Ze on a SWA

[DurhamSparky]

I joined the NAVY to feel a man!!!

 

[WayneL]

yeah its a sub mains fed from another board, i know its a Zdb but would still have to fill it in the Ze section for the new sub board or am i wrong lol?

Actually, you're wrong.

It's Zs of the sub-main and you don't disconnect anything to measure it.

The only place you measure Ze is at the origin of the installation - and for this you disconnect the 'Earthing Conductor'.

What you are talking about disconnecting is the CPC of the SWA (Sub-main)..........and for a Zs measurement this is left connected.

If, on the other hand, your 3 phase board had it's own 'earthing system' (e.g. a seperate earth rod), then you could treat it as a seperate installation, with it's own origin and 'earthing conductor'..........then you could measure Ze at your board.

 

[Engineer54]

Actually, you're wrong.

It's Zs of the sub-main and you don't disconnect anything to measure it.

The only place you measure Ze is at the origin of the installation - and for this you disconnect the 'Earthing Conductor'.

What you are talking about disconnecting is the CPC of the SWA (Sub-main)..........and for a Zs measurement this is left connected.

If, on the other hand, your 3 phase board had it's own 'earthing system' (e.g. a seperate earth rod), then you could treat it as a seperate installation, with it's own origin and 'earthing conductor'..........then you could measure Ze at your board.

Completely agree, you will be measuring nothing but the Zs at a sub-distribution board.

At the main incoming position of that sub-board, your value can be stated as Zdb, and can be noted no doubt in the Ze position of your certificate for this sub-board, with a an explanation in the remarks column. The rest of the sub-boards circuits, will again be tested as normal for Zs values.....