71
8.1.2 Low Temperature Application
In conditions where temperatures reach as low as
–5˚C special MCCBs are usually required. Mitsubishi,
however, have tested their standard MCCBs to tem-
peratures as low as –10
°
C without any detrimental
effects.
For conditions where temperatures drop below
–10˚C special MCCBs must be used.
If standard MCCBs experience a sudden change
from high temperature, high humidity conditions to low
temperature conditions, there is a possibility of ice
forming inside the mechanism. In such conditions we
recommend that some form of heating be made avail-
able to prevent mal-operation.
In conditions of low temperature MCCBs should
be stored in either the tripped or OFF position.
Low Temperature MCCBs
Special low temperature MCCBs are available that
can withstand conditions where temperatures fall to
as low as –40˚C. These special MCCBs are available
in sizes up to 1200A in the standard series and above
50A in the compact series.
8.1.3 High Humidity
In conditions of high humidity the insulation resistance
to earth will be reduced as will the electrical life.
For applications where the relative humidity ex-
ceeds 85% the MCCB must be specially prepared or
special enclosures used. Special preparation includes
plating all metal parts to avoid corrosion and special
painting of insulating parts to avoid the build up of
mildew.
There are two degrees of tropicalisation:
Treatment 1- painting of insulating material to avoid
build up of mildew plus special plating
of metal parts to avoid corrosion.
Treatment 2- painting of insulating material to avoid
build up of mildew only.
8.1.4 Corrosive Atmospheres
In the environment containing much corrosive gas, it
is advisable to use MCCB of added corrosion resis-
tive specifications.
For the breakers of added corrosionproof type,
corrosion-proof plating is applied to the metal parts.
Where concentration of corrosive gas exceeds the
level stated below, it is necessary to use MCCB of
added corrosion resistive type being enclosed in a
water-proof type enclosure or in any enclosure of pro-
tective structure.
Allowable containment for corrosive gas.
H
2
S
0.01ppm SO
2
0.05ppm
NH
3
0.25ppm
8.1.5 Affecting of Altitude
When MCCBs are used at altitudes exceeding 2000m
above sea level, the effects of a drop in pressure and
drop in temperature will affect the operating perfor-
mance of the MCCBs. At an altitude of 2200m, the air
pressure will drop to 80% and it drops to 50% at
5500m, however interrupting capacity is unaffected.
The derating factors that are applicable for high alti-
tude applications are shown in table 8.3. (According
to ANS
I
C 37.29-1970)
Table 8.3 Derating Factors for High Altitude Appli-
cations
Altitude
3000m
4000m
5000m
6000m
Rated current
0.98
0.96
0.94
0.92
Rated voltage
0.91
0.82
0.73
0.65
For example: NF800-SEP on 4000m
1. Voltage
The rated operating voltage is AC690V. You should
derate by 690x0.82=565.8V. It means that you can
use this NF800-SEP up to AC565.8V rated voltage.
2. Current
The rated current is 800A. You should derate by
800x0.96=768A. It means that you can use this
NF800-SEP up to 768A rated current.
8.2 Vibration-Withstand Characteristics
8.2.1 The Condition of Test
1. Installation position and Direction of vibration
• Every vertical and horizontal at vertical installed
(as shown in Fig. 8.1)
2. The position of MCCBs and vibration time
Forty minutes in each position (ON, OFF and TRIP)
3. Vibration criteria
• Frequency
10~100Hz
• Vibration acceleration
22 m/s
2
• Period
10min./cycle
8.2.2 The Result of Test
The samples must show no damage and no change
of operating characteristic (200% release), and must
not be tripped or switched off by the vibration.
Vertical
Wire
connection
Horizontal
Fig. 8.1 Applied Vibration
