Grounding Of Station Protectors; Station Protectors Functional Check; Ground Potential Difference (Gpd) - IBM 5500 Operational, Installation, And Maintenance Manual

Grounding of Station Protectors

Station Protectors Functional Check

Ground Potential Difference (GPD)

104
Chapter 6: Twinax Client Cabling Requirements and Problem Solving
building and as close as possible to a suitable ground as described in
"Grounding of Station Protectors" on page 104. It is the responsibility of the
customer to supply, install, and maintain station protectors, and to obtain
spare units if they are required.
For detailed station protector installation information refer to the IBM 5250
Information Display System: Planning and Site Preparation Guide (GA21-
9337).
The minimum grounding requirements are a wire of at least #6 AWG
(equivalent to an outside diameter of 4.7 mm, or a cross sectional area of
17.36 square mm), less than 3 meters (10 feet) long, running in a straight line
to a grounding electrode with less than 10 ohms resistance to ground. The
twinax cable attaching to the station protector next to the grounding conductor
must be the one leading to the outside of the building.
Although station protectors are totally the customers responsibility, the
following checks can be made to ensure the devices are in good working
order.
Disconnect both twinax cables from the protector, and remove the cover. The
protector contains 24 diodes. The resistance of each diode should be more
than 10,000 ohms (negative meter lead to anode) and less than 2,000 ohms
(negative meter lead to cathode). The protector contains 2 capacitors. Set your
voltmeter to the 100,000 ohm resistance scale. Touch the meter leads across
the leads of a capacitor. You should notice an instantaneous meter deflection
as the capacitor charges up. No deflection indicates a defective capacitor. An
analog meter should be used for this test.
A ground potential difference is when two or more ground points have a
different electrical potential. This can cause problems for a twinax
installation, as the twinax shield is connecting these points together. This can
cause a large current to flow in the twinax shield, as it attempts to equalize the
two grounds.
Causes for GPD
Differences in ground potential generally occur when the installation has
twinax cables running between different buildings, uses different power
distribution substations in the same building, or has defective grounding.
The following common tests will help you to resolve these problems:
Resolving GPD Problems
The IBM 5250 Information Display System: Planning and Site Preparation
Guide (GA21-9337) specifies the recommended cable wiring between
Planning, Installation, and Maintenance Guide