Philips V24CT User's Reference Manual page 323

Installation Information
Safety Ground
Additional Protective Earth (Secondary Ground Wire) Hazardous
(Protective leakage currents can be caused when other equipment is
Earth)
interconnected with either monitor.
(V24 and V26
A secondary ground wire is provided with the CMS, V24 and V26 to
only)
comply with IEC 601-1-1. This additional protection ensures against
excessive chassis leakage current in the event of a single fault in the
health care facility's primary grounding means.
It is recommended that the secondary ground wire be connected to a
ground source separate from the primary grounding source found in the
instruments' power source.
This cord should be permanently attached to either monitor mainframe
rear panel attachment screw.
Check each time before use that the monitor is in perfect working order.
The cable connecting the patient to the instrument must be free of
electrolyte.
Monitor Installation and Patient Safety 11-7