Ac Power Network And Ground - Texas Instruments 880 User Manual

POWER
COMPANY
TRANSFORMER
POWER
COMPANY
EARTH
GROUND
seRVICE
ENTRANCE
EARTH
GROUND
ROD
CIRCUIT
BREAKER
PANEL
DATA TERMINAL
OR
COMPUTER EQUIPMENT
RECEPTACLE
Figure 0-1. AC Power Network and Ground
NOTE1: Neutral and protection ground are connected together at a single point where power comes into the site (service entrance).
NOTE 2: Neutral and protection ground are isolated from each other except where connected at the service entrance.
NOTE 3: Neutral and protection ground are isolated from the conduit except where connected at the service entrance. This is done
with a HUBBELL IG-5262 receptacle connected to comply with the National Electrical Manufacturers Association Specifica-
tion, NEMA 5-15R.
NOTE 4: The protection ground wire must have a resistance of less than 1 ohm.
NOTE 5: Earth ground must have a resistance of less than 1 ohm.
0.4 SINGLE-POINT GROUNDING RULE
Protection ground is connected to the printer
frame (chassis ground), which is connected to
earth ground through the ac power cable. Signal
ground is the common reference voltage level for
all the interface circuits except protection ground.
Signal ground and protection ground are con-
nected; this connection must be made at only one
point in a directly connected system to prevent a
ground loop. A ground loop results in current that
can cause faulty operation of the equipment.
Incorrect characters, parity errors, characters not
printed, and even component damage can be
symptoms of multiple system grounds. If these
problems appear, the signal-ground/protective-
D-2
ground connection must be checked, and the cor-
rect configuration made.
Normally, the connection between protection
ground and signal ground is made in the equip-
ment with the greatest ac power (current) require-
ment. When the printer is connected directly to a
system, such as a host computer that uses more
ac current than the printer, it is recommended that
the single point ground be made at that system
and not at the printer. The data cable must have a
protection ground wire. When the cable does not
have a protection ground, connections must be
made to short the protection ground and signal
ground in the printer and in the modem or host
computer on the other end of the data cable. This
connection must be as specified by the equipment
company and not made in the data cable.