Installing a heat pump in your home is an energy-efficient solution for heating and cooling. To ensure a safe and efficient installation, it’s crucial to understand the electrical requirements.
We’ll explore the electrical aspects of heat pump installations, including conductor sizing, breaker sizing, and the National Electrical Code (NEC) guidelines. Let’s dive in!
Key Terms & Principles
To better understand the electrical requirements for heat pumps, it’s essential to familiarize yourself with the key terms and principles involved. The rules for designing heat pump circuits are specified in Article 440 of the National Electrical Code (NEC).
Phase, Frequency, and Voltage
Heat pumps require specific voltage, frequency, and number of phases to operate correctly.
Electric grids in the United States, Canada, and Mexico run at a frequency of 60 Hz, while most grids in Europe, Asia, and Africa run at 50 Hz. In addition, residential electric services utilize only one of the three phases, whereas commercial facilities and some larger multifamily buildings use three-phase power.
Most heat pump systems are rated for 208/230V, meaning they can be installed in buildings with single-phase or three-phase service.
The amount of electrical current flowing through the conductors in a heat pump circuit is measured in amperes (A). Rated amps represent the current drawn by the heat pump under normal operating conditions.
This includes the sum of the compressor, the outdoor unit fan, electronics, the base pan heater (if present), and any indoor units powered by the outdoor unit.
Sizing a Main Electric Service & Breaker Panel
A heat pump’s power requirement, in volt-amperes (VA), is calculated as follows:
VA = Rated Amps x voltage
This calculation is used when sizing a main electric service and breaker panel.
Some heat pump literature may list different rated amps for heating and cooling modes, and both numbers should be entered into the service sizing calculations.
Ensuring Safe & Code-Compliant Installation
For safety reasons, all wiring should be done by a qualified person. All required permits should be obtained before the start of work, and inspections should be performed when the work is complete.
Understanding a heat pump’s electrical specs can also help identify opportunities for cost savings. These may include avoiding oversized conductors, reusing an existing HVAC circuit, and working within the limitations of the existing electric service.
Keep in mind that heat pumps rated for 208/230V can work with single-phase or three-phase electric service. Therefore, testing incoming voltage at the main breaker panel is crucial, and working with the utility to correct high or low voltage if necessary.
In some situations, a “buck-boost” transformer can be installed on the heat pump circuit to bring the voltage within spec.
Finding Heat Pump Electrical Specifications
To determine the electrical requirements for your heat pump, you’ll need to find the specific electrical specifications for your particular model. These specifications can typically be found in the following locations:
- Nameplate: The nameplate is a label or metal plate attached to the heat pump that contains essential information, such as the model number, serial number, and electrical specifications. This label is usually located on the outdoor unit and includes the Minimum Circuit Ampacity (MCA), Maximum Overcurrent Protection (MOCP), and Rated Amps.
- Submittal sheet: The submittal sheet is a document provided by the heat pump manufacturer that contains detailed information about the product, including electrical specifications, performance data, and installation guidelines. You can usually find submittal sheets on the manufacturer’s website or by contacting customer support.
- Installation manual: The installation manual is a document that comes with the heat pump and provides step-by-step instructions for proper installation, electrical requirements, and safety guidelines. This manual typically contains the necessary electrical specifications, such as MCA, MOCP, and Rated Amps.
- Manufacturer’s website: If you need help locating the electrical specifications on the nameplate, submittal sheet, or installation manual, you can often find this information on the manufacturer’s website. Search for your specific heat pump model; the website should provide relevant documents and information.
Always consult the electrical specifications the heat pump manufacturer provides and follow the National Electrical Code (NEC) guidelines to ensure a safe and code-compliant installation.
Minimum Circuit Ampacity (Mca) & Maximum Overcurrent Protection (Mocp)
MCA and MOCP are two essential specifications to consider when determining the suitable conductor and circuit breaker size for a heat pump. The MCA is the minimum size of the conductor required to safely carry the electrical load of the heat pump, while the MOCP is the maximum size of the circuit breaker or fuse that can be used to protect the equipment.
The MCA is typically calculated as 125% of the rated amps, while the MOCP is often calculated as 225% of the rated amps. These percentages may vary depending on the specific heat pump model and manufacturer recommendations.
We’ll go into more detail in each below.
Minimum Circuit Ampacity (Mca)
MCA, or Minimum Circuit Ampacity, is the minimum current rating required for the conductors powering the heat pump. This measurement ensures that the conductors can handle the necessary current without overheating, providing a margin of safety for your system.
To calculate the MCA, you need to add 25% to the compressor’s current draw (RLA) and include the current draw of other components like the fan (FLA) and any additional component loads:
MCA = [Compressor RLA x 1.25] + Fan FLA + Other component loads
Selecting Conductor Size
When selecting conductor size, follow the NEC Table 310.16 guidelines. For instance, use:
- 14-gauge wire for 15A circuits
- 12-gauge wire for 20A circuits
- 10-gauge wire for 30A circuits
Make sure to choose conductors with the appropriate temperature ratings as well. For example, most heat pump terminals are rated for 75C, so select conductors are rated for at least 75C.
Remember that while the MCA dictates the minimum conductor size, you can always opt for larger (lower gauge) conductors as long as they are compatible with the circuit breaker and the heat pump terminal block.
