There are thousands of electrical projects going on each year in the United States and the vast majority of all commercial and industrial construction will encounter a unique and special piece of electrical equipment called a Transformer. Transformers are used to “Step-Up or Step Down” the voltage to usable levels for a specific task.
Transformers perform the unique task of taking utility voltages, such as 2,300V, 4,160V, 13,800V, 14,400V or even higher, and stepping it down to the typical user level voltages, such as 480V, 277V, 240V, 208V and 120V which we encounter on commercial and industrial electrical installations. The typical voltages experienced in residential electrical installations are 240V and 120V.
Transformers come in a wide variety or types from Delta-Wye, Wye-Wye, Delta-Delta and so on. Some even come in formats that provide a specific single power leg that is considered a High-Leg due to it’s increased voltage reading to a grounded “neutral” conductor. However, that is beyond the scope of this brief explanation. So, what is a delta and what is a wye? The term “Delta” is Greek and is expressed in the electrical industry as a triangle. The 3-phase Delta transformer windings are typically made up of three individual single-phase transformers configured in a delta (triangle) configuration. The term “Wye” is Greek also and is expressed in the electrical industry as a letter “Y”. The 3-phase “Wye” transformer windings are typically made up of three single-phase transformers as well but are configured in a “Y” format where the center of a common connection to all of the individual transformers. The various configurations are what determine the actual voltage the user desires to achieve.
How are transformers used by the utility different than those used in commercial and industrial electrical installations? Well, they are both exactly the same with respect to how they perform the voltage transformation process. However, the voltages typically encountered on the utility side of the installation are much higher voltages to transform. However, that is not always the case. It is important to note that transformers are usually designed as either Liquid Filled or Dry Type. The liquid filled is exactly as it sounds; usually contain a nontoxic oil or coolant that removes excess heat from the inner core to help maintain the life and efficiency of the transformer. The most common transformer experienced on commercial and industrial electrical installations are the Dry Type transformers. These transformers are lighter than oil filled transformers, highly efficient in the utilization of air circulation, which requires proper ventilation and placement clearances. In some cases larger transformers contain an air movement systems, such as circulating fans. In all cases, the installer must adhere to the strictest guidance of the National Electrical Code® and the very detailed installation instructions provided by the transformer manufacturer.
What role does choosing the proper electrical wire-type conductor play in a safe, reliable and code compliant installation of a transformer? The conductors are vital in the operation of a transformer; it brings the power to and from the transformer. The proper sizing of these conductors ensures the maximum permitted use of the transformers is achieved without putting the building at risk. If the conductors are improperly sized the eventual failure of the transformer, the conductors or worse the lowered expectation of the client is all at risk and that is never a good thing.
When installing electrical conductors in an ambient temperature that may result in the ambient exceeding the temperature ratings on the conductors, the end user has to perform a variety of detailed calculations found in the NEC® to offset that condition of use. Assuming this has been taken into consideration the typical wire of choice is Encore Wire’s THHN/THWN-2 conductors. These extremely capable thermoplastic insulated conductors are rated for 90°C for their thermal exposure but in terms of ampacity they are governed by terminal limitations found in section 110.14(C) of the NEC®, as well as per Table 310.15(B)(16). Another fantastic choice would be Encore Wire’s XHHW-2 conductors. These amazing thermoset type cross-linked polyethylene insulated conductors offer the same thermal ratings (90°C), ampacity and terminal limitations as THHN/THWN-2 yet can provide enhanced performance where heat or cold exposure is a concern or other environmental factors exist. Another relevant fact to know is that Encore Wire was the first in the United States to offer XHHW-2 in a 1000V rating without the need for thicker insulation. XHHW-2 is perfect for those situations where the expected voltage levels could creep up over the traditional 600V levels, such as with Photovoltaic Systems, Variable Frequency Drives and Wind Generation Systems.
Ultimately choosing the right electrical wire-type conductor for the job makes all the difference to the life and reliability of the transformer installation. As the Manager of Codes and Standards my effort as part of the Encore Wire Team of Professionals is to ensure our products are safe and standard compliant for everyone.
Paul W. Abernathy, CMI®, CMECP®
Manager of Codes and Standards