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"Preplanning a transformer installation is critical. Make sure you have all of the materials, tools and equipment your crew will need available and in place before the work begins"

Installation and Inspection of Dry Type Transformers       3

Written by Ted "Smitty" Smith  2017
Excerpts Copied from Eaton Reference Material

Transformers need to be installed with adequate clearances both based on working clearances from Table 110.26 of the NEC and also based on manufacturers requirements. 
Before installing a transformer it is important for you to read the manufacturers instructions. Here are the specific items you need to know:
  • What are the clearances required by the manufacturer.?
  • What types of shipping braces or bolts are in the transformer and how do they need to be placed for operation?
  • What is the weight of the transformer?
  • Are there any specific mounting instructions. 
  • What are the torque requirements and values for both mounting hardware and terminations?

TABLE 110.26(A)(1) of the NEC defines working clearances for all electrical equipment. Working space is required so that electricians can safely maintenance electrical equipment after installation. 
Be sure to read Article 110. 26 and refresh your memory of the working clearance requirements before installing a transformer. Be sure to remember the following:
  • Measurement from exposed live parts is done from the face of the cover over the exposed live parts, not from the actual exposed live parts
  • The working area extends from the floor to the top of the equipment, and the entire width of the equipment or 30" whichever is greater
  • A grounded part is anything that is connected to ground, such as a run of conduit, another piece of electrical equipment, a light switch, receptacle or structural steel.
  • Concrete floors, ceilings or walls are considered to be grounded.
  • Also, remember that most transformers  CAN NOT be placed below electrical panels because they are in the working clearance of that panel and they will stick out farther than 6" beyond the face of the panel they are mounted below.  

Due to working space restrictions or ventilation clearances, transformers very often have to be hung above other electrical equipment. When mounting a panel above other electrical equipment, you will need to build a Unistrut rack to support the transformer. Be sure to know the weight of your transformer and design the Unistrut rack and the anchors for the Unistrut rack to handle a minimum of 150% of the actual transformer to ensure the transformer is adequately and safely supported. I recommend submitting an RFI with your mounting design to the electrical engineer for approval. 

Once the transformer is in place you can begin the process of installing the electrical system.
Some key things to remember when wiring the transformer:
1.  Be sure to read the installation manual or look on the inside of the cover and find the torque values for all the terminations. Be sure to use a calibrated torque wrench to make your terminations.  And make a torque termination inspection report with iAuditor and send it to your project coordinator for filing in the project file. 
2. Do not bring electrical raceways into the transformer through any ventilation openings. 
3. Ensure you use a flexible raceway for both the primary and secondary wiring due to vibration. 
4. Grounding and bonding must be done on a single terminal lug or terminal bar in a dry type transformer. 450.10(A) Determine the number of terminations will need to be made and include the system bonding jumper from the X0 terminal, all bonding jumpers, grounding electrode conductors and equipment grounding conductors. Order a multiple termination lug large enough to accept all of these conductors. 
5. Be sure to not block ventilation openings
6. Double check to make sure that all multiple tap connections are made to the same termination on each of three coils. 
7. Always double check the enclosure to make sure no tools or parts are left in the enclosure after finishing the wiring. 
8. Clean out the enclosure.