Application Note: ACGRID
Revision: 121615
CPS 3Phs String Inverter Compatible AC Connections
This Application Note describes the compatibility of 3-Phase transformer winding configurations, and the neutral
connection requirements associated with the CPS SCA14KTL-DO/US-208, CPS SCA20KTL-DO/US-480, SCA23KTLDO/US-480, CPS SCA28KTL-DO/US-480, and CPS SCA36KTL-DO/US inverters.
The CPS SCA20KTL-DO/US-480 and CPS SCA36KTL-DO/US-480 inverters are designed to be installed as either 3wire or 4-wire systems. Termination or connection of the neutral conductor from the utility interconnect is
optional.
The CPS SCA14KTL-DO/US-208, SCA23KTL-DO/US-480, and SCA28KTL-DO/US-480 inverters are designed to be
installed as four-wire systems. As required by their UL 1741 listing, a neutral conductor from the utilityinterconnect must be terminated at the Neutral terminal within the AC wiring box to ensure that the AC voltage
sensing circuit can perform an individual phase voltage (line-to-neutral) measurement.
The function of the neutral connection is to provide a point of reference for measurement purposes that is
essentially at ground potential. The neutral conductor is for control or measurement purposes only. No power
will flow through the neutral conductor, and as such may be downsized to a 14AWG wire to save wire costs.
There are a many different 3-Phase transformer winding configurations found in commercial and utility scale
service distribution. The following tables illustrate the various types of 3-Phase transformer winding
configurations and compatibility with CPS 3-Phase String Inverters.
Common 3-Phase Transformer Wye Primary Winding Configurations
Transformer Winding
Configuration
Wye Primary w/Neutral Grounded
3Phs + N + PE
Wye Primary w/Shield Grounded
3Phs + N + PE
A
A
L1
L2
L3
N
PE
Inverter Model
SCA14KTL-DO/US-208
SCA20KTL-DO/US-480
SCA23KTL-DO/US-480
SCA28KTL-DO/US-480
SCA36KTL-DO/US-480
L1
L2
L3
N
PE
B
C
N
PE
Compatible (Neutral Required)
Compatible (Neutral Optional)
Compatible (Neutral Required)
Compatible (Neutral Required)
Compatible (Neutral Optional)
B
C
N
PE
Compatible (Neutral Required)
Compatible (Neutral Optional)
Compatible (Neutral Required)
Compatible (Neutral Required)
Compatible (Neutral Optional)
Page 1 of 2
CPS_InvXfmrCompat_121615
Chint Power Systems America
Common 3-Phase Transformer Delta Primary Winding Configurations
Transformer Winding
Configuration
Delta Primary
3Phs + PE
Delta Primary w/Shield Grounded
3Phs + PE
A
L1
L2
L3
N
PE
A
L1
L2
L3
N
PE
B
C
PE
Inverter Model
SCA14KTL-DO/US-208
SCA20KTL-DO/US-480
SCA23KTL-DO/US-480
SCA28KTL-DO/US-480
SCA36KTL-DO/US-480
B
C
PE
Not Compatible
Compatible
Not Compatible
Not Compatible
Compatible
Not Compatible
Compatible
Not Compatible
Not Compatible
Compatible
Uncommon 3-Phase Transformer Delta Primary Winding Configurations
Transformer Winding
Configuration
Delta Primary w/Corner Grounded
3Phs + PE
Open Delta Primary
3Phs + PE
A
L1
L2
L3
N
PE
A
L1
L2
L3
N
PE
B
C
PE
Inverter Model
SCA14KTL-DO/US-208
SCA20KTL-DO/US-480
SCA23KTL-DO/US-480
SCA28KTL-DO/US-480
SCA36KTL-DO/US-480
B
C
PE
Not Compatible
Not Compatible
Not Compatible
Not Compatible
Compatible
Not Compatible
Not Compatible
Not Compatible
Not Compatible
Not Compatible
Page 2 of 2
CPS_InvXfmrCompat_121615
Chint Power Systems America