Bryant 549B - Manual (Page 9)

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LEGEND AND NOTES FOR TABLES 3A-3D
LEGEND
*Heaters are field installed only.
†Minimum unit disconnect size is used to determine minimum discon-
nect per NEC.
**Heater capacity (kW) is based on heater voltage of 208 v, 240 v,
480 v. If power distribution voltage to unit varies from rated heater
voltage, heater kW will vary accordingly.
††Fuse or HACR circuit breaker.
***Factory-installed disconnect is not available for these units when
electric heat package is installed.
NOTES:
1. In compliance with NEC requirements for multimotor and combina-
tion load and equipment (refer to NEC Articles 430 and 440), the
overcurrent protective device for the unit shall be fuse or HACR
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 per-
cent of voltage imbalance.
% Voltage Imbalance
Example: Supply voltage is 460-3-60.
AB = 452 v
BC = 464 v
AC = 455 v
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
maximum allowable 2%.
IMPORTANT: If the supply voltage phase imbalance is more than
2%, contact your local electric utility company immediately.
3. Non-fused disconnect switch cannot be used when rooftop unit
electrical ratings exceed 80 amps.
FLA — Full Load Amps
HACR — Heating, Air Conditioning
and Refrigeration
IFM — Indoor Fan Motor
LRA — Locked Rotor Amps
MCA — Minimum Circuit Amps
MOCP — Maximum Overcurrent
Protection
NEC — National Electrical Code
OFM — Outdoor-Fan Motor
RLA — Rated Load Amps
= 100 x
max voltage deviation from average voltage
average voltage
Average Voltage =
452 + 464 + 455
3
=
1371
3
= 457
7
457