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 Tray Quick 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. “Come and go problems” “Slow down problems” Common EMC 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 Continous tray installation
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 Critical Parameter
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