IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Cable Cleats or Ties
Topic Summary:
Created On: 08 January 2015 02:23 AM
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 January 2015 02:23 AM
User is offline View Users Profile Print this message



keithmachell1705

Posts: 62
Joined: 05 April 2004

Greetings. I have a scenario and would greatly liek to read your opinions on it. Many Thanks.

I was recently asked my opinion on the fixing of cables using cable ties within trunking for a three phase 800A power supply served by 4no. 300mm single core CU circuits in parallel. The trunking will also serve 6no other power supplies using the same methods.

My view was these should be installed trefoil with cleats. Cleats should then be secured through trunking onto the unistrut support bars beneath at intermittent locations.

I was informed that they would be installed either with cable ties in trefoil, or side by side with neutrals stacked on top.

My experience of short circuit currents (expected to be 30kA) is that this is totally unsuitable and the cables have the potential to cause some serious damage under fault if they're not properly secured.

The trunking is installed on droppers within a ceiling void.

Please advise and provide your pearls of wisdom, experience, thoughts and general comment. Cheques will be issued in the post.

Much appreciated.
 08 January 2015 08:39 AM
User is offline View Users Profile Print this message



timothyarnold

Posts: 215
Joined: 12 January 2012

I had visions of plastic mini trunking being used!

How come you are using trunking rather than cable ladder? The reason i ask is that you will seriously derate your cables. To give you an idea 4x300mm in parallel per phase should be gopd for around 1400A on ladder in free air (usuals apply such as distance, other circuits etc)

In terms of installation there is a guidance note on parallel configurations. I will dig out which GN it is. Essentially it can be trefoil or flat touching - each with its own merits.

I would however be concerned with the heat as above!

How are you terminating each end?

Tim
 08 January 2015 07:28 PM
User is offline View Users Profile Print this message



peteTLM

Posts: 3715
Joined: 31 March 2005

A college lecturer i know, ex eastern electricity, was called out once to a problem with a substation on a private (then MOD) site. The in house maintenance guys had dropped a very large spanner across some lugs in the switch room by accident. Having no protection on the sub LV side, the TX- switchroom cables had tried to re-inact phase rotation until the HV side tripped out.
The cleats and associated metalwork was ripped out of the brick wall which was partly demolished in the process as things went wrong.

Id think twice about the cable ties.......

-------------------------
----------------------------------------
Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 11 February 2015 07:15 AM
User is offline View Users Profile Print this message



keithmachell1705

Posts: 62
Joined: 05 April 2004

Originally posted by: timothyarnold

I had visions of plastic mini trunking being used!



How come you are using trunking rather than cable ladder? The reason i ask is that you will seriously derate your cables. To give you an idea 4x300mm in parallel per phase should be gopd for around 1400A on ladder in free air (usuals apply such as distance, other circuits etc)



In terms of installation there is a guidance note on parallel configurations. I will dig out which GN it is. Essentially it can be trefoil or flat touching - each with its own merits.



I would however be concerned with the heat as above!



How are you terminating each end?



Tim


For the record, I'm not the designer on this one and share your thoughts.

The trunking is galvanized steel and was adopted because of its installation within a return air plenum. Furthermore, the trunking has been referred to as "un-perforated lidded cable tray". This exasperates my concerns and makes it sound like a blatant calculation fudge. I raised my concerns on everything with the designer, but the designer is adamant this is the way he wants to do it. I do not agree, and have acted within my limits and professional code of conduct. I simply said, "I do not agree with this approach Becasue of x, y and z, but if your calculations work based on trunking then there's no issue with me - it will just mean your cables need to be massively oversized to cater for heat dissipation." There's not much more I could do.

The real issue I'm having is the use of cable ties to secure these cables. I will not install based on cable ties despite instruction that I must. I am resisting and opting for cleats, but this is being thrown back at me.

If the calcs are correct the cable sizes in trunking are ok, but the use of clips will still not be sufficient.
 11 February 2015 08:41 AM
User is offline View Users Profile Print this message



mapj1

Posts: 9692
Joined: 22 July 2004

You are correct of course to doubt the wisdom of ties, but apart from flagging it to the Design Authority it sounds like you are stuck with it. The consolation is that so long as you have expressed your concerns, and been over-ruled, then its the DAs insurance that will take a hit should the lights go out as it were (so print out those emails and put them in the back of the folder or whatever...). Of course, its not that likely to happen in the duration of any warranty, but I'd share your feelings of unease - it sounds like something of a a bodge job.

-------------------------
regards Mike
Statistics

New here?


See Also:



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

..