Case study # 1.3 Title Acoustic noise troubles caused by switching noise of an elevator (lift) Type of trouble Acoustic noise. Source of trouble Elevator. System affected Customer's equipment. Location Customer premises. Keywords Elevator, mutual coupling, switching noise. Version date 2004-01-01 System configuration Acoustic noise trouble occurred at a customer premises. The customer complained that the acoustic noise could sometimes be heard; however, it was not clear what the trouble source was. The system configuration of this issue is shown in Figure 1.3-1. At the customer premises, the telecom lines and power mains cable for the elevator (lift) were parallel in the cable duct. The motor of the elevator used a switching power source. The telecom line connected to the telephone set was also connected to the MDF where the power transformer was located. The telecommunication line was changed; however, the acoustic problem continued. MDF Miti(08)_F1.3-1 Figure 1.3-1 – System configuration Copyright © ITU 2010 – All Rights Reserved