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Topic Title: XLPE/PVC Cable Current Carrying Capacity
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Created On: 02 December 2009 02:24 PM
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 02 December 2009 02:24 PM
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geeli

Posts: 61
Joined: 21 April 2005

Hi all

What is the current capacity of a 4 core 185mmsq 600/1000V XLPE/PVC unarmoured cable housed in upvc pipe laid underground?

I am unable to find it in any cable catalogue as it seems that ONLY
armoured cable can be laid underground.

Can unarmoured cable but housed in upvc pipe laid underground?

Appreciate your valued input.

Thanks.
 02 December 2009 03:25 PM
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Ricicle

Posts: 829
Joined: 23 October 2006

Originally posted by: geeli

Can unarmoured cable but housed in upvc pipe laid underground?



Appreciate your valued input.



Thanks.


No - there is no earthed mechanical protection !

-------------------------
Empty barrels make the most noise.
 04 December 2009 12:06 PM
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geeli

Posts: 61
Joined: 21 April 2005

Originally posted by: Ricicle

Originally posted by: geeli



Can unarmoured cable but housed in upvc pipe laid underground?







Appreciate your valued input.







Thanks.




No - there is no earthed mechanical protection !


But mechanical protection can be effected by housing the cable in upvc pipe and then encased in concrete..
 04 December 2009 01:00 PM
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Ricicle

Posts: 829
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No - the whole idea is for the mechanical protection to be earthed so that it will cause the protective device to operate if someone was unfortunate enough to penetrate the cable.
I would still not like to see unprotected cables in concrete as a digger bucket could still possibly get through to them.

-------------------------
Empty barrels make the most noise.
 04 December 2009 01:43 PM
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OMS

Posts: 18917
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Originally posted by: Ricicle

No - the whole idea is for the mechanical protection to be earthed so that it will cause the protective device to operate if someone was unfortunate enough to penetrate the cable.

I would still not like to see unprotected cables in concrete as a digger bucket could still possibly get through to them.


Doesn't your view tend to cut across installation methods 70 and 71 perhaps.

522.8.10 doesn't demand an earthed metallic sheath - just that protection from mechanical damage is considered. I know several installations that have insulated and sheathed single core conductors in ducts and concrete cableways - some of them exceeding 500mm2

Regards

OMS

-------------------------
Failure is always an option
 04 December 2009 02:07 PM
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spinlondon

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Originally posted by: OMS
Doesn't your view tend to cut across installation methods 70 and 71 perhaps.

Are they new ones?
 04 December 2009 02:15 PM
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OMS

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Originally posted by: spinlondon

Originally posted by: OMS

Doesn't your view tend to cut across installation methods 70 and 71 perhaps.


Are they new ones?


January 1st 2008 I believe Spin

For a bit of nostalgia you could try Installation Method 16 in BS 7671.2001 (AMD 2:2004)


Regards

OMS

-------------------------
Failure is always an option
 04 December 2009 02:28 PM
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spinlondon

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Correction for method 3 or 4 would be my choice.
Must admit, I'm not aware of any regulation precluding the use of non armoured cables buried in ducting in the ground.
I thought it was just buried direct in the ground had to be armoured, or concentric.
 04 December 2009 03:44 PM
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geeli

Posts: 61
Joined: 21 April 2005

thanks for all response.

Indeed there is no clear cut method for unarmoured cable run in duct and further encased in concrete buried in ground.

In fact such method offer more mechanical protection compared to an armoured cable laid directly in ground.

On my part.. i am planning to use 1 x 4C XLPE unarmoured cable + a separate 1C green/yellow (CPC) in duct encased in concrete buried in ground.

The reason is that the cable will, from a switchroom, run in ground for some distance before surface out and running on perforated cable tray into an apartment. Hence using armoured cable seems bulky/weird.

Do keep this topic alive and hopefully we can gather more view and can reach a common ground or perhaps a new method of installation which in my humble opinion is rather widespread.
 04 December 2009 04:19 PM
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OMS

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The reason is that the cable will, from a switchroom, run in ground for some distance before surface out and running on perforated cable tray into an apartment. Hence using armoured cable seems bulky/weird.


Must be some apartment to warrant a cable that size. If you are happy to have surface tray what's so wierd about armoured cable on it.

