Operation
ASCO Model K875A Outdoor Load Bank
4-6
Secondary Current Calculation
The controller senses the current (Isense), delivered from the current transformer that is monitoring
the building load. This value can be determined using the following formula:
I(sense) = I(line)/ CT Ratio.
In this example, the CT Ratio = 3000/5 or 600.
For TP.1 I(sense) = 721/600 or 1.20 amps.
(600 kW)
For TP.2 I(sense) = 1322/600 or 2.20 amps.
(1100 kW)
For TP.3 I(sense) = 1563/600 or 2.60 amps.
(1300 kW)
For TP.4 I(sense) = 1683/600 or 2.80 amps.
(1400 kW)
For TP.5 I(sense) = 1803/600 or 3.01 amps.
(1500 kW)
For TP.6 I(sense) = 1863/600 or 3.11 amps.
(1550 kW)
Adjustments can be made to the PC board controller(s) via the adjustable resistor potentiometers
found on the PC board(s). (Reference resistors labeled R73, R60, R47, R34, and R21.)
NOTE
If more than five load steps are required, there will be one additional
PC board (A102). The resistor potentiometers are labeled identically
to the first PC board (A101).
NOTE
R73 controls the last load step circuit. [i.e., if the Load Bank has five
load steps, R73 controls the fifth load step; if the Load Bank has six
load steps, R21 (on the second PC board) controls the sixth load
step.]
The potentiometers should be adjusted such that the last load step is the first step to be “shed”.
PCB A101
PCB A102
In this example,
R73 = TP.2
R21 = TP.1
R60 = TP.3
R47 = TP.4
R34 = TP.5
R21 = TP.6
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