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.
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