Screw Compressor Central Chiller
Chapter 2: Functional Description
14
Fail Safe Operation
If a safety device or circuit should fail, the design must be such that the failure causes a
“Safe” condition. As an example, a safety switch must be a normally open switch. The switch
must be held closed with the device it is to protect. If the switch fails, it will go to the open
condition, tripping out the safety circuit.
At no time should the safety device fail and allow the operation to continue.
For
example, if a safety switch is guarding a motor, and the safety switch fails, the motor should
not be able to run.
Safety Device Lock-Outs
Some safety devices disconnect electrical energy from a circuit. The safety devices that are
used on these chillers are primarily concerned with electrical power disconnection and the
disabling of moving parts that may need to be accessed during the normal operation of the
machine.
Some of the safety devices utilize a manual activator. This is the method of initiating the
safety lock out. This may be in the form of a plug, lever or a handle. Within this lockable
handle, there may be a location for a padlock. Personnel servicing the equipment should
place a padlock in the lockout handle.
In addition to the safety devices listed above, these chillers are equipped with a line cord
plug. This allows the operator or maintenance personnel to unplug the chiller from its power
source and tag it out. The plug can then be tagged with any number of approved electrical
lockout tags available at most electrical supply stores.
WARNING!
Always disconnect and lockout all electrical power and pneumatic (i.e. compressed air)
sources prior to servicing or cleaning the chiller. Failure to do so may result in serious
injury. No one but the person who installed the lockout may remove it.
