Cover of Hawkins Electrical Guide v. 03 (of 10) Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to — Story, Setting & Ideas

Hawkins Electrical Guide v. 03 (of 10) Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to — Story, Setting & Ideas

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In Category - Electrical Technology

Authors: Hawkins, N. (Nehemiah), 1833-1928 Digital Source: Project Gutenberg Gutenberg Release Year: 2015 First Publication Year: Not confirmed

Key Word: Electrical engineering -- Handbooks, manuals, etc. Target Reader: Readers of public-domain and historical texts

Book Edition: Project Gutenberg digital edition Book Language: en

Edition facts

Words 74,369

Reading time 324 min

Text sections 13

For Hawkins Electrical Guide v. 03 (of 10) Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to — Story, Setting & Ideas, the stored edition analysis reports 74,369 words, 5 hr 24 min estimated reading time, and 13 detected text sections.

The text analysis averages about 20.4 words per sentence, while the detected sections provide another way to judge how the source is divided.

Project Gutenberg metadata also associates the work with “Electrical engineering -- Handbooks, manuals, etc.,” connecting these edition facts with the source record’s subject description.

Source: Project Gutenberg record #49769

This third volume of Hawkins' Electrical Guide focuses on galvanometers, testing apparatus, and dynamo operation, using a question-and-answer format with detailed diagrams. It covers instruments like the D'Arsonval galvanometer, Wheatstone bridge, and watt-hour meters, and includes practical advice on reducing electricity waste.

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File: pg49769

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o be 332. Substituting these values in the above formula: d = (332 × 54.07) ÷ (1,000 × 16.46) = 1.09 miles.]

Ques. How may the distance from 2 to the fault be determined in knots or miles.

Ans. Divide Y by resistance per knot or mile.

The Varley Loop.--This is a method of locating a cross or ground in a telephone or telegraph line or other cable by using a Wheatstone bridge in a loop formed of a good wire and the faulty wire joined at their distance ends. One terminal of the battery is grounded and the other connected to a point on the bridge at the junction of the ratio arms. The rheostat arm then includes the resistance of the rheostat plus the resistance of the fault, while the unknown arm includes the resistance of the good wire plus the resistance of the bad wire beyond the fault. When the bridge is balanced, the unknown resistances may be readily determined by a simple equation.

In making the Varley loop test, the resistance of looped cable or conductors is measured, and then connected as in fig. 598. Close the battery key and adjust R for balance.

When earth current is present, the best results are obtained when the fault is cleared by the negative pole, and just before it begins to polarize. If X be the resistance from 2 to the fault, then X = (L - R) / 2

also, X divided by the resistance of the cable or conductor per knot or mile gives the distance of fault in knot or miles.

When the resistance of the good wire used to form a loop with the defective wire, together with that portion of the defective wire from the joint to the fault is less than the resistance of the defective wire from the testing station to the fault, the resistance R must be inserted between point 1 and the good conductor, the defective wire being connected directly to point. The formula in this case is X = (L + R) / 2

Special Loop.--This method may be used to advantage where the length of the cable or faulty wire only is known and where there are two other wires which may be used to complete the loop. It is not necessary that the resistance of the faulty wire and the length and resistance of the other wires be known. Figs. 601 to 604 show the connections and method of testing.

EXAMPLE.--All the wires in a cable 10,852 ft. long were found to be grounded so that none of them could be used as good wires. Two wires were selected out of another cable going to the same place by a different route and securely joined to one of the grounded wires at the distant end. This grounded wire and one of the good ones were connected as shown in figs. 601 and 602 and the reading A was found to be 307. Connections were then made as shown in figs. 603 and 604 and A was found to be 610. What is the value of d?

d = AL/A = (307 × 10,853)/610 = 5,461 ft.

The Potentiometer.--For the rapid and accurate measurement of voltage, current, and resistance, the potentiometer can be recommended. Those in charge of electric light and power companies, and also those who purchase large amounts of electrical energy are realizing, more and more, the necessity of having satisfactory primary standards with which to check their volt-, ampere-, and watt-meters.

When it is realized that an error of one per cent. in a commercial instrument means an error of one dollar one way or the other in every one hundred dollars charged, the need of such standardization apparatus becomes at once apparent.

The potentiometer, it should be noted, relies for its accuracy, only upon the constancy and accuracy of resistances and upon standard cells.

With the materials now available, and the skill which has been acquired in their manufacture, both the resistances and the standard cells are obtainable which are remarkably constant, and both can be readily checked for accuracy.

