Electrical Device Rating Question

I too have the same doubt because it is said that 10% rise in voltage reduce life of a bulb to half of its actual duration.

Our voltage is rated at 240V with + 15% due to our voltage frequency from 50 to 55 hz.

On a 240v network, there will typically be some voltage drop from the service through the wiring to the motor, which will then receive ~230v, and is rated accordingly.

In any distribution network, the voltage will rise and fall within a tolerance band. As far as any particular device is concerned, 230V and 240V are in the same tolerance band, so the absolute rating of the device doesn't matter; it won't blow up if the voltage now is 230.0001V!

Most electrical equipment can operate satisfactorily within a range of supply voltages, usually wider than plus or minus five percent about its nominal utilization voltage. But the fact that equipment will fuction over a particalur range of voltage does not mean that it will function well at the extreme ends of that range.

A transformer's name plate voltage is 433V (i.e.) it is its open circuit voltage. But, when you load the transformer to its rated capacity, there will be some voltage drop inside the transformer (in the transformer secondary windings). Now, you will get only around 415V at the transformer terminals itself. Add to this, the voltage drop in the cables from the transformer to the distribution boards and from the distribution boards to the loads (under rated load conditions). The single phase voltage would not go beyond 230V under normal circumstances. That's why single phase equipments/devices are rated at 230V.