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Topic Title: 10 mm tails and upgrading/periodic inspection
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Created On: 23 August 2013 01:57 PM
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 23 August 2013 02:19 PM
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peteTLM

Posts: 3212
Joined: 31 March 2005

So the 10mm tails only do the small little unit, and the main cu has 25mm? No issue there.

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

Every man has to know his limitations- Dirty Harry
 23 August 2013 05:31 PM
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UKPN

Posts: 535
Joined: 17 January 2012

you could look at it as in a 185mm main, feeding a busbar, then 95s 120s etc off that.

Regards
 23 August 2013 06:10 PM
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perspicacious

Posts: 7251
Joined: 18 April 2006

" tho there is no safety issue?"

537.1.4 ?

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BOD
 23 August 2013 06:17 PM
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aatomic69

Posts: 20
Joined: 23 August 2013

As to above comment, not sure where 537.1.4 comes into this.
circuit breaker and isolation is at origin of installation.
 23 August 2013 06:51 PM
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perspicacious

Posts: 7251
Joined: 18 April 2006

I read your OP as an existing CU having a main switch with the original 25 mm2 "meter tails" and then someone shoving some 10 mm2 into the incoming "live" side to have 35 mm2 of copper in the incoming so that to isolate the supply, you have to operate TWO switches.

What is the first word of 537.1.4 and is it plural or singular?

Regards

BOD

By the way, welcome
 24 August 2013 07:56 AM
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dg66

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Joined: 11 January 2008

Two installations sharing one origin?

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Dave(not Cockburn)
 24 August 2013 08:59 AM
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normcall

Posts: 8162
Joined: 15 January 2005

I'm waiting for someone to suggest the obvious.
Install a 60/100A DP block. Must be millions out there like that (honest, I never did most of them!)

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Norman
 24 August 2013 01:28 PM
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aatomic69

Posts: 20
Joined: 23 August 2013

yea the supply split via blocks
 24 August 2013 02:01 PM
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antric2

Posts: 1081
Joined: 20 October 2006

Surely, the 10mm is in an issue if they are directly supplied from the main incomer from a main intake fuse of 80A or above so would need upgrading to 16mm minimum tails if thats the case........fuse protecting cable and all that!
25mm is fine
Regards
Antric
 24 August 2013 02:02 PM
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normcall

Posts: 8162
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So the 'maximum' load the 10mm would be about 40A.
Explain the problem again.

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Norman
 24 August 2013 02:11 PM
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antric2

Posts: 1081
Joined: 20 October 2006

Originally posted by: normcall

So the 'maximum' load the 10mm would be about 40A.

Explain the problem again.


Hiya Norman,
I read the OP as a small con unit having 10mm tails supplying it and than it is distributing via a 40A breaker.
I am looking at the 10mm supply, if there was aproblem between incomer and con unit then the tails could become a form of' chinese cracker' because the incomer,if 80A or above may not blow.I know I am being extreme but also most heads are now being upgraded to 100A .
Regards
Antric.
 24 August 2013 02:34 PM
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daveparry1

Posts: 6325
Joined: 04 July 2007

The 10mm tails would handle a short circuit fault ok and as the max. load can only be 40 amps there is no worry as far as an over current fault is concerned. (just as Norm said really!)

Dave.
 25 August 2013 10:39 AM
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aatomic69

Posts: 20
Joined: 23 August 2013

Thx for the input guys, I forgot to mention that we do fuse the service head at 60amp if 10mm tails are found.

Just that we have to fit an isolator and advise the customer of upgrading 10mm tails.

Just don't see the point of customer upgrading the 10mm tails in this scenario(40amp max load).

That's why I ask if theres any regs on min tail sizes to consumer units of this size.

Also all new service heads are fused at 80amps unless authorised by the DNO. (by meter fitter)
 25 August 2013 09:28 PM
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antric2

Posts: 1081
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Originally posted by: daveparry1

The 10mm tails would handle a short circuit fault ok and as the max. load can only be 40 amps there is no worry as far as an over current fault is concerned. (just as Norm said really!)



Dave.


In the real world, I do agree with you Dave,but, from what the OP is asking ,and working to a regulation point of view,10mm tails must be recommended to be upgraded if they are run direct rom a main incoming fuse of 60A or above.
The 40 A MCB is irrelevant with respect to his question but agin,I agree that the load if shorted out would operate the 40A MCB.
Now to play the 'devils regulation advocate' If the 10mm tails are ...say....under a stairs cupboard and every day ...say... an ironing board was taken in and out of the cupboard and gradually chaffed the 10mm tails ....the 40A breaker wontprotect them and a 100A intake fuse may cause the iron board or even the tails themselves to become an involuntary heater element because the chaffed tails arnt damaged enough to cause a dead short so wont draw enough current to take the fuse out. A million million to one chance but it is still there.
Is it a recommendation on an EICR to upgrade....yes it is.
Regards
Antricf
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