Heat Pump Wiring Concepts and Diagrams

If you have found this site, chances are you are looking for wiring diagrams. Wiring diagrams are always published by the manufacturer and so the best source to get them is from the manufacturer. Usually they come with the owner's manual, but always should be attached to the door of the electrical panel.

Below are some sample wiring diagrams from a few common manufacturers.

Most heat pump wiring diagrams follow the same concept. So if you are looking to understand the concepts, the diagrams below will help.

Power Wiring

Heat pump wiring is subdivided into two sections:

  • Power wiring
  • Control wiring

Power wiring uses high voltage. Most of it is factory-wired...so it is not too complicated. Follow all local and national electrical code when preparing and installing the wiring and over-current protection.

UL 1995 is a standard developed by UL that most HVAC manufacturers follow. In fact, even if the unit is not UL listed (may have other listings like CSA, TUV, etc.) the manufacturer should have followed UL 1995.

UL 1995 contains two very important calculations. These calculations are essential to understand when design any heat pump electrical system:

  • MCA - minimum circuit ampacity
  • MOP - maximum over-current protection


This number is a guide determining what size power wire to use. The calculation goes like this:

MCA = (1.25 x largest motor FLA) + all other electrical load FLAs

Note: FLA (full load amps)


The MOP (maximum over current protection) is the largest fuse or circuit breaker size desired for the application. This calculation is:

MCA = (2.25 x largest motor FLA) + all other electrical load FLAs

Control Wiring

This is probably the most complicated part of the heat pump. Each manufacturer sets up their controls differently. So a technician must become familiar with each manufacturer.

Consult the wiring diagram specific to your heat pump for details on how to wire your unit.

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