Bryant Durapac Plus Series 551a User Manual
Page 10
—
10
—
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