Protection Limits
The Keysight 34450A 5½ Digital Multimeter
provides protection circuitry to prevent
damage to the instrument and to protect
against the danger of electric shock, pro-
vided that the Protection Limits are not
exceeded. To ensure safe operation of the
instrument, do not exceed the Protection
Limits shown on the front panel, as defined
below:
Note: The front-panel terminals and current
protection fuse are shown above.
Input Terminal Protection
Limits
Protection Limits are defined for the input
terminals:
Main Input (HI and LO) Terminals. The HI
and LO input terminals are used for voltage,
resistance, capacitance, and diode test
measurements. Two Protection Limits are
defined for these terminals:
HI to LO Protection Limit. The Protection
Limit from HI to LO ("A" in the figure
above) is 1000 VDC or 750 VAC, which is
also the maximum voltage measurement.
This limit can also be expressed as
1000 Vpk maximum.
LO to Ground Protection Limit. The LO
input terminal can safely "float" a maxi-
mum of 500 Vpk relative to ground. This is
Protection Limit "B" in the figure.
Although not shown on the figure, the Pro-
tection Limit for the HI terminal is a maxi-
mum of 1000 Vpk relative to the ground.
Therefore, the sum of the “float” voltage
and the measured voltage must not exceed
1000 Vpk
Current Input Terminal. The current input
("I") terminal has a Protection Limit of
100 mA (rms) maximum current flowing
from the LO input terminal. This is Protec-
tion Limit "C" in the figure. Note that the
current input terminal will be at approxi-
mately the same voltage as the LO terminal.
Note: The current-protection circuitry
includes a fuse on the back panel. To main-
tain protection, replace this fuse only with a
fuse of the specified type and rating.
10 A Current Input Terminal. The 10 A cur-
rent input terminal has a Protection Limit of
10 A (rms) maximum current flowing from
the LO input terminal. This is Protection
Limit "D" in the figure. Note that the current
input terminal will be at approximately the
same voltage as the LO terminal.
Note: The current-protection circuitry
includes an internal fuse. To maintain pro-
tection, service-trained personnel should
replace this fuse only with a fuse of the
specified type and rating.
Sense Terminal Protection
Limits
The HI and LO sense terminals are used
only for four-wire resistance measurements
("
Ω 4W"). The Protection Limit is 200 Vpk
for all of the terminal pairings ("E" in the fig-
ure):
LO sense to LO input.
HI sense to LO input.
HI sense to LO sense.
Note: The 200 Vpk limit on the sense termi-
nals is the Protection Limit. Operational
voltages in resistance measurements are-
much lower - less than 5 V in normal opera-
tion.
IEC Measurement Category II
Overvoltage Protection
To protect against the danger of electric
shock, the Keysight 34450A 5½ Digital Mul-
timeter provides overvoltage protection for
line-voltage mains connections meeting
both of the following conditions:
The HI and LO input terminals are con-
nected to the mains under Measurement
Category II conditions, defined below, and
The mains are limited to a maximum line
voltage of 300 VAC.
IEC Measurement Category II includes elec-
trical devices connected to mains at an out-
let on a branch circuit. Such devices include
most small appliances, test equipment, and
other devices that plug into a branch outlet
or socket. The 34450A may be used to make
measurements with the HI and LO inputs
connected to mains in such devices, or to
the branch outlet itself (up to 300 VAC).
However, the 34450A may not be used with
its HI and LO inputs connected to mains in
permanently installed electrical devices
such as the main circuit-breaker panel,
sub-panel disconnect boxes, or permanently
wired motors. Such devices and circuits are
subject to overvoltages that may exceed the
protection limits of the 34450A.
Note: Voltages above 300 VAC may be mea-
sured only in circuits that are isolated from
mains. However, transient overvoltages are
also present on circuits that are isolated
from mains. The 34450A is designed to
safely withstand occasional transient over-
voltages up to 2500 Vpk. Do not use this
multimeter to measure circuits where tran-
sient overvoltages could exceed this level.
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