Location of Opens.--These measurements are based on the fact that the capacity of wires in a cable is ordinarily a measurable quantity, which, in wire of uniform diameter, is proportionate to length. In making these tests, a fault finder is used together with a buzzer, dry cells to operate it, small induction coil, and telephone receiver. These instruments are to be found in any telephone exchange. It is best to locate the buzzer at some distance from the fault finder in order that it cannot be heard by the operator.

Before attempting locations for opens it is well to make the following measurements:

1. The insulation of the broken wire and the insulation of the good wire with which it is to be compared.

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This third volume of the ten-part Hawkins Electrical Guide concentrates on measurement and testing instruments, from galvanometers to the Wheatstone bridge, and concludes with operational procedures for dynamos. The book's question-and-answer structure—each chapter posing a series of queries then supplying detailed responses—reflects its stated motto: “The thought is in the question; the information is in the answer.” The text assumes a reader who already possesses basic electrical knowledge and seeks practical, hands-on guidance. Diagrams are integral: figures such as the internal connections of the Duncan watt-hour meter (Fig. 663) are described in precise mechanical terms, with attention to components like “micrometer screw brush adjustment” and “soft iron bridge plate.” The volume also includes a notable section on preventing electricity waste in large residences, advising meter readings before and after bedtime to detect overnight usage.

Galvanometer Types and Their Adjustments

The galvanometer chapter opens with a distinction between a galvanoscope and a galvanometer—the former merely indicates current, while the latter measures it. The text then systematically describes several types: the astatic, tangent, sine, differential, ballistic, and D'Arsonval galvanometers. For each, the explanation centers on construction and calibration. The tangent galvanometer, for instance, is explained through a “mechanical explanation of tangent law,” and a table of natural sines and tangents is provided for scale graduation. The D'Arsonval instrument receives particular attention: its operation depends on a moving coil in a permanent magnetic field, and the text notes its use of mirrors and a lamp-and-scale arrangement for reading small deflections. The concept of “damping” is introduced, and the galvanometer constant—or “figure of merit”—is defined as a key specification. Shunts are discussed as a means to extend the instrument's range.

Resistance Measurement and the Wheatstone Bridge

A substantial portion of the volume is devoted to testing apparatus and methods for measuring resistance. The text covers the Clark and Weston cadmium cells as voltage standards, and explains the International volt, ampere, and ohm. Several methods for resistance measurement are enumerated: direct deflection, substitution, fall of potential, differential galvanometer, drop, and voltmeter methods. The Wheatstone bridge receives the most detailed treatment, including the arrangement of ratio coils, the “decade plan,” and the distinction between “plug out” and “plug in” resistance boxes. Practical testing sets, such as the Queen Acme set and the Evershed portable ohmmeter, are described with diagrams. The Kelvin wire bridge is introduced for measuring low resistances. Loop testing methods—Murray, Varley, and special loops—are illustrated for locating faults in cables.

Dynamo Operation and Practical Energy Saving

The final chapter, “Operation of Dynamos,” provides a step-by-step inspection checklist before starting a dynamo or motor. The reader is instructed to examine field magnet circuits, clean and oil bearings, check the air gap between armature and pole faces for foreign objects, inspect armature windings and insulation, and rotate the armature by hand to ensure free movement. The text also addresses the commutator and brushes. A separate, shorter section titled “Waste of Electricity in Lighting” offers practical advice for large residences: read the meter before retiring and again in the morning to detect overnight waste; use smaller lamps (8 or 4 candle power) in bathrooms, halls, and cellars; and replace old, dim lamps because an old 16-candle-power lamp that gives only 8 candle power consumes nearly the same current as a new one. The advice is concrete and aimed at the person paying the bills.

Readers approaching this volume will benefit from having a basic understanding of electrical circuits and terminology, as the question-and-answer format assumes prior knowledge. The book is best used as a reference: one can consult specific chapters on galvanometers, resistance measurement, or dynamo operation without reading sequentially. The numerous diagrams and tables—such as the table of galvanometer constants and the natural sines and tangents table—are essential for calibration and should be studied alongside the text. The practical tips on energy saving, though brief, offer a glimpse into early 20th-century domestic electrical management.

Some evenings, I recall how the Hawkins Electrical Guide taught me to measure invisible currents with patient instruments—galvanometers, bridges, quiet needles. It feels much like reading Notes Upon Indigo — Text and Context, where dye, too, is coaxed from a humble leaf. Both books speak of unseen forces turned useful, with care, not force.