Minimum Voltage at incoming supply point

normally, but not in a few very old roads originally wired for DC, the houses will share along the phases 1,2,3,1,2,3, and repeat..


Round here (SSE, the southern bit - other DNOs will vary, and realise that cities are something else again)


For a half megawatt transformer on the ground of the kind found in a fenced compound at the end of the road, there may be 70 houses per phase or more like 50 if there are also a few shops and things that take a 3 phase supply from the same transformer.

You might think 400A per phase, = 400* 3 * 230 = 270KVA, and on a 500KVA unit  in practice you may see two branches going off from each phase fused at 400A each.  (so yes, 25- 35  houses on 400A fuse)

Anything much less than 400A would not always discriminate well with 100A downstream once things are loaded up.



For a suburban housing estate, larger -say 1MVA plus -  transformers make little sense, as the length of the LV to cover all the properties is voltage drop limited. So,  two smaller units a few hundred yards apart are more economic , 11kV line is cheaper than the weight you would need to go a long  way at LV.

High rise blocks however may have enough users to need most or all of a transformer each, and then larger transformers and still quite close together, make more sense.

Spread out rural has the reverse - with a low rated pole pig  for each cluster of buildings that are within transformer sharing distance, and 11kV yompoing over the fields.

Very very  spread out (only seen in Scotland, but maybe used elsewhere) it becomes worth having 33kV phase to phase, rather than 11kV,  and then the 33k-400V transformer at the last pole before the village.

normally, but not in a few very old roads originally wired for DC, the houses will share along the phases 1,2,3,1,2,3, and repeat..


Round here (SSE, the southern bit - other DNOs will vary, and realise that cities are something else again)


For a half megawatt transformer on the ground of the kind found in a fenced compound at the end of the road, there may be 70 houses per phase or more like 50 if there are also a few shops and things that take a 3 phase supply from the same transformer.

You might think 400A per phase, = 400* 3 * 230 = 270KVA, and on a 500KVA unit  in practice you may see two branches going off from each phase fused at 400A each.  (so yes, 25- 35  houses on 400A fuse)

Anything much less than 400A would not always discriminate well with 100A downstream once things are loaded up.



For a suburban housing estate, larger -say 1MVA plus -  transformers make little sense, as the length of the LV to cover all the properties is voltage drop limited. So,  two smaller units a few hundred yards apart are more economic , 11kV line is cheaper than the weight you would need to go a long  way at LV.

High rise blocks however may have enough users to need most or all of a transformer each, and then larger transformers and still quite close together, make more sense.

Spread out rural has the reverse - with a low rated pole pig  for each cluster of buildings that are within transformer sharing distance, and 11kV yompoing over the fields.

Very very  spread out (only seen in Scotland, but maybe used elsewhere) it becomes worth having 33kV phase to phase, rather than 11kV,  and then the 33k-400V transformer at the last pole before the village.