Basic Documentation

Page 8 of 9 Siemens Industry, Inc.
Document No. A6V10431169
K. Bypass
1. The bypass shall be furnished and mounted by the drive manufacturer as defined on the VFD schedule.
All VFD with bypass configurations shall be UL Listed as a complete assembly and carry a UL508 label.
2. A complete factory wired and tested bypass system consisting of a drive output and bypass contactor,
along with a mechanical service switch to isolate the drive from the utility power. A door interlocked,
padlockable circuit breaker or main disconnect with drive fuses shall be standard.
3. The bypass enclosure door and VFD enclosure must be mechanically interlocked so that the
disconnecting device must be in the “Off” position before either enclosure may be accessed.
The VFD and bypass package with a main disconnect, shall have a UL listed short circuit rating
(SCCR) of 100,000 Amps, and this rating shall be indicated on the UL data label.
4. Serial communications – the bypass shall be capable of being monitored and/or controlled using serial
communications. On-board communications protocols shall include Modbus RTU; Modbus TCP;
BACnet MS/TP; BACnet IP; Siemens Industry, Inc. FLN (P1); AND Johnson Controls N2.
5. The bypass control shall include a programmable time delay for bypass start to allow motor
magnetic fields to dissipate for safe bypass operation, and the keypad shall indicate that this
time delay is in process.
6. There shall be a keypad adjustment to select manual or automatic transfer bypass.
7. The digital inputs for the system shall accept 24 Vdc. The bypass shall incorporate an internally
sourced power supply and not require an external control power source.
8. There shall be a run permissive circuit for damper or valve control.
9. There shall be a list of conditions which the user can determine when the drive will automatically
transfer to bypass operation.
10. Each bypass enclosure shall incorporate a diagnostic board for troubleshooting the bypass
components.
11. Electronic bypass systems shall provide override capabilities in the event of electronic bypass controller
failure. The drive shall run in bypass and still maintain all safeties.
12. Both Local and Remote bypass control shall be provided. When remote bypass is enabled, the building
automation system shall be able to start and stop the motor for such things as night time shut down.
13. The bypass package shall include the ability for the user to enable interlocked start features that will not
allow the motor to run in drive hand, drive auto or bypass until a confirming end switch or safety has
been closed.
14. User-defined auto bypass feature based on a drive relay shall be included. This will allow the user to
have the motor operated in bypass mode when the drive faults or for purposes selected by the user
through parameterization.
15. User-defined essential service shall be provided that allows a contact closure to operate the motor at
full speed, ignoring all calls to stop.
16. Contactors shall be interlocked to ensure that both the drive output and bypass contactors do not close
simultaneously.