# GEORGE W. FARRELL and FRANK R. VALVODA, P.E.

### Articles

Electrical and Power October 17, 2006

## The Art of Protecting Electrical Systems, Part 10: Assigning Impedance Values

Editor’s Note: From 1965 through 1970, Consulting-Specifying Engineer’s predecessor, Actual Specifying Engineer, ran a series of articles on overcurrent protection. Due to the immense popularity of the 31 installments in the series, the authors, George Farrell and Frank Valvoda, P.E., reprised the series in an updated version beginning in the Feb. 1989 issue of CSE.

By GEORGE W. FARRELL and FRANK R. VALVODA, P.E.
Electrical and Power August 15, 2006

## The Art of Protecting Electrical Systems, Part 8: Short-Circuit Calculations

This installment of our ongoing series introduces short-circuit calculations, starting with the fundamentals and proceeding on through available computer programs. In previous articles, we discussed the importance of overcurrent protection, presented fundamental theorems used in short-circuit calculations and examined component short-circuit ratings. This article begins the study of calculation methods. The fundamental electrical quantities used in short-circuit calculations are voltage, current and impedance, i.e., Current = K1 x K2 where K1 is a constant, depending on whether the circuit is single-phase or three-phase, and K2 is a constant by which the various levels of voltage and kVA in a distribution system system are related to each other. Typical short-circuit calculations are carried out using line-to-neutral values of impedance, with K1 = 1. Tabulated values of impedance for conductors and other circuit components are always given in line-to-neutral ohms.

By GEORGE W. FARRELL and FRANK R. VALVODA, P.E.
Building Automation and Controls July 18, 2006

## The Art of Protecting Electrical Systems, Part 7: Equipment Short Circuit Ratings

Editor’s Note: From 1965 through 1970, Consulting-Specifying Engineer ’s predecessor, Actual Specifying Engineer, ran a series of articles on overcurrent protection. Due to the immense popularity of the 31 installments in the series, the authors, George Farrell and Frank Valvoda, P.E., reprised the series in an updated version beginning in the Feb. 1989 issue of CSE.

By GEORGE W. FARRELL and FRANK R. VALVODA, P.E.