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 Tray Quick 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

“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

Principles of Generalized Shield Equipment Metal structure Cables Differential mode

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

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

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

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

Schneider Electric Results

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

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

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