While discussing the cabling aspects of a project, the selection criteria for the right size of interconnecting cables ( 20m long ) became an issue. The list below gives the category and size that I offered. ( Ambient 15 to 40 Deg C and all cables will be laid in fire retardant PVC hoses on the shop floor. Three different hoses will handle power ( 415V AC) , Digital I/O ( 24 V dc) and Analog signal ( 4-20mA) cables.)

1. Power ( 3 Ph.electric motor, full load current 4.9A ) : Multistrand copper cable 2.5 Sq.mm (Rating 1100V and 25A when laid inside a hose)
2. Digital I/O ( max solenoid current 1.28A) : Multistrand copper cable 1.0 Sq.mm x 2 core for each solenoid ( Rating :110V / 7A)
3. Analog Signal ( 4-20mA from pressure and temperature sensor) : 0.25 Sq.mm x 2 core

The customer wants to double the cross section in each of the above case, and says that besides electrical rating, mechanical strength and safety margin also is to be considered. But I feel that my selection is adequate.

Is there any official document or guideline that one can refer to in such instances ? Of course the supplier of the cable can be contacted. But cable manufacturers in India conform to the local "ISI" guidelines and there is no such refernce document in that standard.

Raghu