IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Which installation method 117 or 118?
Topic Summary:
Created On: 08 November 2017 12:25 PM
Status: Read Only
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 08 November 2017 12:25 PM
User is offline View Users Profile Print this message



Stuz

Posts: 5
Joined: 19 May 2016

Greetings, long time lurker, first time poster.

I have a project where the incoming supply, 1000kVA, derated to 1400A via ACB is provided from an adjacent transformer via single core AWA/XLPE cables in a concrete trench, fixed on containment horizontally with ventilated covers.

The sub-contractor has sized the cables in accordance with installation number 117 from table 4A2. As such is proposing to use 300mm2 cables in parallel.

My interpretation is 117 is not applicable as more than 3 cables are to be placed horizontally, and method 118 is applicable, which is subject to derating as per table 4C6.

Some further input would be appreciated.
 08 November 2017 02:02 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 16014
Joined: 13 August 2003

Are the cables fixed/placed on the floor of the trench, or suspended a little above by the containment? If they're in effect 'in free air' rather than 'clipped direct' I could see an argument that perhaps 117 might be a closer approximation than 118.
- Andy.
 09 November 2017 10:25 AM
User is offline View Users Profile Print this message



Stuz

Posts: 5
Joined: 19 May 2016

Fixed to 41x41 unistrut @ 900mm centres, which is fixed direct to the bottom of the concrete trench.

Edited: 09 November 2017 at 11:30 AM by Stuz
 09 November 2017 07:17 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 16014
Joined: 13 August 2003

Wait to see what the 'big boys' say, but I suspect an inch and half gap (presuming the cable doesn't sag significantly between supports) will allow much more cooling that just sat on the trench floor. A single horizontal row of cables probably cools better than a vertical arrangement too (no heat from other cables below).

I've just noticed that the other difference between 117 and 118 is that 117 has a ventilated cover while 118 has a solid one - so in that respect too 117 sounds a bit closer to your setup than 118.

- Andy.
 09 November 2017 07:49 PM
User is offline View Users Profile Print this message



Nedryerson

Posts: 105
Joined: 12 December 2009

Stutz,

Why 'derated' ? 1400A is about right,

Ned
 09 November 2017 07:51 PM
User is offline View Users Profile Print this message



Nedryerson

Posts: 105
Joined: 12 December 2009

Stutz,

How long are the cables ?

Ned
 09 November 2017 08:16 PM
User is offline View Users Profile Print this message



Nedryerson

Posts: 105
Joined: 12 December 2009

Stutz,

To be clear

2 x 300mmsq SC per phase ?
2 x 300mmsq neutral ?

8 cables plus earth ?

Cable diameter 33mm separated by one cable diameter = 17 x 33 = 561mm.

Given the above neither 117 or 118 is applicable. The thing is, are his calculations verifiable ?

Ned
 10 November 2017 03:33 PM
User is offline View Users Profile Print this message



Stuz

Posts: 5
Joined: 19 May 2016

Set to 1400A to specifcation.
Length 15m in ground.
2x 300mm2 per phase 1x N
 10 November 2017 05:16 PM
User is offline View Users Profile Print this message



rocknroll

Posts: 9549
Joined: 03 October 2005

Have you tried 118 118 LOL had to get that one in.

Regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 13 November 2017 02:44 PM
User is offline View Users Profile Print this message



Stuz

Posts: 5
Joined: 19 May 2016

Originally posted by: Nedryerson


Given the above neither 117 or 118 is applicable. The thing is, are his calculations verifiable ?


Which method would be more suited?
Statistics

New here?


See Also:



FuseTalk Standard Edition v3.2 - © 1999-2017 FuseTalk Inc. All rights reserved.

..