Rheem 953060DP Owner's Manual And Installation Instructions page 57

Auxiliary Boost Element
Depending on the installation, an auxiliary boost element may be supplied with
an RT or RW series storage tank.
An auxiliary boost electric heating element may be interlocked with the heat
pump. Both Voltage Free (VF) and 230V terminals are supplied within the heat
pump electrical enclosure.
These can be used as required for interlocking auxiliary boost with heat pump
operation.
Operation of auxiliary boost will occur under two (2) situations:
•
If the ambient temperature drops below the designated set point
•
If more than 50% of the compressors (within one heat pump) are
in fault.
For 230V operation, connect to the terminals marked 'SA', 'N' and 'E' in the heat
pump enclosure. Maximum current is 1A.
Picture of heat pump terminal strip
57