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LEGEND
*Heater capacity (kW) is based on heater voltage of 208 v, 240 v, and
480 v. Heaters are rated at 240 v, or 480 v. If power distribution volt-
age to unit varies from rated heater voltage, heater kW will vary
accordingly.
†Fuse or HACR circuit breaker.
**Heaters are field installed only.
NOTES:
1. In compliance with NEC requirements for multimotor and combina-
tion load equipment (refer to NEC Articles 430 and 440), the overcur-
rent protective device for the unit shall be fuse or HACR breaker.
Canadian units may be fuse or circuit breaker.
2.
Unbalanced 3-Phase Supply Voltage
Never operate a motor where a phase imbalance in supply voltage is
greater than 2%.
Use the following formula to determine the percent
of voltage imbalance.
% Voltage Imbalance
Example: Supply voltage is 460-3-60.
AB = 452 v
BC = 464 v
AC = 455 v
= 457
Determine maximum deviation from average voltage.
(AB) 457 – 452 = 5 v
(BC) 464 – 457 = 7 v
(AC) 457 – 455 = 2 v
Maximum deviation is 7 v.
Determine percent of voltage imbalance.
% Voltage Imbalance = 100 x
= 1.53%
This amount of phase imbalance is satisfactory as it is below the maxi-
mum allowable 2%.
IMPORTANT:
If the supply voltage phase imbalance is more than 2%,
contact your local electric utility company immediately.
3. MCA calculation for units with electric heaters over 50 kW = (1.25 x
IFM amps) + (1.00 x heater FLA).
Table 3 — Electric Resistance Heater Data
*Maximum number of stages using accessory low-ambient kit or head pressure control device and low-ambient kit.
NOTE:
Heaters are rated at 240, and 480 v.
FLA —
Full Load Amps
HACR—
Heating, Air Conditioning and Refrigeration
IFM —
Indoor (Evaporator) Fan Motor
LRA —
Locked Rotor Amps
MCA —
Minimum Circuit Amps
MOCP—
Maximum Overcurrent Protection
NEC —
National Electrical Code
OFM —
Outdoor (Condenser) Fan Motor
RLA —
Rated Load Amps
= 100 x
max voltage deviation from average voltage
average voltage
Average Voltage =
452 + 464 + 455
3
=
1371
3
7
457
UNIT
551A
HEATER kW
HEATER
STAGES
% HEAT
PER
STAGE
MAXIMUM
STAGES*
MINIMUM
HEATER AMPS
Unit Voltages Heating Cfm
208 230 240 460 480 Cfm L/s 208 230 240 460 480
155
14 17 19 14 15 1 100 1
3750 1770
39.3 43.4 45.3 17.2 17.9
26 31 34 30 32 2 50/50 2 71.3 78.9 82.3 37.3 39.0
42 52 56 50 55 2 33/67 3 117.0 129.4 135.0 63.3 66.1
180
26 31 34 30 32 2 50/50 2
3750 1770
71.3 78.8 82.3 37.3 39.0
42 52 56 50 55 2 33/67 3 117.0 129.4 135.0 63.3 66.1
56 69 75 73 80 2 50/50 4 155.9 172.4 179.9 92.0 96.0
240
26 31 34 30 32 2 50/50 2
5000 2360
71.3 78.8 82.3 37.3 39.0
42 52 56 50 55 2 33/67 3 117.0 129.4 135.0 63.3 66.1
56 69 75 73 80 2 50/50 4 155.9 172.4 179.9 92.0 96.0