Sizing power cables part installed in ducts

[Andy-1960]

Anybody help with the sizing of power cables when the cable is part run in a duct.

The supply in question is 630A, so it makes a big difference!

If the cable run is 40m where 8m is in a duct, do you have to rate the cable as if it was in a duct for its entire length?

The supply in question is 630A, so it makes a big difference!

Cannot seem to find any information on this anywhere.

 

[buzzlightyear]

what are you loading!

 

[Andy-1960]

what are you loading!

Sub-distribution board in a factory

 

[buzzlightyear]

Anybody help with the sizing of power cables when the cable is part run in a duct.

The supply in question is 630A, so it makes a big difference!

If the cable run is 40m where 8m is in a duct, do you have to rate the cable as if it was in a duct for its entire length?

The supply in question is 630A, so it makes a big difference!

start again .what type of cable is it swa or string .or do you read the regs?

 

[Pete999]

start again .what type of cable is it swa or string .or do you read the regs?

Buzz, not sure if the OP has any Electrical experience, nothing listed in his profile anyway.

 

[Andy-1960]

start again .what type of cable is it swa or string .or do you read the regs?

Not really called for is it!

 

[buzzlightyear]

Not really called for is it!

where do I start andy-1960, it is no point giving us part of a story .

 

[Andy-1960]

Cable is XLPE/SWA/PVC run on ladder for the majority of the run, dropping down into a duct for about 8 metres. Feed is to a sub-main distribution board, fed from a Schneider NSX630A MCCB with a micrologic 2.0 trip block.
I have run this thru our Amtech (now Trimble software) but it does not give the option for a part of the run to be in a duct.. all or nothing!
I was just asking for opinions..

 

[Strima]

You either design it for the worst installation method or use two different cable sizes for the two installation methods.

All boils down to cost, ease of installation and maintenance.

 

[buzzlightyear]

Cable is XLPE/SWA/PVC run on ladder for the majority of the run, dropping down into a duct for about 8 metres. Feed is to a sub-main distribution board, fed from a Schneider NSX630A MCCB with a micrologic 2.0 trip block.
I have run this thru our Amtech (now Trimble software) but it does not give the option for a part of the run to be in a duct.. all or nothing!

is this a job planning or theory ?

 

[Andy-1960]

Planning

 

[Andy-1960]

You either design it for the worst installation method or use two different cable sizes for the two installation methods.

All boils down to cost, ease of installation and maintenance.

Thanks for getting back to me.

I have always sized it for worst case but cable size near enough doubles when you stick it in the ground I just wanted to bounce the question in case I was missing something..

 

[Strima]

Take a look at table 4B4, software often does not take into account various depths you can go to and the appropriate rating factors.

Does it have to be in duct?

 

[davesparks]

Unless you are going to use different sized cables for each part of the run then you have to size the whole cable according to the worst conditions it passes through.

Are you planning to run a single cable or multiple cables in parallel?

 

[westward10]

Yes you plan for the worse case regardless of the length.

 

[westward10]

Parallel cables whether two or three of them maybe the best option as you will get a reduced overall csa.

 

[Bobster]

Is this going to be a parallel cable install? Usually cheaper and easier. Plus use smaller cables.

 

[Ian1981]

Would imagine its reference method D in the tables then do your correction factors Cs,Cc,Cd and whatever else is appropriate

 

[Andy-1960]

Yes you plan for the worse case regardless of the length.

I thought this was the case and have always done it this way, but in this scenario it just jumped out that 32m is in free air and 8m is in the duct.

 

[Andy-1960]

Is this going to be a parallel cable install? Usually cheaper and easier. Plus use smaller cables.

Yes, it's going to be two in parallel, it will certainly be easier!