Cable calcs

[Mr s]

Good Evening Gentlemen,

Please bare with me as I have looked at previous posts and some people have asked similar quistions and got slated for it...

I am wiring an office, it's on the fourth floor of a multi story building! I need to run two supply's to comms cabinets inthe basement. The cable run is under a raised floor so in free air really clipped to the floor! It then jumps into a riser down to the basement on basket on its own again. The overall run is 89 meters my employer seems to think 6mm swa will be fine. And I just wanted to check... I have not worked these figures out in a while but come to the conclusion that I will have 10.39v in my volt drop and rating factors ca = 1. Cg=1. Cf=1. =3 16amp 60898. 16 divide by 3 = 5.33

So could you please guid me whether I am on the right tracks or and if my cables selection is right.....

Many thanks

 

[davesparks]

1 x 1 x 1 = 1

 

[telectrix]

need to know the design current.

 

[Richard Burns]

The PD current has been used here to calculate the volt drop.

But as Davesparks says it is not divide by 3 but by 1 to give a tabulated value of 16 A or less.

6mm² SWA will just about cope with that!

So volt drop OK, current carrying capacity OK.

 

[Darkwood]

Id be more concerned about the earthing arrangement here been a comm's supply... upgrading the SWA to 4core and larger csa could allow for an extra core to meet the requirements of the functional earthing....

Thats if it is what I think it is?

It be an expensive error to forget the requirements for functional earthing ... again if it is required --- info needed!

 

[Mr s]

Thanks for the reply's people....

I am gaining access to the comms room tomo so will check the earthing arrangement, but when ever I install power to comms cabinets I run a clean earth back to the incoming earth bar!

Many thanks