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Requirements
The second situation concerns auxiliary relays. There is a limitation to the numbers of
continuously energized auxiliary relays that may be included in a RHGS or RHGX case
or equipment frame and still stay within the 15°C rise limit. For example in an applica-
tion of FRQWLQXRXVO\ HQHUJL]HG interposing relays. It is the temperature rise rather than
the physical space which may limit the number of relays in a case or frame.
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Concerning permissible relay power losses in cases of type RHGS or RHGX, consider-
ation must be given to how the case is mounted when defining the permissible power
losses.
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1. Take the calculated temperature increase within the case
2. Add the temperature increase of the air in the cubicle
3. Calculate the total temperature increase in the case in relation to room temperature
5HOD\LQJ HTXLSPHQW LQ FXELFOH
Table 60
states the recommended values of permissible power losses of relaying equip-
ment mounted in the D-plane (hinged frame or front plane) and the B-plane (rear
mounting plane).
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%SODQ ,W LV QRW UHFRPPHQGHG WR PRXQW UHOD\V LQ WKH %SODQH DV WKH DLU FLUFXODWLRQ LV
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A calculation of the temperature rise within an RHGS or RHGX case mounted in a cu-
bicle is shown in
equation
Θ
K
P
K
P
=
+
+
+
relay
H
H
S
Where:
Θ
is the increase of the ambient temperature of the relay
relay
K
is the RHGS or RGHX case thermal resistance
H
1.
S
&KDSWHU
0RXQWLQJ LQ FXELFOHV
(Equation 1)
105
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