Using SWA cables in parallel

[Perci]

Hi
A job that I'm currently looking at requires a 300A 3ph supply to a unit. The cable will be 100m long so the calc comes out at 240mm2. This cable is to be pulled down a duct, the main issue is it's weight and size will be a battle. I'm thinking of running two 95mm2 in parallel that would make this job possibly easier. What are everyone's thoughts?

 

[Ian1981]

Hi
A job that I'm currently looking at requires a 300A 3ph supply to a unit. The cable will be 100m long so the calc comes out at 240mm2. This cable is to be pulled down a duct, the main issue is it's weight and size will be a battle. I'm thinking of running two 95mm2 in parallel that would make this job possibly easier. What are everyone's thoughts?

If they where singles you where pulling in I'd say parallel is a good choice but 2 x 95mm can you get them down the duct?
Plus it's two glands to make off and terminate at each end.
Aluminium conductors maybe a better choice.
Or stick with the one cable.
240 mm at 70 degrees operating temp 3 phase is less than 300 amps tho ref method D only gives ambient temp at 20 degrees and that's with out a correction factor of 0.9 to bring it to 30 degree ambient temperature

 

[westward10]

Parallel cables will have a reduced overall csa compared to one cable and are often used for large submains. If your calculations are okay it is the best option.

 

[westward10]

If they where singles you where pulling in I'd say parallel is a good choice but 2 x 95mm can you get them down the duct?
Plus it's two glands to make off and terminate at each end.
Aluminium conductors maybe a better choice.
Or stick with the one cable.
240 mm at 70 degrees operating temp 3 phase is less than 300 amps tho ref method D only gives ambient temp of 20 degrees and that's with out a correction factor of 0.9 to bring it to 30 degree ambient temperature

Two 95.0 better than pulling one 240.0.

 

[Ian1981]

Two 95.0 better than pulling one 240.0.

Depends on the duct that's in I suppose and making sure the cables don't cross and get jammed.
Would rather terminate the one cable even though it's a pig to do.

 

[westward10]

Think one cable will need more washing up liquid.

 

[westward10]

I probably wouldn't duct them just bed them in the ground.

 

[Ian1981]

240mm 3 or 4 core , 3 phase is only 280 amps then using the maximum operating temperature at 70 degrees without applying correction factors

 

[Andy-1960]

And the amount you have to derate by when you run them in a duct can be staggering...

Oh.. and buy a winch, makes life much easier!

 

[Perci]

The duct is 12" so quite large and is completely straight. I calc it with 0.8-pf, ambient temp 20 degrees and on a xlpe at 240mm2. Do you get a different answer?

 

[Ian1981]

The duct is 12" so quite large and is completely straight. I calc it with 0.8-pf, ambient temp 20 degrees and on a xlpe at 240mm2. Do you get a different answer?

Think you've used xlpe at 90 degrees operating temperature and not 70 degrees.
There is a note in the tables making you aware of connecting 90 degree to 70 degree accessories and switch gear.
You need to apply a 0.9 correction factor straight away If cable in a duct or buried as tables give ccc at 20 degrees and not 30 degrees reference method D

 

[Perci]

Ha you just have read my mind Ian! Yes I have done that! I the panel board it is connecting to is quite small so I was thinking the two 95mm2 would be easier to terminate. I was always under the impression that washing up liquid makes the pvc deteriorate?

 

[westward10]

Given the choice I would rather terminate two smaller than one large.

 

[Ian1981]

W

Ha you just have read my mind Ian! Yes I have done that! I the panel board it is connecting to is quite small so I was thinking the two 95mm2 would be easier to terminate. I was always under the impression that washing up liquid makes the pvc deteriorate?

well never poured it on cables so I don't know haha.

 

[Perci]

Dpes anyone know what factoring is applied for parallel supplies? I think the CSA normally works out less that with one cable

 

[Darkwood]

Regardless of this been 1 or 2 cables, the task of trying to pull through an 100m duct even at 12" is going to be a massive challange, the weight alone plus the friction are going to make this a hard job, I would have trenched and buried such a cable(s) run ...good luck on it!

 

[Ian1981]

Dpes anyone know what factoring is applied for parallel supplies? I think the CSA normally works out less that with one cable

You may have to apply grouping factors as well for cables in parallel

 

[Perci]

Yea we were asked to have a look at the job after they put all the ducts in roads down etc. The joy!

 

[Ian1981]

Yea we were asked to have a look at the job after they put all the ducts in roads down etc. The joy!

Nightmare!!

 

[westward10]

Have you tried sizing it with three cables. Another thought does the armour have to support main protective bonds upstream.