Can HVAC Unit Heat Strips Be Changed in the Field?

Occasionally large projects run into problems, such as building electrical requirements exceeding the power available at the site, or an original bid including an undersized main distribution panel, or undersized site switch gear.

One of the first places planners look to solve these problems is the HVAC system, especially if the HVAC units include heat strips for primary or secondary heating. Let's look at why, and some possible solutions; first, some background on heat strip testing per UL listing standard, then what options are available to change heat strips in the field.

If HVAC equipment manufacturers had a choice, they would eliminate heat strips from HVAC units altogether because of the extensive test procedures involved with the process.

Heat strip testing involves monitoring hundreds of thermocouples during normal and abnormal operating modes to ensure that excessive duct or unit temperatures are not created. This testing must meet or exceed current UL requirements.

HVAC equipment manufacturers submit to UL the different sizes (KW) of heat strips for use in their units. This could be literally any size, but usually nominal increments of 5 KW (5, 10, 15, 20) are selected in single and three phase. Next the HVAC equipment manufacturer decides to submit the heat strip package to UL as a factory-built-in package only, a field-installed package only, or a factory/field-installed heat strip package.

If the HVAC equipment manufacturer has submitted their units to UL for factory/field installation, you are allowed to select and change in the field the heat strip package to larger KW (more amperage) for more heat, or smaller KW (less amperage) for less heat. However you must use the heat strip package as provided by the HVAC equipment manufacturer and as listed by UL. Otherwise adding, removing, or modifying heat strip package wires, parts, or the heat strip itself violates the UL listing and has tremendous liability associated with it.

Increasing a heat strip package KW will require a larger circuit breaker and wire size. Reducing the heat strip package KW does not necessarily require a change to smaller wire, but will require a properly sized (smaller) circuit breaker. Electrical inspectors are required to follow the circuit breaker and wire size listed on the data/serial plate for switch gear sizing.

At no time should anyone ever clip, or disconnect the wires on a heat strip to disable half or a portion of it's capacity.

1.	This violates the UL listing.
2.	Liability for fires and electrocution falls on those who cut/disconnected the heat strip.
3.	Required review and change out of the heater limit or TCO switch, a Serious Risk Issue.
4.	Limit control protection varies depending on what was cut/disabled, a Serious Risk Issue.

HVAC equipment manufacturers with factory-only heater packages put data/serial plates on their units, which clearly identify the heat strip KW size, wire size, and amperage. Only a few HVAC units with a factory-only installed heater package have the option of a single point field wiring kit. Most HVAC units with a field-only installed heater package require two field circuits: one for the unit, one for the heater package. Very few equipment manufacturers have a single point wiring kit for field installed heater packages. Two field wiring circuits is the norm.

HVAC equipment manufacturers with a factory/field installed heater package must also provide a means of marking the unit data/serial plate to comply with the UL listing. It is important that the data/serial plate be properly changed according to the manufacturers installation instructions and UL listing.

So yes, HVAC unit heat strips may be changed in the field, as long as the HVAC unit and heat strip package are UL listed to do so, and appropriate procedures are followed.

Which now brings us back to the challenges faced on projects with the building electrical load exceeding what the end user has on site, and how this relates to the HVAC equipment. We have seen how the use of heat strips impacts the KW and wire size. A look at amperage is important also for electrical load planning.

During the initial discussion with the End User, the dealer should ask how much amperage is available at the site, or estimate for the end user what the requirement may be. All too often on complex projects, the End User and/or Dealer do not obtain this information soon enough to prevent site problems or costly project redesigning. Having some basic information up front about building electrical loads is critical.

Simply multiply the number of modules times the selected HVAC unit above to get an idea of the total building HVAC load. If the building is zoned and larger units are used, the total could be less, but that takes further review of the project to determine. Then add in the requirement of all other electrical loads such as lighting, water heaters, receptacles, etc.

To avoid facing the major problem of "too much building, not enough power", and the associated concern of "illegal" removal, cutting, or disconnecting heater packages later on, simply pre-calculate the electrical load for the project. Many building manufacturers will pre-calculate the electrical load for the Dealer/End User when some basic information is available to determine HVAC unit size on a project.

Contact your building manufacturer, mechanical engineer, or equipment supplier with the size of the site amperage available at the beginning of your next project. Your review of the electrical load of the project up front will save time and money for all involved. If you find that you have electrical loads on site greater than the switch gear or amperage available, remember to refer to the manufacturers installation instructions and UL listing to avoid costly risk and liability.

Stay fully powered until the next time we meet in . . . The Comfort Zone.