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Hi All,
Have been reading forums for years now,time came to ask for advice.
Have a job to fit main 3 phase isolator for a shop with flats above.About to 2 nd fix the flats now,when the supply is sorted.There was a single phase to the flats,done some years ago,without any isolators.Now the electricity supplier want one main isolator,another one for the shop and a third one for the flats-all 3 phase.As they didn’t specify what type,I thought to ask here for a second opinion.
As the space there isn’t big(under stairs)
I am thinking to install 4 pole 125 A isolators in a separate enclosure each(BS 60947-3 )
Not the rotary or handle operated isolators.
Advice would be greatly appreciated!

The Ghost

How many flats? I'll guess and say a couple. Three phases could be shared one each to the shop and flats. Not too sure about the DNO dictating on BS7671 territory. I would be asking for the reasoning on that. Think I would inclined to use lewden 60/80/100 amp single phase for each especially as space is limited. So are they expecting three phase meters to the shop and flats each? Doesn't seem to make a lot of sense. They can't dictate the budget for the job!
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Might be a good idea to seek the services of a competent electrician.
  • Thread Starter Thread Starter
  • #4
There are 3 flats above-each will be on its own phase.In theory shared with the shop.
Shop has its own meter and 3 phase fuse board.
DNO does not allow direct share from the 3 phase cutout.Instead they want :
From 3x100 main fuses to go to isolator,then with armoured cable 4x25 mm.sq to Ryefiled box (which is fitted above stairs,due to lack of space).Ryefiled is 7 way-3 for the shop,3 for the flats and 1 for landlord supply.
Then another armoured cable come back down under stairs to 3 red fuse links series 6 ,another isolator for the shop and then to meter and fuse board .
Upstairs from the Ryefiled will go to 4 single phase isolators and meters for the flats and landlord supply.
The only question is what 3 phase isolator to use for main,after the main cutout.
I would use rotary 125 A ,as needs to be lockable,but there is no space.
That’s why would fit 4 pole 125A in a metal enclosure,with lock.
Would Dno object on this isolator and insist on a bigger,commercial type ,with handle ?

As a reply to Wastward10,I am a competent electrical contractor,just this situation is a bit different from what we have been doing until now.
Originally it was agreed with a DNO representative to have a simple sharing of supply from the service cutout through an isolator,then Ryefiled box for the flats,job done.
Turned out ,she wasn’t experienced at all and when their electrician came to pull out the fuses(night time as the shop is William Hill),refused to have this configuration.
So we had a meeting with their boss,who gave his view how everything to be done.
I am only seeking a second opinion here,a reply would be appreciated.


Where is each meter being located?
  • Thread Starter Thread Starter
  • #7
William Hill-existing meter stays under stairs,
For the flats they will be in the flats communal stairs,where the rest is-ryefield box,flats isolators,etc.


Do you have photographs of existing locations please?
The isolator will need to be fused and also large enough to terminate tails and swa..


Is this in London or surrounding area as this seems a standard set up there. Is the service cut out going to be 100A?
I would check if it is not a switched fuse after the cutout as up to the Ryfield unit would only be protected by the cut-out fuse but they seal all this equipment. The main switch fuse/isolator is usually an Eaton/MEM Exel or Glasgow (one of those has smaller dimensions than the other for the same current rating but factor in bending radius of cables inside).
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