To be clear, I guess it's a NYY type of cable construction you are aiming for

Regards

OMS

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Failure is always an option
 04 December 2009 08:41 PM
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kermit1202

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Taken from guidance note 1

5.7

Cables to be installed in ducts or pipes in the ground are not required by BS7671 to have armouring and / or a metal sheath, if the duct or pipe is sufficiently strong to resist likely mechanical damage. in case of doubt, a cable fulfilling the requirements of regulation 522.8.10 should be provided.
 04 December 2009 09:58 PM
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betnwah

Posts: 236
Joined: 16 September 2009

Originally posted by: geeli
What is the current capacity of a 4 core 185mmsq 600/1000V XLPE/PVC unarmoured cable housed in upvc pipe laid underground?

Do you know who makes the cable?
 11 December 2009 10:03 AM
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geeli

Posts: 61
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Originally posted by: betnwah

Originally posted by: geeli

What is the current capacity of a 4 core 185mmsq 600/1000V XLPE/PVC unarmoured cable housed in upvc pipe laid underground?


Do you know who makes the cable?


Cable brand is keystone. http://keystone-cable.com/lowVoltageCables_sub12.html

Anyway what make the cable is irrelevant. Rather it is just regrettable that above method of installation could not be found in the Code hence difficult to determine the current carrying capacity for such installation.
 11 December 2009 10:05 AM
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geeli

Posts: 61
Joined: 21 April 2005

Originally posted by: kermit1202

Taken from guidance note 1



5.7



Cables to be installed in ducts or pipes in the ground are not required by BS7671 to have armouring and / or a metal sheath, if the duct or pipe is sufficiently strong to resist likely mechanical damage. in case of doubt, a cable fulfilling the requirements of regulation 522.8.10 should be provided.


Thank for providing the above quote. By what is the cable current capacity for such method of installation. ??
 11 December 2009 10:06 AM
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geeli

Posts: 61
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Originally posted by: OMS

The reason is that the cable will, from a switchroom, run in ground for some distance before surface out and running on perforated cable tray into an apartment. Hence using armoured cable seems bulky/weird.




Must be some apartment to warrant a cable that size. If you are happy to have surface tray what's so wierd about armoured cable on it.



To be clear, I guess it's a NYY type of cable construction you are aiming for



Regards



OMS


What is NYY.?

Appreciate your clarification. Thanks.
 13 December 2009 02:18 PM
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ArthurHall

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A cable in a duct can carry less current than one laid direct. The theory is that the air in the duct is an insulator so heat is not disapated from the cable. I dont know the exact figures nowadays but the rule of thumb is derate by 60% so instead of a 185 you may have to go to 300
 13 December 2009 03:07 PM
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alancapon

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Originally posted by: OMS
522.8.10 doesn't demand an earthed metallic sheath - just that protection from mechanical damage is considered. I know several installations that have insulated and sheathed single core conductors in ducts and concrete cableways - some of them exceeding 500mm2

Interesting, because quoting from the ESQCR2002 regulation 13:

. . . . Underground cables and associated equipment which contain conductors not connected with earth shall be protected . . . .

(a) in respect of joints or terminations of a conductor in a low voltage system, some form of mechanical protection; and

(b) in respect of any other part of any conductor, an electrically continuous metallic screen connected with earth,

so placed as to ensure that, so far as is reasonably practicable, any tool or device likely to be used in the vicinity will make contact with that protection or screen before it can make contact with any conductors not connected with earth.


Regards,

Alan.
 14 December 2009 10:32 AM
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betnwah

Posts: 236
Joined: 16 September 2009

Originally posted by: geeli
Anyway what make the cable is irrelevant.

No it's not, because you can ask the maker what the CCC is, and whether it is suitable for the installation method you propose.
 14 December 2009 10:57 AM
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stateit

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Originally posted by: geeli

What is NYY.?.


It's construction is similar to hi-tuff, and comes in all sizes. Solid core up to 16mm, stranded and sectional stranded above.

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S George
http://www.sg-electrical.com
 17 December 2009 02:34 PM
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geeli

Posts: 61
Joined: 21 April 2005

Originally posted by: ArthurHall

A cable in a duct can carry less current than one laid direct. The theory is that the air in the duct is an insulator so heat is not disapated from the cable. I dont know the exact figures nowadays but the rule of thumb is derate by 60% so instead of a 185 you may have to go to 300


Is there any cable capacity table for such method of installation that i can refer to?
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