ElectroMagnetic Compatibility in Cable Tray Systems

1. ElectroMagnetic Compatibility in Cable Tray Systems Ed Cronin, RCDD, President, Cronin Consulting Claes Rosenberg, Export Manager, Defem System/Schneider Electric

2. EMC Research Consortium

3. Definition of ElectoMagnetic Compatibility ”The ability of a device, equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetical disturbances to anything in that environment” Source: 2008 International Electrical Committee (IEC)

4. EMC in the Data Room • The metal cable tray is part of the electrical structure • The metal cable tray is part of the metallic structure • Any metallic structure is known as a “generalized shield”

5. Definition of generalized shield • To function as a generalized shield, the metal does not have to be enclosing the cable. Any continous metal along the cable is a shield. • A shield is any metal structure that is continous and parallel along the cable path

6. Metal Cable TrayQuick Facts • Properly bonded and grounded = ”earth” • Poorly bonded and grounded = ”antenna”

7. Background • July 2007 - EU introduces new EMC directive • It states that any electrical installation shall be made according to ”good engineering EMC practice”

8. EU Directive ...”installer must document that the EMC performance of complete installation is made according to ”good engineering practice” ... Source: EMC Directive 2004/108/EC

9. Common EMC Problems • “Come and go problems” • Lightning strike • on/off transients • radio transmission • “Slow down problems” • Disturbances may force packaged signals to be re-packaged and re-sent

10. Principles of Generalized Shield Equipment Metal structure Cables Differential mode

11. Various Shield Structures

12. Principles of Earth Loop Area Reduction

13. Principles of Earth Loop Area Reduction

14. Principals of Earth Loop Area Reduction

15. Principles of Earth Loop Area Reduction

16. Tray Design • Minor Importance • wire mesh • solid metal tray • perforated metal tray • cable ladder …are all “shield” when properly installed

17. Schneider Electric tests performed with Defem cable tray

18. Ultimate installation Tray directly connected to top of cabinets Floor is Ground Reference Plane.

19. Realistic installation Tray connected with short ground wire to top of both cabinets

20. Possible installation Tray connected with long ground wire to low point of both cabinets

21. Poor installation Tray connected once with a single ground wire to one cabinet

22. Schneider Electric Results

23. Test Conclusions • Single ground connection • Tray connected to one cabinet only • worse than no metal tray at all • creates a disturbance • Continous tray installation • Tray from cabinet to cabinet • best option • not realistic for practical reasons

24. Test Conclusions • Realistic installation • Sort ground wire between tray and all cabinets • clear improvement • Critical Parameter • connection between cable trays and cabinets • continuity of generalized shield

25. Other Conclusions • Source and victim cables at bigger separation distance does not compensate for a badly connected cable tray. It is still contagious…

26. Good Engineering Practices • IEC Standards • To use gasfree and vibration safe joinings of tray, ensuring max 50mΩ • To mark tray joints with a bonding sign • To connect metal cable trays to all cabinets with ground wire, preferrably at cable entrance

27. Good Engineering Practices Place cables as close as possible to parallel earth conductor

28. Good Engineering Practices Additional cables will enhance external shielding effect

29. Good Engineering Practice With multi level cabling, ground wire connection between tray levels

30. Take Away • Properly bonded and grounded = ”earth” • Poorly bonded and grounded = ”antenna”

31. Thank You • Claes Rosenberg – Defem • Ed Cronin RCDD – Cronin Consulting

32. Thank You