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Discuss Hazardous areas - control voltage transformer earthing - in the Industrial Electrician Talk area at ElectriciansForums.net

Shweblet

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I've been in an ongoing debate regarding earthing of a control transformer and i'd like some other opinions.

690 primary, 120v secondary supplying control circuits (contactors/DC convertors etc), the neutral is tied to earth - My issue is the location that it is tied to Earth.

As far as I know the difference between a TN-S and a TN-C-S system is whether or not the neutral is connected to 'ground' at the source or further down the line.

60079-14 - 6.3.2 TN type of system earthing If a type of system earthing TN is used, it shall be type TN-S (with separate neutral N and protective conductor PE) in the hazardous area, i.e. the neutral and the protective conductor shall not be connected together, or combined in a single conductor, in the hazardous area. At any point of transition from TN-C to TN-S, the protective conductor shall be connected to the equipotential bonding system in the non-hazardous area.

Please see attached photo; The proposed design shows the point where the neutral is tied to earth (circled in blue) - this makes the highlighted section the 'C' in a TN-C-S system.

To create a TN-S system it would need to be where it is marked Red (taken directly off the transformer)

Also the highlighted cable is a line bushing from an Exd enclosure (which houses the transformer) to a close coupled Exe enclosure so this bushing cable would be combining the neutral and protective conductor.

Any thoughts agreeing/disagreeing? I can't seem to budge some peoples stance on it and to me it's black and white.

Cheers.
 

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