Discuss PME head , builder forgot earth cable , 100amp 3phase supply , 10 bedroom house , 10 bedroom house in the The Welcome Forum area at ElectriciansForums.net
Hi all , im new here but have always looked for answers over the months
description of my question
there is an external 100 amp 3 phase metered head that this new 10 bed house is to be fed from , the builders installed a 35mm 4core swa as i directed however they forgot about a 16mm earth
now is my only option to treat this a a tt supply or a really stupid question is can i simply make it a pre from the neutral at my distribution board (as it would be the same as whats at the source ) obviously not but it would definatly be easy
now over the last 20 or so years i have not ever done a tt supply (not since collage anyway) do i need to drop earth rod then cover the new 3phase dis board with a 30 ma main switch or can i install 100ma main switch and then protect all circuits with planned rcbos as original plan
also one more thing , was i right in thinking that i was never allowed to take the earth from the pme head regardless to if the builder had remembered the earth ?
Ive seen loads of buildings done this way, example: University colleges, the main building will have the incoming supply to a large section board and its own earth bar for water, gas etc, then SWA cables feed the other accommodation buildings to their own section boards and earth bars ...no separate earth conductor.
You did say it is a PME supply? So why not use the terminal at the cut-out??? Sorry if I missed something. What or where is the 35mm² SWA coming from and to and how far?
Kev 1 N , i covered this issue of using the steel wired as main earth resonantly within a 5 yearly of an office block as after calling the NICEIC help desk and then covering it on my last yearly visit was told the earth cable required if your earthing main water or steel work gas etc etc (he even handed me a few A4 sheets on it ) (the know it all lol)
Vortigern , 4 core 35mm swa from main supply head , its about 35meter stretch (under block paving and slabs not an easy route ) and when you say cut off do you mean at the main switch at the planned new dis board within the house ?
You did say it is a PME supply? So why not use the terminal at the cut-out??? Sorry if I missed something. What or where is the 35mm² SWA coming from and to and how far?
Just out of interest (maybe should start a new thread but after being on here for months still can't work out how), is the steel in SWA manufactured to be the correct ratio csa to the cores, bearing in mind it has a higher resistivity etc? Don't know why I have just thought about this but I have blindly used the armour as a cpc before without checking this!
Ok now I see you can't retrospectively (easily) come from the pme terminal at the main service head (cut-out) But I don't get how you can join SWA into the main cut-out. What about the gland etc. Just ignore me if you think that is dumb. You can even give me a dumb rating I'm a bit short on them.
The easiest thing is to create a TT system at the house. Use the PME earth for the swa cable supply then at the house end gland it off in an all insulated enclosure to separate the PME earth from true earth. Fit rcbos to each circuit.
Reply to PME head , builder forgot earth cable , 100amp 3phase supply , 10 bedroom house , 10 bedroom house in the The Welcome Forum area at ElectriciansForums.net
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