Method 2:
External
of chiller
contactor
CX CX CX
COMP OF PUMP
aux aux aux
PCB
EXTERNAL
SWITCHBOARD
C/W STARTERS
R
R
R
This method is the same as the previous one, with the exception that the staters will supply
the power directly to the compressor, fan motor and pump. The contactors in the chiller unit
only act to provide an auxillary signal to activate the starters in the external board.
Because of this, the overload protection of the compressor (CO) and pump (PO) will no
longer function in the PCB. Rather, the overload protection is now dependent on the overload
settings in the external board.
All the other safety protection devices will still be in operation.
Method 3:
For the third method, the entire control box is not used at all. Rather the entire power
switching and protection is taken up by the external board.
Power cables from the external board will be connected to the terminal blocks of the control
box. All contactors and PCB is bypassed.
This method is not recommended because of the importance of proper protection of the
water side, i.e. anti-freeze and water temperature setting. Transferring the wiring to the
external board may result in incorrect or insufficient protection.
Section 11 Page 139
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