70
8. ENVIRONMENTAL CHARACTERISTICS
High temperature
Low temperature
High humidity
High altitude
Dirt and dust
Corrosive gas, salt air
Environment
Trouble
Countermeasures
1. Nuisance tripping
2. Insulation deterioration
1. Condensation and freezing
2. Low-temperature fragility in shipping
(around –40˚C)
1. Insulation resistance loss
2. Corrosion
1. Reduced temperature, otherwise no
problem up to 2,000m
1. Contact discontinuity
2. Impaired mechanism movement
3. Insulation resistance loss
1. Corrosion
1. Reduce load current (derate).
2. Avoid ambients above 60˚C.
1. Install heater for defrosting and drying.
2. Ship tripped, or if not possible, OFF.
1. Use MCCB enclosure such as Type W.
2. Inspect frequently, or install high-
corrosion-resistant MCCBs.
1. See “Low temperature”, above.
1. Use Type
I
MCCB enclosure.
1. Use Type W MCCB enclosure or install
high-corrosion-resistant MCCBs.
5
:
Table 8.1 Abnormal Environments, and Countermeasures
8.1 Atmospheric Environment
Abnormal environments may adversely affect perfor-
mance, service life, insulation and other aspects of
MCCB quality. Where service conditions differ sub-
stantially from the specified range as below, derating
of performance levels may result.
1. Ambient temperature range
–10˚C~+40˚C (Average
temperature for 24 hours,
however, shall not be
higher than 35˚C.)
2. Relative humidity
85% max. with no dewing
3. Altitude
2,000m max.
4. Ambient
No excessive water or oil
vapour, smoke, dust, salt
content, corrosive sub-
stance, vibration, and im-
pact
Expected service life
(MTTF) under the above
conditions is 15 years.
8.1.1 High Temperature Application
To comply with relevant standards, all circuit break-
ers are calibrated at 40˚C. If the circuit breaker is to
be used in an environment where the ambient tem-
perature is likely to exceed 40˚C please apply the de-
rating factor shown in table 8.2.
For example: To select a circuit breaker for use on a
system where the full load current is 70A in an ambi-
ent temperature at 50˚C then from table 8.2
0.9
70A
= 77.8A
Select a circuit breaker with a trip unit adjustable from
80-100A or fixed at 100A.
Table 8.2 MCCB Derating
Ambient Temperature (°C)
50
55
60
Derating factor
0.9
0.8
0.7
