Safety Grounding Considerations - Newport New Focus Picomotor 8743-CL User Manual

22 Introduction
1.4

Safety Grounding Considerations

There are potentially lethal voltages generated within the Model 8743-CL Picomotor
Controller/Driver and presented on the pins of the "Motor" connectors EVEN
WHEN NO PICOMOTOR IS INSTALLED. (These voltages are not present when
power is not applied to the unit. They are not present when the unit is switched
OFF.) The User must manage certain system-level aspects to ensure safe operation.
One of these is grounding.
The Model 8743-CL's external DC power supply provides 12VDC. The negative
output from this supply is typically isolated from MAINS earth ground, but this
isolation should not be assumed. This same negative output is connected directly to
the Model 8743-CL's external case within the Model 8743-CL. This same "ground"
is at the same potential as the MOTOR connectors' return signal pins. This means
that the MOTOR connectors' drive signal pins are, at times, at VERY HIGH
VOLTAGES relative to the Model 8743-CL case, the USB connector shell, and the
DC input/loop-through connectors' negative terminals.
An 8-32 screw is provided on the unit and marked with the "Ground" symbol shown
in Paragraph 1.1.8, above. While it is not necessary to connect this terminal to a
building "earth" ground, New Focus recommends doing so because it will simplify
system-level compliance with most regulatory requirements. Once this connection
is made, the user must ensure that all other system components are appropriately
grounded. Do not depend upon the physical mounting hardware to accomplish this
grounding.
If the other components are not grounded, a damaged Picomotor (or its wire) could
result in a dangerously high voltage being present between anything that is grounded
(like the 8743-CL and a computer attached to it via USB) and the Picomotor case.
Note that the simplest way to ground a Picomotor is via its threaded mounting
bushing or other mounting hardware. DO NOT ATTEMPT TO OPEN A
PICOMOTOR TO ACHIEVE THIS GROUNDING.
If system requirements prevent the Picomotor from being grounded, then the user
must ensure that the Model 8743-CL and all other system components (including
any USB-connected computers) are properly isolated from earth ground. This is
because a short of the high-voltage drive signal to an earth ground may result in
potentially lethal voltages existing between the case of the 8743-CL and anything
that is earth grounded, such as a floor. The User is advised to consult all applicable
regulations because this insulation will probably need to have a breakdown voltage
of several thousand volts due to lightening concerns.
In summary, New Focus strongly recommends grounding the Model 8743-CL's
case.