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Jim Ingram
 
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Default ring mains - balancing load

Hi,

Could someone please expain to me what the requirements are for
ensuring a balanced road on a ring main.

As part of some minor building work I'm planning to install a new
ring main for the kitchen. As is often the case dishwasher and
washing machine are next to each other and would be relatively close
to the start of the ring. I would estimate about 4 m in from the cu
with a total length of circuit of around 17m. If the two appliances
were on together this might be around 6.5 kW giving a current of 27A
of which I estimate 76% would travel down the shorter leg. This would
be getting fairly close to the cables capacity. An additional load
near this point could take the cable to above its rating (~24A for
2.5mm2) and not trip the 32A mcb. I would have thought this situation
to be just about acceptable, as at least some of the loads will be
fairly short lived (minutes rather than hours).

Alternatively I could lose some cable under the floorboards to
lengthen the tail or put the wm/dw on a separate radial circuit.

The existing ring main is much much worse - serves the whole house
with a potential load of 40 A (helped by an illegal spur) at the
second socket 7m from cu on a 70m ring circuit! not good.

Thanks

Jim