Using SWA cables in parallel

[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.

 

[Ian1981]

Was going to say are you installing a separate cpc (half the line conductor using table 54.7) or using armour as cpc?

 

[bigspark17]

What is this supplying? With the info above id lean twoards 2x 95mm 4c

 

[Ian1981]

What is this supplying? With the info above id lean twoards 2x 95mm 4c

Each cable needs the appropriate correction factors applying first before adding together if using in parallel. volt drop and making sure zs is low enough for the protective device needs considering also.

 

[Perci]

There will be a separate cpc installed to achieve the maximum Zs for the mccb. The supply is for a unit that will be effectively rented so no idea what sort of load it will be.

 

[Ian1981]

There will be a separate cpc installed to achieve the maximum Zs for the mccb. The supply is for a unit that will be effectively rented so no idea what sort of load it will be.

Do you know the mccb max zs from manufacturer, as this may be the big influencing factor to what size cable(s) you need to install as 100meter run and 300 amp supply is rather large.

 

[bigspark17]

Have you already taken a Ze at mccb panel board.? What is the max zs you need to meet.?

 

[Perci]

The Ze was 0.09 I'll have a look when I get in the office buts it's a 400A Square D MCCB set at around 0.8 mulitiplyer to give 300A I have a feeling it was 0.37

 

[Ian1981]

The Ze was 0.09 I'll have a look when I get in the office buts it's a 400A Square D MCCB set at around 0.8 mulitiplyer to give 300A I have a feeling it was 0.37

You need to apply a tolerance of +20% using a mccb for max zs giving a multiplier of 1.2
See beama guide to low voltage circuit breaker standards.
It's a good download to give good guidance.

 

[Perci]

What's the tolerance of 20% for? I'm really thinking the 2x 95mm are going to be a lot easier than a 300mm2

 

[Ian1981]

What's the tolerance of 20% for? I'm really thinking the 2x 95mm are going to be a lot easier than a 300mm2

It's the tripping characteristic of the device.
Manufacturers may state lower tolerances that's why it's best just to ask the manufacturer