voltage drop

Hi, Our house has modern wiring, it also has a new metal Consumer Unit, with a split rail, 2 x RCD and SPD. The house has 2 lighting circuits, Ground Floor and First Floor. All the bulbs in the house are LED, but some are better quality LED bulbs and four of the bulbs are cheap large...

This morning I was using our electric shower (Triton Enrich, 8.5 kW, 6 years old) when it virtually stopped. The flow reduced abruptly to a trickle, without a change in temperature, the on-light stayed on. I switched it off immediately. I ran a cold-tap to test the water supply but it was fine...

Was reading an article on IET about whether it is permissible to exceeded the voltage drop limits in certain situations. Thus to further expanded the original question on IET; would it ever be acceptable if one exceeded the 5% voltage drop for power circuits / 3% voltage drop for lighting...