A new Safety and Health Information Bulletin, published by the U.S. Department
of Labor Occupational Safety & Health Administration (OSHA), describes the
hazards of overloaded cable trays and identifies specific requirements to help
avoid those hazards.

The purpose is to:

• Review the proper methods for safely installing, maintaining and inspecting
  electrical cable trays;


• Provide information regarding the hazards of overloaded cable trays;


• Identify specific Occupational Safety and Health requirements that address
  the proper installation and maintenance of cable trays;


• Recognize electrical cable tray misuse that can lead to electric shock and
  arc-flash/blast events and fires caused by overheating.

Cable trays can provide a safe component of a wiring distribution system.
However, if not designed and installed properly, wiring inside cable trays may
pose hazards such as fire, electric shock and arc-flash blast events. During
the maintenance, installation and inspection of cable trays, the following
concerns should be taken into consideration.

• Where cable trays pass through fire-rated partitions, walls and floors,
  appropriate fire stops should be provided to prevent the spread of a fire or
  the by-products of combustion.


• Cable trays in hazardous locations must only contain the wiring permitted in
  such locations.


• Cable trays must be properly supported in accordance with the installation
  instructions. Overloading cable trays can lead to a breakdown of the tray, its
  connecting points and/or supports, causing hazards to persons underneath the
  cable tray and even leading to possible electric shock and arc-flash/blast
  events from component failure when the cables are suddenly no longer supported.


• When cable trays are overfilled, excessive heat build-up in and around live
  conductors can cause the insulation to break down, leading to potential shock
  hazards or fires.


• The fill values for cable trays specified in the 2005 NEC range from a single
  layer to roughly a 50% fill of the cross-sectional area of the cable tray.


• When cable trays are overfilled beyond the fill criteria established by the
  NEC, add another cable tray system above, below, or next to the overfilled
  tray. Allow enough working space around the added cable tray.


• Grounding of cable tray systems is essential for personal safety and
  protection against arcing that can occur anywhere in the wiring system. Proper
  grounding must be done before cables are installed and tested before cables are
  energized.


• Abandoned cables within cable trays should be removed.

More info

AplusA-online.de - Source: U.S. Department of Labor - Occupational Safety & Health Administration