NF50 AND NF100 CIRCUIT BREAKER QUICK START MANUAL
5
n
PRECAUTIONS
•
Withstand Voltage Test A guide for the test is given on the
following. Do not perform a withstand voltage test exceeding these
levels. (Note) Test the operating circuit between the live section and
ground.
(Application time: one minute) (Unit: V)
Main Circuit
Auxiliary Circuit or Control Circuit
Rated insulation
voltage
Test voltage
(effective value for
alternating current)
Rated insulation
voltage of operating
circuit
Test voltage
(effective value for
alternating current)
U
i ≤300
2000
U
is ≤60
1000
300<
U
i ≤690
2500
60 <
U
is≤690
2
U
is +1000
(min. 1500)
•
Insulation Resistance Measurement and Withstand Voltage Test
The restrictions a and b apply to the following models. Applicable
models: Earth leakage circuit breaker, Measuring display unit
breaker.
Measurement Position
Test
Insulation
Resistance
Measurement
Withstand
Voltage Test
State of Handle
ON
OFF
ON
OFF
Between Live Section of Main Circuit
and Ground
O
O
O
O
Bet
w
een Dif
fer
ent P
oles
Line Side
Between left - middle, middle
- right, left - right poles
u
O
X
O
Between left - neutral pole,
middle - neutral poles right -
neutral poles
O (
u
) (*1) O
O (X) (*1) O
Load Side
Between left - middle, middle
- right, left - right poles
u
u
X
X
Between left - neutral poles,
middle - neutral poles right -
neutral poles
O (
u
) (*1) O (
u
) (*1) O (X) (*1) O (X) (*1)
Between Power - Load Side
Terminals
-
O
-
O
Between Main Circuit Live Sections -
Operating Circuit Live Sections
O
O
O
O
Between Operating Circuit Live
Section - Ground
O
O
O
O
Note *1 Values in parentheses apply for measuring display unit breaker.
PERIODIC INSPECTIONS
To prevent trouble and ensure the breaker operates safely for a long
time, inspect the breaker one month after starting use and periodically
thereafter according to the environmental conditions.
Inspection Interval Guide
1
Clean and dry environment
Once every 2 to 3 years
2
Environment with low levels of dust,
corrosive gas, vapors, salt, etc.
Once a year
3
Places other than 1 or 2
Once every six months
Model
Inspection
items
Criterion
Remarks
Common
Are any of the
conductors
loose?
No conductor must be loose.
Is any cover
or base
cracked? Is
any handle
damaged?
There must be no cracks, damage
or breaks.
If any conductor is
loose, tighten again
with the appropriate
torque.
Has the
breaker been
submerged
and infiltrated
with water?
Is the breaker
heavily dirtied
by mud or
dust?
There must be no infiltration of
water, heavy mud or dust.
Has the
temperature
risen
abnormally?
(1) Visually inspect that none
of the studs on the backs of
the terminals, or the breaker’s
tightened or molded sections are
discolored from burning.
(2) There must be no specially
high temperature rise when the
current at each phase is balanced.
(Tolerable maximum value for
terminal temperature rise: 60K)
(3) There should be no difference
on the left and right side of the
base sides if the load current is
balanced.
If water has
infiltrated the
breaker, it must be
replaced with a new
part or overhauled
by the Mitsubishi
Service Center.
Amzsupport@
meau.com
Can the
handle be
turned ON
and OFF
smoothly?
Should operate smoothly.
There may be a
light temperature
difference between
the following
terminals.
Between the power
side terminal and
load side terminal
Between the center
pole terminal and
left and right pole
terminals.
Does
pressing the
TRIP button
result in a
trip?
Must be resettable after tripping.
Open and close
a normally closed
breaker periodically.
This will clean the
contact and prevent
abnormal heating.
Inspection after Tripping. Whether the circuit breaker can be reused
or must be replaced after switching off a fault current depends on the
intensity of the current which was switched off.
Intensity of trip current, degree of MCCB damage, and
countermeasures
Intensity of Trip Current
Degree of MCCB
Damage
Countermeasures
When it is clear that the
circuit breaker operated
within the time-delay trip
range (Overcurrent up to
10 times of rated current)
No abnormality such as
contamination around vent
observed
Reusable. (The circuit
breaker can function 50
times (100A or less) at
overload current which is
6 times higher than rated
current)
Relatively low short-circuit
current which causes
instantaneous tripping
i
Large short-circuit current
close to rated breaking
capacity
Soot and dust found near
vent.
i
Soot and dust found
near handle, remarkable
contamination found near
vent. Molten metal found
in circuit breaker. Box of
box type circuit breaker is
severely deformed
Reusable
i
Replace with a new part
Mitsubishi Electric Automation, Inc.
