Electrical Data; Electrical Service Sizing - Trane IntelliPak RA 20 Installation, Operation And Maintenance Manual

Electrical Data

Electrical Service Sizing

To correctly size electrical service wiring for a unit, find
the appropriate calculations listed below. Each type of
unit has its own set of calculations for MCA (Minimum
Circuit Ampacity) and MOP (Maximum Overcurrent
Protection). Read the load definitions that follow and
then find the appropriate set of calculations based on
unit type.
N N o o t t e e : : Set 1 is for cooling only and cooling with gas
heat units, and set 2 is for cooling with electric
heat units.
Load Definitions: (To determine load values, see the
Electrical Service Sizing Data Tables on the following
page.)
Load Definitions
Current of the largest motor (compressor or fan
LOAD 1
motor)
Sum of the currents of all remaining motors
LOAD 2
LOAD 3 Current of electric heaters
Any other load rated at 1 amp or more
LOAD 4
Set 1: Cooling Only Rooftop Units and
Cooling with Gas Heat Rooftop Units
MCA = (1.25 x LOAD1) + LOAD2 + LOAD4
MOP = (2.25 x LOAD1) + LOAD2 + LOAD4
Select a fuse rating equal to the MOP value. If the MOP
value does not equal a standard fuse size as listed in
NEC 240-6, select the next lower standard fuse rating.
N N o o t t e e : : If selected MOP is less than the MCA, then select
the lowest standard maximum fuse size which is
equal to or larger than the MCA, provided the
selected fuse size does not exceed 800 amps.
Set 2: Rooftop units with Electric Heat
S S i i n n g g l l e e S S o o u u r r c c e e P P o o w w e e r r u u n n i i t t s s ( ( 4 4 6 6 0 0 V V a a n n d d 5 5 7 7 5 5 V V ) )
To arrive at the correct MCA and MOP values for these
units, two sets of calculations must be performed. First
calculate the MCA and MOP values as if the unit was in
cooling mode (use the equations given in Set 1). Then
calculate the MCA and MOP values as if the unit were
in heating mode as follows. (Keep in mind when
determining LOADS that the compressors and
condenser fan motors don't run while the unit is in
heating mode).
For units using heaters less than 50 kW:
RT-SVX063E-EN
MCA = 1.25 x (LOAD1 + LOAD2 + LOAD4) + (1.25 x
LOAD3)
For units using heaters equal to or greater than 50 kW:
MCA = 1.25 x (LOAD1 + LOAD2 + LOAD4) + (1.0 x
LOAD3)
The nameplate MCA value will be the larger of the
cooling mode MCA value or the heating mode MCA
value calculated above.
MOP = (2.25 x LOAD1) + LOAD2 + LOAD3 + LOAD4
The selection MOP value will be the larger of the
cooling mode MOP value or the heating mode MOP
value calculated above.
Select a fuse rating equal to the MOP value. If the MOP
value does not equal a standard fuse size as listed in
NEC 240-6, select the next lower standard fuse rating. If
the selected MOP value is less than 125 percent of the
current rating of the electric heat load, select the next
higher standard fuse rating.
N N o o t t e e : : If selected MOP is less than the MCA, then select
the lowest standard maximum fuse size which is
equal to or larger than the MCA, provided the
selected fuse size does not exceed 800 amps.
D D u u a a l l S S o o u u r r c c e e P P o o w w e e r r u u n n i i t t s s ( ( 2 2 0 0 0 0 V V a a n n d d 2 2 3 3 0 0 V V ) )
These units will have two circuit values shown on the
nameplate. The first circuit value will be the
refrigeration (cooling mode) values calculated per Set
1. The second set of circuit values shown on the
nameplate will be for the electric heating circuit as
follows.
For units using heaters less than 50 kW:
MCA = (1.25 x LOAD3)
For units using heaters equal to or greater than 50 kW:
MCA = (1.0 x LOAD3)
MOP = (1.25 x LOAD3)
Select a fuse rating for the electric heating circuit that is
equal to the MOP value obtained in the equation above.
If the MOP value does not equal a standard fuse size as
listed in NEC 240-6, select the next lower standard fuse
rating (see note below for exception). If the selected
MOP value is less than 125 percent of the current rating
of the electric heat load, select the next higher standard
fuse rating.
N N o o t t e e : : If the available MOP option is less than the MCA
obtained in the equation above, then reselect the
lowest standard maximum fuse size which is
equal to, or larger, than the MCA, provided the
reselected fuse size does not exceed 800 amps.
I I n n s s t t a a l l l l a a t t i i o o n n
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