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Topic Title: 160A supply, tail & equipotential bonding sizeing
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Created On: 24 February 2010 11:22 PM
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 24 February 2010 11:22 PM
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Smith249

Posts: 362
Joined: 09 September 2004

Guys,

160A 3phase supply, main tails 2m run straight out of CT meter into steel trunking into panel board. Calc 50mm would do 167A, but would 70mm be the better option?

25mm earth to MET?

Main equipotential bonding...can I get away with 16mm?

Thanks

 25 February 2010 02:42 AM
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jleltd

Posts: 199
Joined: 11 March 2009

Originally posted by: Smith249

Guys,



160A 3phase supply, main tails 2m run straight out of CT meter into steel trunking into panel board. Calc 50mm would do 167A, but would 70mm be the better option?



25mm earth to MET?



Main equipotential bonding...can I get away with 16mm?



Thanks


Assuming TN-C-S

50mm tails

25mm Earthing conductor.

16mm Bonding conductors



70mm tails

35mm Earthing conductor

25mm Bonding Conductors


If the Installation is unlikely to draw 160A which I suppose it wont go with the 50mm but if they load is likely to increase with a possibility of a upgrade to 200A go with 70mm.
Always the option of XLPE tails if you have allowed for PVC that will give a bit more current carrying capacity.

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James
 25 February 2010 10:16 AM
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Avatar for OMS.
OMS

Posts: 19693
Joined: 23 March 2004

Always the option of XLPE tails if you have allowed for PVC that will give a bit more current carrying capacity.


But at the risk of equipment terminals potentially exceeding 70C I guess

OMS

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Failure is always an option
 25 February 2010 10:36 AM
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perspicacious

Posts: 7236
Joined: 18 April 2006

"160A 3phase supply, main tails 2m run straight out of CT meter into steel trunking into panel board. Calc 50mm would do 167A, but would 70mm be the better option?"Smith249

I "borrowed" the nice colour A4 sheet from the Metering Services guy last month and the table for 50 mm2 "meter tails" in trunking gives 134 A and that box is pink, so 100 A will be fitted.

For 70 mm2 in trunking the rating is 171 A and that box is green allowing the meter person to fit 160 A fuses.

There are tables for XLPE cable but I've yet to find a manufacturer willing to confirm that their equipment is suitable for use above 70 degrees C.

It depends how far you want to push your ethos of "can I get away with"

Regards

BOD
 25 February 2010 10:42 AM
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perspicacious

Posts: 7236
Joined: 18 April 2006

"If the Installation is unlikely to draw 160A which I suppose it wont go with the 50mm but if they load is likely to increase with a possibility of a upgrade to 200A go with 70mm."jleltd

From the same table, 200 A fusing is "red" so the cable size for "enclosed in trunking" is 95 mm2 as this is listed at 207 A.

For "yellow" 250 A fusing where the cable is in trunking, 150 mm2 listed at 262 A is required.

Regards

BOD
 25 February 2010 06:02 PM
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jleltd

Posts: 199
Joined: 11 March 2009

I feel the trunking ratings for meter tails is a little over the top as the cables generally are never grouped and say 4x70mm cables in a 100x100mm trunking is going to dissapate heat better than the reference method would suggest.

The boards cutout is suitable for XLPE cable as that 160A supply will be either run in 70 or 95mm XLPE multicore aluminum cable so the terminals will have to put up with that.

I would like to see this document from the supplier suggesting tails sizes as it differs from the information we have been given.

The main switch of the panelboard will have to be verified for XLPE though.

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James
 25 February 2010 08:28 PM
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peteTLM

Posts: 3169
Joined: 31 March 2005

Bod, could you possibly scan and distribute aforementioned 'borrowed' document please? For information only of course.

P

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