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Hardwiring to 120v, 208v, and 240v loads from a 208v/240v SmartUPS RT UPS


Issue:

Hardwiring to 120v, 208v, and 240v loads from a 208v/240v SmartUPS RT  UPS

Product Line:

Smart-UPS RT

Environment:

All models with "T" in the suffix of the part number. (IE: SURT3000XLT, SURT8000RMXLT6U)
Note: This does *NOT* include SURTD5000RMXLP3U or SURTD6000RMXLP3U. These two models are split phase 4 wire (Hot/Hot/Neutral/Ground) units and do not require a stepdown transformer to support 120v loads.

Cause:

Smart-UPS RT units designed for 208v/240v environments have unbalanced 3 wire outputs and require a transformer to supply 120v loads.

Resolution:
  • The 208V/240V Smart-UPS RT is a single phase UPS with a 3 wire unbalanced output.
  • They require 2 hots and a ground on the input, and 2 hots and a ground on the output.
  • They do not use a neutral.
  • They require a stepdown transformer to power 120v loads and provide a Neutral

The output of the UPS is unbalanced, meaning that from hot to hot you will see 208 volts (or 240v if so configured), however it is not two balanced 120 volt legs as you would traditionally see from 208v/240v utility power. The two output legs are 180 degrees out of phase and from hot to hot they will measure 208v or 240v. All of these units default to 208v out and can be configured to 240v via the network management card or LCD interface.

Attempting to hardwire out to a 120V load without the use of a transformer will result in load drops and possible load damage!

In addition to a selection of smaller 5kva plug in step-down transformers, APC manufactures 3 larger hardwire step-downs in 10kva and 20kva capacities - APTF10KT01APTF10KW01, and the APTF20KW01
All three of these units create their output in a similar fashion. A neutral is created via a center tap on the transformer.

To supply a 120 v load, the transformer provides:

  • 2 120 volt legs that are 180 degrees out of phase
  • Ground
  • Neutral

This creates a traditional 240 v/120 v panel where there are 2 legs of 120 v and from hot to hot you would measure 240 volts.

To supply a 208 v load, the transformer provides:

  • 120 v Hot Leg
  • 88 v Hot Leg (180 degrees out of phase from the 120 v leg)
  • Ground

In this configuration you would measure 208 volts from Hot to Hot.

For detailed wiring directions, diagrams, and specifications, please consult the users manual for your step-down transformer.

Using both of these configurations you can support both 208v and 120v loads, however you are not able to output to a traditional 208v / 120v panel where there are 2 120v legs that are 120 degrees out of phase. If a 208v / 120v output panel is required you must use one of our split phase solutions. We offer 2 split phase RT units (SURTD5000RMXLP3U and SURTD6000RMXLP3U) as well as the entire Symmetra LX line. A split phase UPS will require a 4 wire input and will output 2 balanced 120 v legs, a ground, and a neutral. The split phase RT units will require the SURT018 hardwire kit to be used in a hardwired application.

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