Installing a TwinSource transfer switch

• Confirm the two sources are independent. Two circuits from the same panel protect against very little. Feed the switch from different PDUs or panels, ideally from different UPS systems.
• Confirm voltage, frequency and pole count against the nameplate, and that the rating covers the load with margin.
• Size each feeder breaker and its conductors to your electrical code and the operating manual for the model.
• Check that the available fault current at the installation point does not exceed the fault rating on the nameplate.
• Allow rack space and airflow: 1U for the DCC-I, 2U for the DCC-4-R, 4U for the DCC-II, DCC-III and DCC-4-R4. Use a rack shelf and cable strain relief where a unit’s weight exceeds the two-post mounting capacity of the rack.

1. Mount the unitRack-mount models fit a standard 19-inch rack. Wall-mount cabinets need a surface rated for the weight, with clearance for the door and the bypass handle.
2. Connect the groundConnect the equipment grounding conductor to the switch's ground terminal first, before any source or output wiring.
3. Connect source 1 and source 2Land each source on its own input. Keep A and B cabling separated and labelled from the breaker to the switch.
4. Connect the outputFeed the rack power strip, the load panel or the equipment directly. Moving the equipment later means moving the switch with it, and nothing else.
5. NeutralThe switch transfers the neutral with the phases on 2-pole and 4-pole models. Do not bond the two source neutrals together anywhere downstream.
6. Connect monitoringWire the alarm contacts to your BMS, DCIM or RTU, and RS-485 where it is used.
7. Energize and verifyClose source 1, then source 2. Both "available" indicators should light. Select the preferred source.
8. Test the transferWith the load connected, open the preferred source breaker. The load should stay up, the indicators should show the alternate source, and the alarm should reach your monitoring system. Restore the source and confirm the retransfer.
9. Test the bypass and documentWalk through the bypass sequence in the manual once while everyone is watching. Update the one-line diagram and label the rack.

General guidance only. Installation must be carried out by qualified personnel, to the operating manual and your local electrical code.