Do Cable Trays in Sydney Car Parks Require Individual Earthing?

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Discussion Overview

The discussion revolves around the requirements for earthing cable trays in a car park in Sydney. Participants are exploring the extent of earthing needed for galvanized cable trays that are joined together, considering local electrical codes and standards.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on whether each 3m length of cable tray should be individually earthed, or if earthing can be limited to one tray at each run end.
  • Another participant notes that there are various "standard" earthing practices globally and emphasizes the importance of consulting local electrical codes.
  • A third participant suggests that the type of cable used may influence earthing requirements and references an external discussion for further insights.
  • One participant mentions that Australia follows IEC standards for electrical installations, specifically referencing IEC 61537 and its current status regarding protective earth functions.
  • Another participant discusses NEMA standards from the USA, indicating that metallic cable trays can be bonded to the building's metal frame for grounding purposes and notes changes in recommendations over time regarding bonding intervals.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the earthing requirements for the cable trays, with multiple competing views presented regarding the extent and methods of earthing.

Contextual Notes

The discussion highlights the dependence on local electrical codes and standards, as well as the potential influence of the type of cable used, which may affect earthing practices.

Futsal1st
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I am looking at a building with a car park in Sydney. Electrical circuits are run on perforated cable trays at high level.

I understand that the trays require earthing, however, I'm trying to determine the extent.

The trays are made from galvanized sheet and come in 3 meter lengths and are butted to each other. Two short straps (around 100mm long), one on each side, are used to join the lengths together. 10mm bolts and nuts are used for the connection.

Should the trays be individually earthed or only one at each run end or some thing in between? I have been told by one contractor that one Earth per tray is adequate. I've been told by an electrical engineer that each 3m length of tray should be individually earthed.

Advice please ..

Thaks
 
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There are hundreds of "standard" earthing practices around the world. There is no universal answer. You must consult your local electrical codes. It is not only wise, but probably legally mandated that you do so.
 
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In my opinion, Australia use IEC standards for electrical installations.
IEC 61537 Annex C Protective Earth [PE] function.
But -as far as I know- no Annex C is detailed still. It is "under consideration".

In U.S.A. NEMA VE 2-2013
3.8.1 Cable Tray Used as an Equipment Ground Conductor (EGC)
3.9 BONDING TO THE METAL FRAME OF THE BUILDING AND EARTH

Metallic cable trays are permitted to be bonded to the metal frame of the building and Earth for signal grounding (“noise” prevention). This may be desirable if the cable tray system is not inherently bonded (connected) to the metal frame of the building and Earth through metallic support systems.

NEMA VE-2 2001 Edition recommended all 60 feet .From 2006 there is not any recommendation of the bonding interval.

The grounding bonding methods are stated in NEC[2017] Art.250.8
250.8 Connection of Grounding and Bonding Equipment. (A) Permitted Methods.
 
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