HP 400D Operating And Servicing Manual page 8

Both the black binding posts and the instrument case will be connected to the power system
ground when the instrument is used with the standard
by connecting only ground potential circuits to the black binding posts.
Ground loops may affect the accuracy of low voltage measurements.
the accuracy by inserting an ungrounded adapter in the instrument power circuit.
CA
UT I ON
INSERT UNGROUNDED
ADAPTER TO BREAK
GROUND LOOP
,
'- - - - POSSIBLE
-
CA
UT I O N
ONE SIDE OF POWER
LINE IS ALSO
GROUNDED
NEMA
A void short circuits
receptacle.
GROUND LOOP - -
-
Open the loop and restore
REPRO
,
--'
-
�
REPRO