Maximum Overcurrent Protection (Mocp)
MOCP, or Maximum Overcurrent Protection, refers to the maximum circuit breaker current rating allowed for a given heat pump. The circuit breaker serves three main functions:
- De-energizing a circuit for safe maintenance
- Overcurrent protection to prevent conductors from overheating
- Short-circuit protection
To calculate MOCP, use the following formula:
MOCP = [Compressor RLA x 2.25] + Fan FLA + Other component loads
The resulting number should be rounded down to the nearest 5A increment but not lower than the MCA.
Importance Of Mocp
MOCP helps prevent circuit breakers from tripping during the brief inrush of current when older compressors start-up. It specifies the maximum breaker size allowed, but a smaller breaker is permitted, although it may lead to nuisance trips.
Communication & Control Wiring
In typical ductless or compact-ducted heat pumps, the indoor units are powered by the outdoor unit. The cable connecting the two has three current-carrying conductors and a ground.
These conductors must be of specific types and gauges to ensure correct operation. Oversizing communication wires can lead to system malfunction.
Manufacturers like LG and Mitsubishi recommend using 14-gauge stranded communication wire or 16-gauge for specific applications. In addition, shielded control wires are recommended in some situations to prevent interference from household electronics.
Supplemental Heat Circuits
Fully ducted air handlers often include resistance heaters, or “heat strips,” which provide supplemental heat in cold weather and during the defrost cycle. These heaters ensure comfort and can serve as an emergency heat source if the outdoor unit fails.
Sizing Heat Strip Circuits
Resistance heaters require a dedicated circuit, and the conductor and breaker sizing depends on their power rating (in kW). You can find this information in the heat strip’s submittal.
If the air handler is not in direct line of sight of the electrical panel, the heat strips will need a switch or disconnect.
Conductor Temperature Ratings
When selecting conductors for heat pump installations, it’s essential to consider their temperature ratings.
The National Electrical Code (NEC) Table 310.16 provides guidance on conductor sizing based on ampacity ratings for copper conductors and terminals with temperature ratings of 60C (140F), 75C (167F), and 90C (194F).
The terminals in heat pumps, disconnects, and circuit breakers are rated at 75C. Therefore, if you select conductors rated for at least 75C, you can size your conductors using the 75C column in Table 310.16. This could save money by allowing smaller conductors or reusing an existing circuit that might otherwise appear undersized according to the 60C ratings.
Remember that the ampacity ratings in Table 310.16 are based on specific assumptions, such as no more than three current-carrying conductors in a raceway and an ambient temperature no higher than 30C (86F).
If these conditions do not apply, the NEC provides adjustments to ensure the chosen conductors are suitable for the environment in which they are used.
Voltage Drop Considerations
When installing a heat pump more than 100 feet from the breaker panel, it may be necessary to increase the conductor size to avoid excessive voltage drop.
Voltage drop occurs when the voltage at the end of a conductor is lower than the voltage at the beginning due to resistance in the conductor.
Excessive voltage drop can cause inefficient operation and potential damage to the heat pump. To prevent this, choosing the appropriate conductor size is essential to maintain a safe and consistent voltage supply.
Types Of Electrical Conductors
Various types of electrical conductors are used in heat pump installations, including:
- THHN wire in flexible conduit
- Solid copper wire with nonmetallic sheathing (e.g., “Romex”)
- Stranded communication cable
- Stranded, shielded wire (used with some wired controllers)
Each conductor type serves a specific purpose and offers unique benefits. For instance, a stranded communication cable is recommended for indoor and outdoor heat pump units to facilitate proper communication between the units. Likewise, shielded control wires can be advantageous in situations where household electronics might interfere with low-voltage control signals.
When selecting electrical conductors for your heat pump installation, always follow the NEC guidelines and manufacturer recommendations to ensure a safe and efficient system.
Impact Of Local Weather Conditions
Local weather conditions can affect the performance of heat pumps and their electrical requirements.
In areas with extreme temperature fluctuations, ensuring the heat pump can handle the increased electrical load during peak usage times is essential.
Choose a bigger heat pump or add more equipment, like a second heat source, to ensure your space is heated and cooled enough. Alternatively, manufacturers do sell cold-climate heat pumps which may be an excellent solution.
Importance Of Proper Maintenance
Taking care of your heat pump system by cleaning its filters and checking its electrical connections regularly can make it work better and last longer.
It is essential to follow the manufacturer’s recommendations for maintenance to ensure optimal performance and minimize potential issues related to electrical requirements.
Rebates and Incentives
When considering the installation of a heat pump, it’s worth researching available rebates and incentives from local utilities and state and federal programs.
These incentives can offset the heat pump and installation cost, making it more affordable and encouraging the use of energy-efficient heating and cooling solutions.
Understanding and following the electrical requirements for heat pump installations is crucial for ensuring a safe and code-compliant setup. By adhering to the guidelines in this guide, you can successfully size conductors and breakers and choose the appropriate communication and control wiring for your heat pump system.
Remember that the MCA determines the minimum conductor sizing, while MOCP determines the maximum breaker size allowed. Always follow the NEC guidelines and manufacturer recommendations to ensure a safe and efficient installation.
Proper planning and adherence to these electrical requirements make your heat pump a reliable and energy-efficient addition to your home.
Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.