Siemens SIMATIC NET PROFIBUS manual Conditions, Clearance Table, How to Read the Table

Installing LAN Cables

Conditions

Grouping cables according to voltage classes assumes that the interference voltages relate directly to the power supply voltage conducted (the lower the supply voltage, the lower the interference voltage). Remember, however, that DC or 50 Hz power supply voltages do not represent any danger to PROFIBUS cables. The critical interference voltages in the kHz to MHz frequency range are created by the “consumer” connected to the cable. A 24 V DC cable with which a relay is switched regularly has a far more critical interference range than a 230 V cable supplying a light bulb.

In the information shown below, it is assumed that all the components within an automation system and all the plant components controlled by the system (for example machines, robots etc.) at least meet the requirements of the European standards for electromagnetic compatibility in an industrial environment. If devices are defective or incorrectly installed, higher interference voltages must be expected!

The following is assumed:

SThe cables for analog signals, data signals and process signals are always shielded.

SThe distance from the cables to the chassis surface of the system (cabinet wall, grounded cable channel, ...) is not more than 10 cm.

Note

In general, the greater the distance between cables and the shorter the distances over which the cables run parallel to each other, the less the danger of interference.

Clearance Table

Table C-1 contains the general rules for clearances between a variety of cables. The rules should be understood as minimum rules for positioning LAN cables within buildings (inside and outside cubicles).

How to Read the Table

To check how cables of different types must be laid, follow the steps outlined below:

1.Find the cable type of the first cable in column 1 (cables for ...).

2.Find the cable type of the second cable in the relevant section in column 2 (and cables for ...).

3.Read the guidelines for laying the cables in column 3 (lay ...).

C-14	PROFIBUS Networks SIMATIC NET
	6GK1970-5CA20-0AA1 Release 2 05/2000