Isolation - Siemens SIMATIC TI525 Hardware And Installation Manual

APPENDIX B – GROUNDING GUIDELINES
B.4.2.2

Isolation

The second approach to handling noise problems is to isolate the problem device
and its wiring from the electronics and associated signal wiring. You may
accomplish this by increasing the physical distance from some types of noisy
devices. For extreme cases, electrostatic (metal) shielding may be required.
This is true for noise sources outside as well as inside the mounting cabinet
(NEMA-type recommended).
Two cases of field wiring warrant special attention: Wiring which enters the
harsh-noise area to enable monitoring and control of those devices, and TTL or
low-level (less than 24 V) wiring. In these cases, supplement the physical
separation between control and noise-prone wiring with shielded, twisted-pair
wiring (12 twists/ft) for the control signals.
Ground the shield at the electronics side only to the single-point ground.
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Hardware and Installation User Manual
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