ElectroMagnetic Compatibility in Cable Tray Systems Ed Cronin, RCDD, President, Cronin Consulting...
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Transcript of ElectroMagnetic Compatibility in Cable Tray Systems Ed Cronin, RCDD, President, Cronin Consulting...
ElectroMagnetic Compatibility in Cable Tray Systems
Ed Cronin, RCDD, President, Cronin Consulting
Claes Rosenberg, Export Manager, Defem System/Schneider Electric
EMC Research Consortium
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)
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”
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
Metal Cable TrayQuick Facts
• Properly bonded and grounded = ”earth”
• Poorly bonded and grounded = ”antenna”
Background
• July 2007 - EU introduces new EMC directive
• It states that any electrical installation shall be made according to ”good engineering EMC practice”
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
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
Metal structure
Equipment
Cables Differential mode
Principles of Generalized Shield
Various Shield Structures
Principles of Earth Loop Area Reduction
Principles of Earth Loop Area Reduction
Principals of Earth Loop Area Reduction
Principles of Earth Loop Area Reduction
Tray Design
• Minor Importance– wire mesh – solid metal tray – perforated metal tray– cable ladder
…are all “shield” when properly installed
Schneider Electric tests performed with Defem cable tray
Ultimate installationTray directly connected to top of cabinets
Floor is Ground Reference Plane.
Realistic installationTray connected with short ground wire to top of both cabinets
Possible installationTray connected with long ground wire to low point of both cabinets
Poor installationTray connected once with a single ground wire to one cabinet
Schneider Electric Results
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
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
Other Conclusions
• Source and victim cables at bigger separation distance does not compensate for a badly connected cable tray. It is still contagious…
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
Good Engineering Practices
Place cables as close as possible to parallel earth conductor
Good Engineering Practices
Additional cables will enhance external shielding effect
Good Engineering Practice
With multi level cabling, ground wire connection between tray levels
Take Away
• Properly bonded and grounded = ”earth”
• Poorly bonded and grounded = ”antenna”
Thank You
• Claes Rosenberg – Defem
• Ed Cronin RCDD – Cronin Consulting
Thank You