T
The Ghost
Yeh that makes sense, OP did say that.Fit a switch fuse disconnector.
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
Yeh that makes sense, OP did say that.Fit a switch fuse disconnector.
Well if it's in the regs, then it's in black and white....just seems maddnes having a good earth at the DNO cutout, then at the DB end ditching it and then put in earth rod. Again , the University has several of its own substations with massive section boards that feed other large buildings (so technically the substation is the DNO supply) so then there'll be say 3 or 4 300mm2 SWA cables go out to feed other buildings, no separate cpc, then when they enter the building, an earth conductor is took off the armour to an earth bar and then from that you'll have a main protective conductor to the buildings section board, and protective earthing conductors to other services.I think this comes from Reg 543.4.1
The armour of those cables may be adequate to support bonding.Well if it's in the regs, then it's in black and white....just seems maddnes having a good earth at the DNO cutout, then at the DB end ditching it and then put in earth rod. Again , the University has several of its own substations with massive section boards that feed other large buildings (so technically the substation is the DNO supply) so then there'll be say 3 or 4 300mm2 SWA cables go out to feed other buildings, no separate cpc, then when they enter the building, an earth conductor is took off the armour to an earth bar and then from that you'll have a main protective conductor to the buildings section board, and protective earthing conductors to other services.
Ah so smaller SWA cables may not be suitable for that. Funnily the cables I've seen used in this way were much bigger that 35mm2, 50mm upwards if I remember correctly.The armour of those cables may be adequate to support bonding.
Well I suggest you get a pet rat and train it to run through drain pipes with string tied to it, put it through your duct, then tie a rope to the string, then use rope to pull in earth cable.....job donethanks for comments guys , i need all phases as massive house with a lift and various kitchens with big appliances etc , but i guess the main switch being 300ma rcd then me using 30ma rcbo units is the way , there is a 6 inch duct howeve its not a straight route and they didnt pull in a draw wire just the cable (bless them )
I'm guessing DNO can supply an earth to a quality level they feel is ok, but within the installation Table 54.8 would say it needs 50mm copper, which is about 400mm steel. And 4 core 300 is about 320mm steel, so it wouldn't pass muster. Unless I'm talking rubbishthe University has several ... substations ... so then there'll be say 3 or 4 300mm2 SWA cables go out to feed other buildings, no separate cpc, then when they enter the building, an earth conductor is took off the armour to an earth bar and then from that you'll have a main protective conductor to the buildings section board, and protective earthing conductors to other services.
I have a method for solving this problem, I've used it a few times now. It involves a Henry, a ball of string and a couple of Tesco bags. Give it a goWell I suggest you get a pet rat and train it to run through drain pipes with string tied to it, put it through your duct, then tie a rope to the string, then use rope to pull in earth cable.....job done
Unless the RCBO's are double pole or single pole switched neutral then you don't want an upfront time delayed RCD. In your situation I would do as @westward10 says and use the PME for the distribution circuit, Ditch it at load end and make the house TT. Adequately support the tails so there is zero chance of them moving etc and use a four pole main switch incommer kit and RCBO's.thanks for comments guys , i need all phases as massive house with a lift and various kitchens with big appliances etc , but i guess the main switch being 300ma rcd then me using 30ma rcbo units is the way , there is a 6 inch duct howeve its not a straight route and they didnt pull in a draw wire just the cable (bless them )
Where did you get that it has to be equal to the supply conductors from? Why doesn't armour "cut it" as a reliable earth? So what happens to the 300mA time delayed RCD in the event of a neutral-earth fault on one of the final circuts protected by an RCBO?PME earth when taken outside of equipotential zone of origin has to be equal to supply conductors. Steel Wire Armour simply doesn’t cut it as a reliable earth. So totally agree use SWA to protect the feeder cable glanded and terminated to DNO earth. I would be tempted to run it through a 300mA time delayed rcd as mentioned above. Install it in insulated enslosure at house with a TT rod or 2 and have every circuit on 30mA rcbo’s. It’s your only option other than digging it up and installing separate earth.
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