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 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 such 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 and relay troubleshooting chart.

 

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