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Handbook of Electrical Design Details P2

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Power riser diagram for a combined office-warehouse building. the motor it will control. The contactors, overcurrent protective devices, transformer, and operating coil are in one enclosure, and the start/stop pushbuttons are in a separate enclosure so that they can be mounted some distance from the motor. In this schematic each component is represented by a graphic symbol, and each wire is shown making individual connections between the devices. However, multiple wires could appear as one line on the drawing. As on this drawing, each wire is usually numbered to indicate where it enters the enclosure, and those numbers are repeated for. | ELECTRICAL PROJECT DRAWINGS 27 Current xfmr cabinet Rooftop AH unit no. 1 Rooftop AH unit no. 2 Busway typical 4 No. 6 AWG in 2 conduit 3 No. 10 AWG in 3 4 conduit 3 No. 6 AWG in 1 conduit Main panel 3 No. 6 AWG in 1 conduit Panel A 4 No. 2 in 2 conduit 4 No. 4 0 AWG in 3 conduit . Ground in accordance 8 350 kcml in with NEC Article 250 2 3.5 conduit Figure 1-8 Power riser diagram for a combined office-warehouse building. the motor it will control. The contactors overcurrent protective devices transformer and operating coil are in one enclosure and the start stop pushbuttons are in a separate enclosure so that they can be mounted some distance from the motor. In this schematic each component is represented by a graphic symbol and each wire is shown making individual connections between the devices. However multiple wires could appear as one line on the drawing. As on this drawing each wire is usually numbered to indicate where it enters the enclosure and those numbers are repeated for the same wires connected inside the enclosure. The three supply wires are identified as L1 L2 and L3 the motor terminals are designated T1 T2 and T3 and the normally open line contactors controlled by the magnetic starter coil C are designated as C1 C2 and C3. Each contactor has a pair of contacts that open or close for control of the motor. The remote control station consists of the stop and start pushbuttons connected across lines L1 and L2 by the primary of an isolation control transformer. The transformer secondary in the control circuit is in series with the normally closed overload contactors OC and the magnetic starter coil C . The stop button is also connected in series with the starter coil and the start button is connected in parallel with the starter coil. 28 PLANNING FOR ELECTRICAL DESIGN In this circuit the control transformer isolates the control circuit mid prevents it from responding to any ground faults that could cause the motor to start accidentally. The isolating .