IBM 6400 series Maintenance Manual page 354

Customer Power Source Service Check
Use an ECOS Electrical Safety Tester (P/N 6339695) in the United States or
a similar safety tester in other countries.
NOTE: The ECOS tester will trip ground fault detector protected outlets.
Plug the ECOS meter into the customer's outlet. Follow the instructions
supplied with the meter to test for the following:
1. Wiring errors
2. Low voltage
3. Neutral to ground short
4. Ground path impedance
5. Neutral impedance
NOTE: The customer is responsible for correcting problems with the power
Each branch circuit must be grounded for safety and correct operation of the
printer. This ground must be connected either to the electrical service ground
or to a suitable building ground. The printer power cable has a green or
green/yellow insulated grounding conductor. This is not a neutral.
Power Cable
1. Make sure the power cable is not damaged.
2. Make sure the power plug is the correct type.
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This is a good test of the ground fault detector. Reset the outlet as
needed.
source. Inform the IBM Installation Planning Representative (IPR) of
any problems with the customer's power source.
Safety Inspection Guide