Siemens AS 235 appendix Permissible thermal loading, Standard cabinet with heat exchanger

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Automation systems

Standard cabinets

Permissible thermal loading

Permissible thermal loading, configuring guidelines ￿Standard cabinets without forced ventilation

Basic and extension units fitted in standard cabinets can be operated without fans if

• the cabinet thermal load Ps max permissible depending on the cabinet unit temperature is not exceeded and

• a heat loss greater than 150 W does not occur in any extension system.

If many I/O modules are used with a high heat loss, these should not all be fitted next to one another but distributed amongst the various subracks in order to prevent heat accumulation. Ps max is usually not achieved in the extension cabinet even with the full configuration of 42 I/O modules. An exact determination of the total heat loss is only required with a non-typical module config- uration (many I/O modules of the same type, modules with more than 8 W heat loss).

Standard cabinets with degree of protection IP 20, with forced ventilation

Extension unit with > 150 W/subrack

Basic and extension cabinets whose thermal load (without fan subassembly) is not exceeded must be provided with forced ventilation if an extension unit is configured with I/O modules such that the heat loss of this subrack exceeds 150 W. At least one fan subassembly must then be provided between the basic unit GE and the 1st extension unit EE1 (in the basic cabinet) or between the 4th and 5th extension units (in the extension cabi- net).

Cabinet thermal load > 350 to 450 W, < 700 W

If the thermal load is between 350/450 W (depending on cabinet ambient temperature) and 700 W, and if 150 W is not exceeded in any extension unit of the cabinet, at least one fan subassem- bly must be provided between the basic unit GE and the 1st extension unit EE1 (in the basic cabinet) or between the 4th and 5th extension units (in the extension cabinet).

A 2nd fan subassembly must be provided if an extension unit is additionally configured with I/O modules such that its heat loss exceeds 150 W. The 2nd fan subassembly must be fitted above the 3rd extension unit EE3 (in the basic cabinet) or above the 6th extension unit EE6 (AS 235, extension cabinet) or above the 7th extension unit EE7 (AS 235 H, extension cabinet).

Standard cabinet with heat exchanger

The standard cabinet with heat exchanger can be operated without an additional fan subassembly if the total thermal load of 350/450 W (depending on cabinet ambient temperature) is not exceeded in the cabinet and if 150 W is not exceeded in any extension unit.

The standard cabinet with heat exchanger is operated with a fan subassembly if the total thermal load is < 700 W and if 150 W is not exceeded in any extension unit. The fan subassembly must be fitted between the basic unit and the 1st extension unit EE1 (in the basic cabinet) or between the 4th and 5th extension units EE4 and EE5 (in the extension cabinet).

If the thermal load in one of the three extension units exceeds 150 W or if the total thermal load exceeds 700 W, a 2nd fan sub- assembly must be fitted between the 2nd and 3rd extension units EE2 and EE3 (in the basic cabinet) or between the 5th and 6th extension units EE5 and EE6 (AS 235, extension cabinet) or between the 6th and 7th extension units (AS 235, extension cab- inet). A maximum thermal load of 1000 W is then permissible.

Configuring values for thermal load

	AS 235
	Basic cabinet	≤ 150 W
	without I/O modules,
	redundant bus connection
	Bus connection, single	- 10 W
	Connected extension cabinet	+ 16 W
	AS 235 extension cabinet without I/O
		0 W
	modules
	AS 235 H
	Basic cabinet	≤ 200 W
	without I/O modules,
	redundant bus connection
￿Bus connection, single		- 10 W
	Connected extension cabinet	+ 8 W
	AS 235 H extension cabinet without	30 W
	I/O modules

Siemens PLT 111 · 1999 3/25