Generator Cabling to the Switch Board

Yes, you need to put cables suitable for aleast the maximum current rating of generator, and not the partial load seen by generator.

I would suggest 2 runs of 120 sqmm for each phase if the cables are for 45 deg C ambient and are in free air.

If they are for 55 deg C ambient and are enclosed then you will require 2 runs of 240 sqmm for each phase.

The ambient temperature, cable layout and length of cable make lot of difference in deciding cable size.

Cheers.

"As per calculations each phase should require a 195 mm square cross sectional area". First of all You have to follow the regulations of your country and the class of the ship when deciding the size of the cables and keep in mind that in ships the cables usually has to be bigger than in on shore systems. You also have to consider the length of the cables, space and temperature of the environment. I don´t have the table for cable sizes with me but I believe you will need more then two times 95mm2 for 400Amp.

But If you have an adjustable circuit breaker you can adjust the breaker to fit the cable size that you will use.

Note-All cables in ships has to be with halogen free shield (powerflex is not suitable). And they have to be rated for minimun 440V (welding cables are usualy rated for 50-95V)

When using two or more cables for one phase it is very urgent to take care of that both/all the cables for that phase are of execly the same length to prevent that the shorter cable will carry more amperage.

I hope this will help

Dear Friend,

Your doubt is reasonable. But LLoyds specifications are to be followed. May be they specify double rating. As a thumb rule double rated cables are used, for heat generated will be very less and far below the flash point of diesel fuel oil . This is besides the short circuit rating, calculated along with heat generation while short circuit occurs. It is good for the Chief Engineer. He can sleep peacefully :)

Vijay Saradhi

Ex. Chief (Marine) Engineer,