Discuss Ze on a SWA in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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nicsin02

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Hi guys, i am testing a 3-phase D/B tomorrow and its supply is only a 4-core cable so its earth comes from the Gland-frying pand and then a flying lead to the earth bar, normally doing domestic property i would disconnect earth for Ze ensuring no parralell paths, what would be the norm on this occasion? thanks guys
 

telectrix

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same procedure but measure o each of the phases. reconnect earthing conductor for PFC reading. ensure installation is isolated before dissing earth. if it's a sub-board, the EFLI is noted as Zdb
 
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nicsin02

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so do i have to take the lock-nut off and disconnect the gland to make sure no paralell paths?
 

telectrix

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is the SWA glanded into a metal CU or an insulated one?
 
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DurhamSparky

just remove any bonding cables.... and clip on to rail.... f its a PIR put it down as a limitation...!

if you take gland off and damage it putting it back on or damage teh strands it will be hell to fix..!
 

telectrix

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in that case, i would disconnect any bonding conductors and the fly lead. i might get shot down , but i would prefer that to the possible risk of compromising the integrity of the glanding by disconnecting . apart from the risk of having 3 live phases flopping about unglanded.

- - - Updated - - -

beaten to it by torpedo fingers. GRRRR>
 

telectrix

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must be getting old. bloody heart attack slowed me down. making a good recovery now i'm back on a few beers, though.
 

needasparks

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If this is a swa feed would this mean it is a sub-board or a feed from a switched fuse as in both cases its not a Ze but a Zdb (Zs).
Its not normal to have a swa feed in the usual sense of a supply without it going through another device.
 
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nicsin02

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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?
 

needasparks

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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?
No you are correct but this is downstream from the mains so no need to remove any earthing just isolate before testing.
 
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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.:smile:

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.
 
E

Engineer54

Actually, you're wrong.:smile:

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.....
 
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