. MERSHON'S career was interrupted by World War 1 where he served as a Major in the Engineers Officer's Reserve Corps and then as a Lieutenant Colonel in the Engineers Corps. He was in active service from 1917 to 1919 detailed to the Naval Consulting Board. During the early days of the war Colonel Mershon, in conjunction with Brigadier General Edward Orton, Ohio State Graduate, Ohio State President, William Oxley Thompson and Colonel George L. Converse, held a series of meetings respecting a need for a comprehensive plan embracing military training in the country's educational institutions. This evolved into the "Ohio Plan" for training of reserve officers. It was presented to the Military Affairs Committee of the House of Representatives and was incorporated into the National Defense Act of 1916. This dream of Colonel Mershon became the Reserve Officers Training Corps (ROTC).
Degree of Mechanical Engineer - The Ohio State University - June
Honorary Degree of Doctor of Engineering - The Ohio State University
Honorary Degree of Doctor of Engineering - Tufts College - 1936
That's a kind of nomograph. Those were popular in the days before programmable calculators, PCs and PDAs.
Nomographs necessarily make some simplifying assumptions to make their use simple, or in some cases possible. If you want one for the sake of nostalgia, I'd suggest looking in the engineering/science section of a good used book store. If you want one for design work, I'd suggest pursuing a more up to date solution.
Nostalgia might be the reason for wanting to ask about the Mershon Nomograph. As we look back so little credit is given to individuals that have done so much. It seems unfair that the only thing left for us to remember him by is a headstone in Ohio with the initials R.D.M. Maybe the history channel will do something on this. As for an up to date solution, we electricians for the most part are still using ohm's law to find voltage drop.
I appreciate all this engineering advice, but we still use ohm's law. The basic formula for voltage drop is VD = (2*k*L*I/CMA) * Multiplier (or else we simply use the 75 degree resistances from Table 8 from Chapter 9 of the NEC.)
Multiplier is 1.0 for single phase, 0.866 for three phase 3 wire and
0.5 for 3-phase 4 -wire and K=12.9 for copper and 21.2 for aluminum. This is the formula you had better use if you want to pass the electrician journeyman's test.
That is about all there is to it. I might add it works fine for us electricians and apparently has for the last fifty or so years. For Corps jobs the rule of thumb is size up for every 70 feet for No. 12 AWG on 20 ampere circuits.
As for Maxwell and voltage drop, we leave that for the engineers on the big design jobs. There aren't enough of them to go around so we often have to do our own field designs for the smaller shop jobs.
--------- For what you are doing, the theory has been reduced to a set of rules or formulae. Nothing wrong with that. Paul is trying to point out some of the background behind such rules. They work very well as you know but there are situations where they don't work well. You may not run into these situations but will run into situations where you know just what practical problems arise where a more theoretical person may not (e.g. being used to considering transmission systems where line inductance is more important than resistance, I did lose sight of the fact that in commercial/residential and some industrial distribution, resistance is the dominant factor -and was corrected by an electrician- was it you- if so -thanks). I hope that "engineers" do learn from "electricians" as well as the other way around.