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Topic Title: Main earth and Protective Bonding sizes
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Created On: 06 November 2012 11:42 AM
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 06 November 2012 11:42 AM
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CPC

Posts: 32
Joined: 16 February 2011

Hello all, just looking for clarification am correct.

Ok i have a new supply going into an existing building (200KW) 3 phase PME. The DNO told me the cable size and type would be a 185mm2 wavecon cable.

I have calucated i need a 70mm2 main earth wire and 25mm2 protective bonding conductors.

Am i correct?????

Many thanks to all.
 06 November 2012 12:01 PM
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perspicacious

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"Ok i have a new supply going into an existing building (200KW) 3 phase PME. The DNO told me the cable size and type would be a 185mm2 wavecon cable.
I have calucated i need a 70mm2 main earth wire and 25mm2 protective bonding conductors.
Am i correct?????"


In a word, no.......

Table 54.8 will give you 35 mm2 copper equivalent as the minimum cross-sectional area of the main protective bonding conductor.

Regards

BOD
 06 November 2012 12:17 PM
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OMS

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LoL -

OMS

-------------------------
Failure is always an option
 06 November 2012 12:29 PM
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CPC

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Ok am abit confused LOL "Again"

185mm2 divide by 2 = 92.5mm2

Copper equivalent cross-sectional area of the supply neutral conductor - over 50mm2 up to 95mm2 = 25mm2

BOD/OMS how do you get 35mm2??

Many thanks again.
 06 November 2012 01:14 PM
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Jobbo

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CPC

The 185mm2 3 core has a neutral CSA of 120mm2

Regards

Jobbo
 06 November 2012 01:25 PM
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OMS

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Originally posted by: CPC

Ok am abit confused LOL "Again"

185mm2 divide by 2 = 92.5mm2

Copper equivalent cross-sectional area of the supply neutral conductor - over 50mm2 up to 95mm2 = 25mm2

BOD/OMS how do you get 35mm2??

Many thanks again.


OK - you need to know your cables and you need to read every word relating to table 54.7 and 54.8. You also need to know that copper and aluminium have a conductivity ratio of about 66% - ie aluminium is approx 66% as conductive as copper for similar CSA.

Wavecon generally has aluminium line conductors and a copper wavecon combined neutral and earth. The wavecon has the same conductivity as the aluminium - ie thy are both able to carry the rated curent of a 185mm2 conductor but the copper wavecon only needs to be 66% the CSA of the aluminium conductor and as such is 185 x 0.66 = 122mm2.

Refer to Table 54.8 and you get a 35mm2 bonding conductor as the direct copper equivalent requirement based on the suppliers neutral.

The earthing conductor needs to be at least 35mm2 and also meet 54.7 if you want to avoid using the daiabatic - that gives you a K1/K2 x S/2 of:

76/115 x 185/2 = 61 - so your selected 70mm2 earthing conductor is fine

Any help ?

Regards

OMS

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Failure is always an option
 06 November 2012 01:50 PM
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Delbot321

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Hi Guys

I was going to write a reply, went for lunch, came back and OMS has beat me too it - well done - good reply.

There seems to be a whole load of replys from people who aren't familiar with wavecon cables and preparing formal designs.

Its worth remembering that if you sign the declaration of compliance for the DESIGN section of the installation certificate you should be doing all the above as it may be needed as your defence in these days of litigation.

With a job this size you should be providing the client an O&M manual which should include the calculations of how you achieved the design. This may seem like extra work, but is it really? You had to do the design in the first place why not provide it along with you list of considerations in place when you did the design. If in the future they change the use of the building you will then not be liable for any changes that have not been considered and therefore it is your defence.

I'll got off my soap box now

Once again - good reply
 06 November 2012 02:07 PM
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CPC

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Thanks to all of you for explaining this too me

Am just a young lad learning

Much appreciate, Thanks once again.
 06 November 2012 05:22 PM
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Jobbo

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Waveform cable be it 3 or 4 core, has a neutral/earth concentric conductor (CU) CSA of approximately 115-120mm2 for sizes 185mm2, 240mm2 and 300mm2.
 06 November 2012 06:02 PM
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OMS

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A bit of cable data on wavecon here

regards

OMS

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Failure is always an option
 06 November 2012 06:15 PM
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stateit

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Originally posted by: OMS

... if you want to avoid using the daiabatic ...

Regards

OMS


Is that the equation used by SWALEC, OMS?

-------------------------
S George
http://www.sg-electrical.com
 06 November 2012 06:45 PM
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OMS

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That's the one - I think Dai abatic used to live up the same street as Ianto Zinc Roof - I often used to ask him where he was going when I saw him coming back

Cofio Cayo and greetings from the daffodil army -

OMS

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Failure is always an option
 06 November 2012 06:54 PM
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mawry

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Dai abatic? Hang your head in shame!!!
 06 November 2012 10:16 PM
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MrOther

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I was having a right mare of a day in which I have yet to learn anything new -- then I opened this thread and learned that the red "HV Cable" -- as we all called it is actually called Wavecon and the reasoning for the reduced CSA of copper earthing (reasons I suspected and now validated.)

So at least today, while being totally stressful, was worthwhile. Thanks all.
 07 November 2012 09:01 AM
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perspicacious

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"Dai abatic? Hang your head in shame!!!"

Isn't he a butty of Dai Versity?

Regards

BAD
 07 November 2012 09:06 AM
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OMS

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LoL - the very chap, BOD

"butty" -

OMS

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Failure is always an option
 07 November 2012 01:47 PM
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ArthurHall

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Mr Other
Red cables are usualy HV, wavecon or waveform cables are LV.
Red cables are generaly SWA or CORAL(corugated aluminium sheath) HV cables dont usualy have a neutral.

Wavecon can be 3 or 4 core. The 4 core is a cheaper replacement for PILC. 3 core in a CNE cable.
The neutral wires are laid in a wavey patern so that the jointer can get enough slack in them to access the cores without cutting the neutral.

Hope this helps it a bit clearer
 08 November 2012 11:13 AM
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CPC

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I take it Wavecon/Waveform is the same cable, just a different name like alot of things??
 08 November 2012 12:15 PM
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OMS

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Waveform, waveconal - A method of layering wires to form a neutral conductor used in low voltage polymeric insulated mains cables.

BS 7870-3.40:2001 - LV and MV polymeric insulated cables for use by distribution and generation utilities. Specification for distribution cables of rated voltage 0.6/1 kV. XLPE insulated, copper wire waveform concentric cables with solid aluminium conductors.

Generally wavecon and wave form describe the same cable construction

Regards

OMS

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Failure is always an option
 08 November 2012 01:24 PM
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CPC

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Thanks again OMS
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