Identifying Motors

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  Identifying Motors   Electric motors with no identification (no nameplate or lead tags) must often be maintained and repaired. Follow these steps to determine an unknown motor’s characteristics, based on the NEMA Standard method of motor identification. First, sketch the coils to form a wye. Identify one outside coil end with the number one (1), and then draw a decreasing spiral and number each coil end in sequence as shown in Figure 6-3. Using a DMM, ohmmeter, or continuity tester, the individual circuits can then be identified as follows: Step 1. Connect one probe of the tester to any lead, and check for continuity to each of the other eight leads. A reading from only one other lead indicates one of the two-wire circuits. A reading to two other leads indicates the three-wire circuit that makes up the internal wye connection. Step 2. Continue checking and isolating leads until all four circuits have been located Tag the wires of the three lead circuits T-7, T-8,...
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Troubleshooting Luminaires (Lighting Fixtures)

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Troubleshooting Luminaires (Lighting Fixtures)

 

Luminaire. A complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps and ballast (where applicable), and to connect the lamps to the power supply.

A typical commercial, industrial, or institutional building contains hundreds or even thousands of luminaires. For this reason, troubleshooting luminaires is an important part of the typical maintenance electrician’s work. This chapter covers the three most common types of lighting used in commercial, industrial, and institutional applications:

o   Fluorescent luminaires

o   Incandescent luminaires

o   High-intensity discharge (HID) luminaires

 

Troubleshooting Fluorescent Luminaires

Fluorescent lamps are electrical discharge lighting sources. Current flows in an arc through a glass tube filled with mercury vapor between contacts called cathodes at each end of the tubular lamp. The inside of the tube is coated with a powder called phosphor that glows when excited by ultraviolet radiation, producing visible light.

Fluorescent lamps require an auxiliary component called a ballast to operate. The ballast performs two functions:

1.      It produces a jolt of high voltage to vaporize the mercury inside the lamp and start the arc from one end to the other.

2.      Once a lamp is started, the ballast limits current to the lower value needed for proper operation.

There are many different types of fluorescent lamps and ballasts. Older types of ballasts known as core-and coil are still widely used, but electronic ballasts are also common.

Almost all fluorescent luminaires installed in modern construction use rapid start and instant start lamps. An older type of preheat fluorescent lamp uses a separate component called a starter to heat the lamp cathodes before the arc is struck. Preheat lamps and fixtures are rarely used in modern commercial lighting systems, and they are not included in this troubleshooting guide.

 

 

The troubleshooting chart (Figure 5-1) lists faults, probable causes, and corrective action to take while troubleshooting fluorescent luminaires.

 

5-1 Troubleshooting chart for fluorescent luminaires.

 

 

 

 

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Troubleshooting Relays and Contactors

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  Troubleshooting Relays and Contactors   Relay is an electromagnetic or solid-state device used in control circuits of magnetic motor starters, heaters, solenoids, timers, and other devices. They are frequently used for remote control applications. Relays are manufactured in a number of different configurations, in both mechanical and solid-state designs. Figure 8-1 shows a type of relay often used to control small, single-phase motors and other light loads suc h as heaters or pilot lights. Contactors are electromagnetic devices similar in construction and operation to relays, but designed to handle much higher currents (Figure 8-2) involved in applications such as switching large banks of stadium lights on and off. Figure 8-3 describes troubleshooting procedures for relays and contactors. 8-1 Single-pole, single-throw (SPST) relay rated 30 A, 600 V.   8-2 NEMA size 1 contactor rated 10HP, 575 V.     8-3 Contactor...
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