HVAC: Not Just Your Average Load

The topic of heating, ventilation, and air conditioning (HVAC) presents a target-rich environment with regard to the topic of safety. As installers, we may only be concerned with the tools, personal protective equipment, liquids and chemicals, and electrical hazards from a safety perspective. We have to also consider that HVAC equipment could play an important role throughout its life for the contents (including people and goods) of the structure or area it serves. The fact that HVAC systems account for 39 percent of the energy used in commercial buildings in the United States means that we probably see a lot of these types of applications.

For many reasons, the most important day in the life of HVAC equipment is the day it is installed. The selection and installation of HVAC equipment is surrounded with parameters that must be considered that go beyond heating and cooling to the electrical supply equipment. The system must perform to the expectations of the design and do so for a long time without experiencing issues outside of normal maintenance concerns. The use of listed products for not only the HVAC equipment itself but for all of those components used in the installation help the system perform safely. It’s important that the equipment is installed per their listing requirements/ manufacturer instructions. The installer can be presented with a challenge when trying to determine the proper size of overcurrent protective devices and/or proper short circuit current ratings for this equipment. It’s the installer, for the most part, that must deal with the details.

An important section of the UL White Book (www.ul.com/whitebook) is in Appendix A, “UL Marking Guide,” which includes a marking guide for “Electric Heating and Cooling Equipment.” This marking guide can be useful to the installer as it describes all of the marks required by UL for the equipment. This reference helps us understand nameplates for this equipment, which can be confusing. For example HVAC equipment can be quite complex with voltage ratings that vary. Voltage ratings can be a single nominal value such as 230V or a ranges expressed as “220 – 240.” Standard voltage ranges include110—120, 200—208, 220—240,254—277, 440—480, and 550—600. A single unit may have more than one voltage rating because more than one supply circuit can be connected. A unit with more than one supply circuit will probably have different load ratings for each circuit. This is important for sizing overcurrent protective devices, conductors, and even generators should one be used to supply this load along with others.

Per UL 1995, the HVAC nameplate can specify the type of overcurrent protective device that must be used. When the nameplate specifies “Maximum Overcurrent Protective Device,” then either a circuit breaker or fuse is permitted. If the nameplate is marked “Maximum Fuse_____,” then fuse protection must be provided in accordance with the label. If the nameplate is marked “Maximum Circuit Breaker_____,” a circuit breaker must be provided in accordance with the label. Sometimes the equipment makes life easy for the installer/inspector.

Reading nameplates can be challenging. The UL Marking guide can help interpret what you are seeing. As always there is the call to the manufacturer that should be made if needed.

NEC REQUIREMENTS

HVAC equipment must get power from some electrical source and how that occurs is directly impacted by the National Electrical Code® (NEC®). The following are some key articles important to the successful application of HVAC equipment:

  • Article 110, “Requirements for Electrical Installations”
  • Article 210, “Branch Circuits”
  • Article 220, “Branch-Circuit, Feeder, and Service Calculations”
  • Article 240, “