Heat Pump Wiring Concepts and Diagrams


If you have found this site, chances are you are looking for heat pump 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 generally 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 Goodman wiring diagram is a good place to start.



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



MCA (Minimum Circuit Ampacity)

Ampacity essentially refers to wire amp capacity.  Wiring is rated by ampacity and therefore it is important to calculate minimum ampacity of a specific branch as more than just the sum of all full load amps downstream of the wiring.  The calculation goes like this:

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

Note: FLA (full load amps)

Wiring can handle instantaneous amp spikes (such as when a motor starts).  So 25% above the largest motor amp draw plus the sum of the remaining load amps is sufficient for wiring size.  Manufacturers will often specify the MCA in their literature because internal to the unit could be multiple sources of full load amp draw (compressor(s), condenser fan(s), electric heater, etc).



MOP (Maximum Overcurrent Protection)

The MOP 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

Much like MCA, MOP is often published by the manufacturer.



Control Heat Pump 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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