Large Cable Size Help

[Darkwing]

I have to install a cable from a new supply meter to an existing DB (no the DB cant be moved or the supply installed closer)
The supply is 400V 3ph 400A
The cable run is 120m long 30m of which is burried the rest of will be clipped direct.
The design current is 280A but may go up to 380-400A in the future.
I have had various suggestions as what cable to use.
185mm single AWA cables
300mm 4 core SWA cable
2x 120mm 4 core SWA cable or even 2x 95mm 4 core SWA

I don't want to use the 300mm as it is difficult to work with.

Any suggestions as to which one is right or are they all wrong.

Thanks

 

[i=p/u]

Zs is one to watch. But get your book out and satisfy yourself.. Not being cheeky.

 

[Richard Burns]

Pity about the 30m buried but then that is what you have.

Any of those options would be OK for the current it just really depends on what you calculate the requirements to be.
You have all the information you need whereas we can only guess at some information and so I would refer you back to I=PU's comment.
Have a look at the books and do the calculations.
Though based on recent threads about parallel supplies it could be interesting.:wink5:

 

[Guest55]

to a certain extent , the CCC of the cable is neither here nor there.
its fairly certain that the sub will be sized to deal with volt drop , which will be considerable for a 400A terminal load thats 120mtrs away , especially if its going to have lighting final circuits at the end.
will it ?
if it will then i'd want a volt drop of no more than 2v at the panel.
and to achieve this will probably mean selecting a cable that far exceeds any current carrying requirements.

and the difference between a nominal Ib of 280A and a potential Ib of 400A at a later date could add considerable cable costs ?

is the client willing to pay for that future expansion capacity of around 40% ?

just some things to consider.
;-)

 

[johnboy6083]

I agree, volt drop will almost certainly be the limiting factor.
whats the power factor of the load, does it have any harmonic content?
if you know the pf, you can use this to alter the volt drop figures. I'd certainly suggest you get reading up, there's a large difference between being told to install something, and designing something to install!
the latter usually means you get the blame!!

 

[Dcf]

Download drakas excellent cable calculator.
It came out at 300mm or 120mm parallel
95mm is pushing the volt drop a bit far.
I dare say more accurate answers can be done by calculation but for a quick reference
I find the app good.....
That's a fair old pull in by the way....better get on the protein shakes that day.

 

[johnboy6083]

You definately need to do accurate calculations, and have them reviewed and signed off by the client, listing any assumptions you made.
if the brown stuff hits the fan, you need proof that you didn't just ask a forum, or use a basic calculator! Also get proffesional indemnity insurance.

 

[Dcf]

Good point on the power factor and harmonic content of connected loads johnboy
as this can alter things big style

 

[Engineer54]

That'll be a parallel cable run then!! lol!!

 

[Darkwing]

Thanks for the help I never considered PF or harmonics.
The load will be mainly lighting as its a feed cable for a sports stadium flood light DB. Approximately 260A for lighting
I have been doing calcs and using software and all 3 options seam ok I was just wondering if anyone had any advice on which is the best to use.
Looking at the volt drop a 2x 120mm 4core will lose 5.71V less than 2%

Some one said to me I cant run single AWA cores that far is this true?

 

[johnboy6083]

Why can't you run AWA that far? For that long a run you'd probably require single point bonding of the armour though.
if this is for flood lighting, I'd refer to the manufacturer for lamp start up data. You could end up in a world of litigation of you underside the cable and lamps drop out when the volts drop!

 

[Knobhead]

You can run AWA but you must run them in trefoil +1 or quadfoil. One end only to be earthed otherwise you will run in to major problems. Therefore a CPC is needed. The mechanical protection needed for AWA is greater. The possibility of sheath damage could render the armouring useless due to corrosion.

You’re best bet is parallel SWA's.

 

[Engineer54]

The first thing you need to determine/decide on, is what loading your going to design this installation for. To me it's pointless to run a cable or cables for 280A, when and if there is more than a good possibility of that load being upgraded to up to 400A in the not too distant future. 400A OCPD's in the way of MCCB's, these can be purchased with adjustable Ir etc, parameters that will cover easily 280A to 400A.