Mitsubishi Electric MS-T Series - Recommended Product Update Interval; Maintenance and Inspection Check List

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(4) Ambient temperature and settling current
The TH-T series thermal overload relay is adjusted based on an ambient temperature of 20°C when used
in the standard boxed magnetic motor starter (MS type). (The temperature in the control panel for the
MSO type magnetic motor starter is 35°C.) The TH-T type thermal overload relay is equipped with an
ambient temperature compensation device, so the operating characteristics are less likely to be affected
by the ambient temperature changes. Figures 1 and 2 show the minimum operating currents at different
temperatures with the reference ambient temperature of 20°C (in-control panel temperature of 35°C).
Thermal overload relay characteristic is affected by the ambient temperature; when the ambient
temperature is low, the operating current is large, and when the temperature is high, the operating
current is small. If the ambient temperature of where the magnetic motor starter is mounted greatly
differs from 20°C (in-control panel temperature of 35°C), the settling current of the thermal overload
relay must be compensated according to Figures 1 and 2. The size of the compensation rate is
determined by the adjusting dial’s position (minimum scale > center scale > maximum scale), so
caution is required when compensating. (Note that if the tolerable working temperature of 40°C (55°C)
is exceeded, the unit could function at a current less than 100% of the settling current.)
110
-10
（5）
0
（15）
10
（25）
30
（45）
40
（55）
周囲温度 （℃）＊1
（制御盤内温度（℃ ））＊2
108
106
104
102
98
96
94
92
90
20
（35）
補
正
率
（
％
）
TH-T25（KP）
最大目盛
中央目盛
最小目盛
110
-10
（5）
0
（15）
10
（25）
30
（45）
40
（55）
108
106
104
102
98
96
94
92
90
20
（35）
周囲温度 （℃ ）＊1
（制御盤内温度（℃ ））＊2
補
正
率
（
％
）
TH-T18（KP）
最大目盛
中央目盛
最小目盛
Fig. 1 Ambient temperature compensation curve Fig. 2 Ambient temperature compensation curve
(T18 frame) (T25 frame)
Compensation rate: Percent in respect to the minimum operating current at the ambient temperature
of 20C (in-control panel temperature of 35°C)
<Settling current compensation method>
In the curves in Figures 1 and 2, find the compensation rate at the working ambient temperature.
Divide the motor’s full load current by the identified compensation rate. The obtained value is the
settling value.
(Example: When the TH-T25's ambient temperature is 40°C (55°C inside control panel), the
compensate rate at the temperature with the minimum scale is 97% according to Figure 2. If the
motor’s rated current is 15A, the settling value is obtained as 15.5A (=15÷0.97).)
Note 1: [*1] Applicable ambient temperature for MS type indicates temperature outside the box.
[*2] Indicates temperature including temperature rise in control panel applicable for MSO type.
(5) Connection wire size
The heat generated from the thermal overload relay differs according to the connected wire size, and
thus affects the characteristics. The minimum operating current for the TH type has been adjusted with
the reference connected wire sizes shown in Table 2, so if a wire thinner than this size is connected,
the generated heat will be higher, and the minimum operating current will be smaller. On the other
hand, if a thicker wire is used, the minimum operating current will increase.
Thus, when using a wire of a size differing from the reference connection wire size, strictly speaking, the
settling current must be compensated. For example, for the TH-T25 type used with the heater nominal
and settling current of 15A and with a 6mm
2
wire, the operating current fluctuation rate is 104% according
to Table 2. Using the rate, compensate the scale to the 151/1.04  14.4 (A).
Table 2 TH type thermal overload relay connection wire size and ultimate operating current
Type
Heater
designation
(A)
Reference
connection wire size
(mm
2
)
Connection
wire size
(mm
2
)
Minimum operating
current fluctuation rate
(％)
TH-T18 (KP) 0.12 to 15
TH-T25 (KP) 0.24 to 11
2
1.25
2.5
98
103
TH-T25 (KP) 15, 22 3.5
2
6
97
104
.
.
Maximum scale
Center scale
Minimum scale
Compensation
rate
A
mbient temperature (°C)*1
(Temperature in control
panel °C
)
*2
Compensation
rate
A
mbient temperature (°C)*1
(Temperature in control
panel °C
)
*2
Maximum scale
Center scale
Minimum scale