Low Voltage Transformer Application

This course will give the student a foundation to handle many transformer applications regardless of the size of the transformer.  Two transformers will be used as our example including a 75kVA and 500kVA transformer.  The student will understand when Article 450 applies and when it does not.  A review of various areas of the NEC will give the students skills necessary for many different applications that require navigating NEC requirements.

NEC Areas that will be explored and understood include the following:

Article 215 Feeders: Conductors on primary and secondary of the transformer are feeders and the requirements of Article 215 apply.  This article will help determine the minimum conductor ampacity but essentially points the user to Article 240 for proper conductor protection.  the section discussed here includes 215.3 but as you'll see, we do provide a short-cut and the reason why the short-cut is appropriate to a transformer application.

• 215.3 Overcurrent Protection.

Article 240 Overcurrent Protection: Includes important requirements that directly apply to transformer secondary conductors.  A transformer secondary presents a unique situation in that the overcurrent protection for that conductor is not located at the source of the secondary conductor.  This program will help you navigate the NEC to ensure proper protection of not only the transformer but also the transformer conductors. 

• 240.4 Protection of Conductors.

  (F) Transformer Secondary Conductors.

Article 408 Switchboards, Switchgear, and Panelboards: Will be important when supplying this equipment directly from a transformer.  The requirements here especially for panel boards is often missed by design engineers and installers.  We'll understand why in many applications, we will be required to place a secondary OCPD on the transformer and the reason may not be what you expect.

• 408.36 Overcurrent Protection.

  (B) Supplied Through a Transformer.

Article 450 Transformers and Transformer Vaults (Including Secondary Ties): Critical Article for all things transformers but for this curriculum we will focus on the overcurrent protection for the transformer.

• 450.3 Overcurrent Protection.

  (A) Transformers Over 1000 Volts, Nominal.

  (B) Transformers 1000 Volts, Nominal, or Less.

This course will provide a foundation for proper transformer protection and give the attendee a foundation to understand how to navigate the National Electrical Code.  Proper transformer protection begins during the design phase.  Throughout this course, the instructor will provide tricks of the trade and advice on how to ensure a solid design that will have minimal changes once equipment is purchased and installed.  This course will also provide a foundation to address existing installations to ensure the continued protection of installed transformers and related equipment.