Practice exam papers hardest question

[R32]

Can anybody help me find the best place to start when tackling a question like this?

Ex Q1: An immersion heater rated at **, ** kW is to be installed using **** sheathed cable. The circuit will be fed from a ** , and will be run for much of its length in the roof space which is thermally insulated with glass fibre. The roof space temperature is expected to *** and where it leaves the consumer unit and passes through a **, the cable will be bunched with others. Calculate the cross-sectional area of the required cable and the anticipated voltage drop using IEE wiring regulations.


Quite unsure for the most part and especially the voltage drop.

Any hep wold be much appreciated

Regards

 

[telectrix]

work out the current from **watts/230v. Ib= **.

work out the derating for ambient temp, bunching, and thermal insulation, say that comes to **, then you need a cable size that will carry **without derating.

once you have selected the cable size, you can work out the volt drop. VD= (mV/A/m x L x I)/1000

 

[Guest123]

Start by finding your factors in BS 7671.

You have 3 in that example, ambient temperature (Ca), embedded in insulation (Ci) and grouping (Cg).

 

[Spudnik]

Values edited at the request of the OP