Most variable speed electronic devices,
including the ECM™ operate with a rec-
tified and filtered AC power. As a
result of the power conditioning, the
input current draw is not sinusoidal;
rather, the current is drawn in pulses at
the peaks of the AC voltage. This pul-
sating current includes high frequency
components called harmonics.
Harmonic currents circulate on the
delta side of a Delta-Wye distribution
transformer. On the Wye side of the
transformer, these harmonic currents are
additive on the neutral conductor. A
transformer used in this type of appli-
cation must be sized to carry the output
KVA that will include the KVA due to cir-
culating currents.
Careful design must be provided when
connecting single-phase products to
three-phase systems to avoid potential
problems such as overheating of neu-
tral wiring conductors, connectors, and
transformers. In addition, design con-
sideration must be provided to address
the degradation of power quality by the
creation of wave shape distortion.
In summary, proper consideration must
be given to the power distribution
transformer selection and ground neu-
tral conductor design to accommodate
the 3-phase neutral AMPs shown in the
adjacent table. Specific guidelines are
available from the factory.
NOTES:
1. Min. ΔPs is the static pressure difference across the primary air valve with the damper
wide open. All downstream losses (including optional hot water coil) are handled
by the unit fan and need not be considered for primary air performance calcula-
tions. Data is certified in accordance with the ARI 880 certification program.
2. NC values calculated based upon the 2002 Addendum to ARI Standard 885
Appendix E Typical Sound Attenuation Values (shown at right).
3. Calculate wire feeder size and maximum overcurrent protective device per NEC and
local code requirements. Recommended fuse type shall be UL Class RK5, J, CC or
other motor rated fuse.
4. Neutral harmonic current contribution for each 3-phase balanced load of motors
at full speed.
5. Includes factory provided 2mH choke for power factor correction.