Products / Rack Mount STS
Rack-mount static transfer switches
A rack-mount STS installs in the same 19-inch rack as the equipment it protects. It takes the A and B feeds already at the rack and moves single-corded loads between them as fast as a quarter cycle. TwinSource, based in Batesville, Indiana, has built them since 2001.
static switches, single and three phase
of rack space
as fast as, per phase
Why put the switch in the rack
A transfer switch protects against everything upstream of it and nothing downstream. Put it in the rack and "upstream" includes the UPS, the PDU, the panel, the breaker, the whip and the technician who opens the wrong one. If the switch itself ever fails, the exposure is one rack, where a large central switch would take a whole row with it.
It is also the practical choice. There is no new conduit, because both feeds are already there. The switch moves with the equipment when the floor plan changes. And one switch turns every single-corded device in the rack into a dual-corded one, which costs far less than duplicating servers and the power and cooling that go with them.
Choosing within the range
What sets them apart
- 100% continuous ratings. A 50 A switch carries 50 A, all day.
- A bypass on every static model, so the electronics can be serviced with the load running.
- Two-pole and four-pole designs that switch the neutral and keep separately derived UPS systems separate.
- Break-before-make transfers at any phase angle, because a failing UPS does not stay synchronized.
- Alarm contacts and RS-485 for DCIM and BMS.
- More than 70 million hours online across the installed base without dropping a load.
Models in this category
| Model | Type | Phase and poles | Voltage | Current | Transfer |
|---|---|---|---|---|---|
| DCC-II | STS | Single-phase 2-pole | 100–240 V | 30–50 A | As fast as ¼ cycle |
| DCC-III | STS | Three-phase 4-pole | 208/120 V | 50 A | As fast as ¼ cycle |
| DCC-4-R | STS | Three-phase 3 or 4-pole, or single-phase 2-pole | 100–480 V | 10–60 A three phase, 10–100 A single phase | As fast as ¼ cycle |
| DCC-4-R4 | STS | Three-phase 3 or 4-pole, or single-phase 2-pole | 100–480 V | 80–120 A three phase, 120–200 A single phase | As fast as ¼ cycle |
| DCC-I | ATS | Single-phase 2-pole | 100–240 V | 12–24 A | < ½ cycle |
Where they are used
Go deeper
Questions engineers ask
What is a rack-mount static transfer switch?
An SCR-based automatic switch in a 19-inch rack chassis. It takes two independent AC feeds and supplies one output, transferring between them in a few milliseconds so single-corded equipment never sees a source failure.
How much rack space does it need?
The DCC-I is 1U. The DCC-II and DCC-III are 4U, which includes the bypass isolation switch and the plug-in electronic module. See the datasheet for DCC-4-R heights.
How is this different from a rack ATS or a PDU with a built-in ATS?
Those use relays. A static switch uses SCRs: no contacts to bounce or wear, higher current, full rating at real power factors, out-of-phase transfers, and a bypass for maintenance.
Can it feed my rack PDU?
Yes. The output feeds the rack power strip or PDU, and everything plugged into it gains a second source.
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