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Test Your Motor Control IQ

Feb 1, 1998 12:00 PM, Larry Baran

What should voltage readings be at various points of a control schematic?

Shown here (illustration is in original, printed article) is a wiring schematic of an across-the-line starter with 480-120V control transformer. Based on each of the operating conditions shown below, fill in each table with what you think the voltage readings should be between the points indicated.

Condition 1: 480V power ON; Disconnect 1 OPEN; M coil and motor OFF; OL1 contact CLOSED.

Condition 2: 480V power ON; Disconnect 1 CLOSED; M coil and motor OFF; OL1 contact CLOSED.

Condition 3: 480V power ON; Disconnect 1 CLOSED; M coil and motor ON; OL1 contact CLOSED.

Condition 4: 480V power ON; Disconnect 1 CLOSED; M coil and motor OFF; OL1 contact OPEN.

Condition 5: 480V power ON; Disconnect 1 CLOSED; Fuse 1 OPEN; M coil/motor OFF; OL1 contact CLOSED.

Condition 6: 480V power ON; Disconnect 1 CLOSED; Fuse 2 OPEN; M coil/motor OFF; OL1 contact CLOSED.

Answers (in boldface): Condition 1: L1-L3: 480V; T1-T3: 0V; H1-H4: 0V; X2-X1: 0V; X2-A: 0V; X2-B: 0V; X2-C: 0V; X2-D: 0V; X2-E: 0V

Condition 2: L1-L3: 480V; T1-T3: 0V; H1-H4: 480V; X2-X1: 120V; X2-A: 0V; X2-B: 0V; X2-C: 120V; X2-D: 120V; X2-E: 120V

Condition 3: L1-L3: 480V; T1-T3: 480V; H1-H4: 480V; X2-X1: 120V; X2-A: 0V; X2-B: 0V; X2-C: 0V; X2-D: 120V; X2-E: 120V

Condition 4: L1-L3: 480V; T1-T3: 0V; H1-H4: 480V; X2-X1: 120V; X2-A: 0V; X2-B: 0V; X2-C: 0V; X2-D: 0V; X2-E: 120V

Condition 5: L1-L3: 480V; T1-T3: 0V; H1-H4: 0V; X2-X1: 0V; X2-A: 0V; X2-B: 0V; X2-C: 0V; X2-D: 0V; X2-E: 0V

Condition 6: L1-L3: 480V; T1-T3: 0V; H1-H4: 480V; X2-X1: 120V; X2-A: 0V; X2-B: 0V; X2-C: 120V; X2-D: 120V; X2-E: 120V

Contact author at Starrats Technical Services, P.O. Box 436, Riverside, IL 60546; phone 708-484-2477; fax 708-484-2487; and e-mail STARRATS@COMPUSERVE.COM.

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