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Temporary Wye-Wye 120/208V 4-Wire Bank for Limited Phase Wires

This bank is used to supply a 3-phase 4-wire service of 120/208 volts when only two different phase wires are available. It involves connecting transformers in a specific configuration and taking special precautions. This connection is not very efficient but useful in temporary or emergency applications.

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Temporary Wye-Wye 120/208V 4-Wire Bank for Limited Phase Wires

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  1. Open Wye-Wye 120/208 4 wire

  2. This bank is used to supply a three phase four wire service of 120/208 volts when only two different phase wires are available. One of the transformers will need to be twice the KVA capacity as the others as it will have full line current on both coils. The tank straps connected to the smaller transformers X2 bushings will need to be removed. One of the X2’s will become a secondary phase wire. The other is removed to prevent secondary neutral current from flowing on the case grounding system. This connection is not a very efficient use of transformers but is useful in a temporary application or emergency.

  3. OSHA Required Tailgate Discussion Topics • Hazards Associate with the job • Work Procedures Involved • Special Precautions • Energy Source Controls • PPE Required

  4. Special Precautions Work Procedures Involved Hazards associated with the job Energy Source Controls Personal Protective Equipment Be sure to record your emergency location and post in a location everyone on the crew knows. Have your PPE and First Aid kit available Be sure your AED is accessible. A safe job begins with a thorough inspection of… Tools Be certain all of your tools are in good shape. Equipment Make sure your trucks are all in working order take time to preflight your equipment and insure there are no surprise. Line/Structure Look over the line and structure. Are there any potential hazards? (Broken insulators, damaged wire, clearances over roads or from trees?) Be aware of your work area, be sure to cover anything you can reach touch or fall into. And anything that can reach touch or fall into you! Discuss all PPE needed for the job and wear your PPE. Be sure to inspect your equipment prior to use. Identify all voltages you are exposed to. Be sure to have all of your Arc-Flash protective gear on. Identify a dedicated observer Working in traffic exposes you to hazards that are difficult to control. Give the vehicles plenty of time to see and avoid you! Follow the manual of traffic control for your area. Slips trips and falls are some of the most common injuries, look for hazards that could cause this. Be sure to inspect and wear your fall arrest harness.

  5. Hang the required hardware Note the side that has two cutouts is opposite the system neutral. You only need two cutouts.

  6. Parallel two of the transformers internally. Leave one series internally. This transformer will need to be twice the KVA as the others. Ground all of the transformer cases as well as the transformer cluster.

  7. Remove the tank strap from the X2 bushing of the smaller left and center transformers. X2 Remove tank strap

  8. Connect all primary H2 bushings together and then connect them to the system neutral. H2

  9. Connect all primary H1 bushings of the center and left transformers to the left cutout. H1

  10. Connect all primary H1 bushings of the right side transformers to the cutout. H1

  11. Connect the center transformers X2 and the larger right hand transformers X2 together and then to the service neutral. X2 X2 Neutral

  12. Connect the Larger right hand transformers X3 to the far left transformers X1. This wire should be isolated from everything else. X3 X1 Neutral

  13. Connect one of the service lines to the left transformers ungrounded X2 bushing. X2 Neutral Line

  14. Connect one of the service lines to the center transformers X1 bushing. X1 Neutral Line

  15. Connect one of the service lines to the larger right hand transformers X1 bushing. X1 Neutral Line

  16. With the cutouts open, connect the primary jumpers to different phases. Neutral Line

  17. Close the cutouts, test voltage and rotation. Neutral Line

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