Troubleshooting & Repairing Commercial Electrical Equipment
Answers to RF Cafe Quiz #65

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Troubleshooting & Repairing Commercial Electrical Equipment - RF Cafe

This quiz is based on the information presented in Troubleshooting & Repairing Commercial Electrical Equipment, by David Herres. The book provides a wealth of information on commonly encountered electrical gear and identifies the kinds of problems most likely to be seen. Mr. Herres recommends ways to help prevent the situations from occurring in the first place as well as typical approaches for troubleshooting and repair used by seasoned professionals. I have to admit that I had completely forgotten about the nickname of "Wiggy" which has been bestowed upon one of my favorite electrical test instruments.

Note: Some of these books are available as prizes in the monthly RF Cafe Giveaway.


Autotransformer - RF Cafe1. What is an autotransformer"

d)  A transformer whose secondary winding is part of the primary winding

That autotransformer has a single winding that serves as both the primary and the secondary. The disadvantage is that electrical isolation is not provided.

(see page 17)





Full-Wave Rectifier - RF Cafe2. What is the circuit to the right called?

c)  Full-wave rectifier

A full-wave rectifier conducts on both the positive and negative half-cycles of the AC supply. A half-wave rectifier would use a single diode and only conduct on either the positive or the negative half-cycle.

(see page 21)





Volt-test® Solenoid Voltage Tester - RF Cafe3. What is a Wiggy?

a)  A voltmeter that uses a solenoid meter rather than a d'Arsonval meter movement.

Named after its inventor, George P. Wigginton, a "Wiggy" is a type of voltmeter that uses a solenoid whose plunger's displacement indicates the applied voltage level. It is very rugged and has no range selectors, making it easy to use. The audible 'clack' that occurs when energized, and the tactile vibration (a wiggle, or even a 'wiggy') when measuring AC makes it a great tool when used in an environment where actually reading a displayed voltage value is difficult. I still have and use my Squared-D model that I bought back in the 1970s.

(see page 35)




4. What are the two basic components of all electric motors?

d)  Stator and rotor

The stator (non-rotating component) and rotor (rotating component) are the two main parts of every electric motor.

(see page 48)




SPDT Switch Symbol - RF Cafe5. What does this schematic symbol represent, and what is a common use for it in residential electrical wiring?

d)  A 3-way (SPDT) switch, used for controlling lights from two different locations

A single-pole-double-throw (SPDT) switch is referred to in the electrical trade as a 3-way switch. The '3-way' moniker might not make sense because it seems there are only two positions: c-a and c-b. However, there is a third position ('way') available in some switches: Neither c-a nor c-b. Hence, '3-way.' This schematic shows one method for wiring a pair of 3-way switches to permit control of a light from two different locations.

(see page 84)




6. How does a ground fault interrupter circuit (GFIC) device work?

d)  A comparator circuit cuts off the supply if the current through the neutral (return) is not the same as the current through the feed (hot) wire. It only requires less than 100 mA of current through the human heart to send it into fibrillation, so the comparator has a pretty tight tolerance. The GFIC device does not require a ground connection at all in able to function.

(see page 86)




7. What does SCADA stand for?

a)  Supervisory Control and Data Acquisition

SCADA has been used by, among other entities, public utility companies to provide real-time monitoring, reporting, and control of facility functions from a remote location. Various implementation use wireless (RF), telephone, cable, and power line carrier as the transmission medium between the facility and the central office.

(see page 105)




8. What is the difference between a heterodyne (het) and a superheterodyne (superhet) receiver?

c)  Het uses direct conversion while superhet uses an IF

The heterodyne radio circuit was developed by Reginald Fessenden and uses a single frequency conversion stage. Edwin Armstrong developed the superheterodyne receiver that uses an intermediate frequency (IF) from the first mixing process (frequency conversion), and a second conversion from IF to baseband (BB).

(see page 123)




RJ11 Telephone Jack - RF CafeRJ45 Ethernet Jack - RF Cafe9. What does the 'RJ' part of communications jacks stand for (e.g., RJ11, RJ45)?

a)  Registered Jack

'Registered jack' is vintage AT&T terminology. The RJ11 is your common household telephone type jack. The RJ45 is a standard Ethernet jack.

(see page 138)




10. What is 'by far' the most common cause of elevator malfunction?

b)  The door did not close completely

Safety mechanisms prevent the elevator locomotion mechanism from engaging if the door does not close properly, so nothing ese works unless the door is closed.

(see page 163)