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Topic Title: Fuse ratings on tails
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Created On: 25 August 2013 10:46 AM
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 25 August 2013 10:46 AM
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aatomic69

Posts: 20
Joined: 23 August 2013

HI
To all you technical guys on the forum.

Why do we rate service head fuses to tail cable size when the max load is under tail rating?

Eg.
80 amp servce head reduced to 60amp even tho we have an additional one way consumer unit with a 40amp mcb with 10mm tails? (the main consumer unit would be 100amp board with 25mm tails)

Cheers
 25 August 2013 02:40 PM
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geoffsd

Posts: 357
Joined: 15 June 2010

Originally posted by: aatomic69
Why do we rate service head fuses to tail cable size when the max load is under tail rating?

We don't.
On new installations it's the other way round but you can't then uprate the fuse without uprating the tails.

Eg.
80 amp servce head reduced to 60amp even tho we have an additional one way consumer unit with a 40amp mcb with 10mm tails? (the main consumer unit would be 100amp board with 25mm tails)

Not sure what you are asking.
Tails are subject to the same requirements and regulations as any other conductors and circuits.
 25 August 2013 05:32 PM
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prophet

Posts: 240
Joined: 09 October 2011

Why have you made three threads that are pretty much asking the same question?
 25 August 2013 09:47 PM
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antric2

Posts: 1068
Joined: 20 October 2006

Originally posted by: prophet

Why have you made three threads that are pretty much asking the same question?


Because some of the answers in the other threads are relating to real life which I quite agree with but the original question was related with the problem from a regulation and compliant point of view which doesnt always reflect the forever working real life situations....common sense I think its called.....so aatomic may be trying to get to grips with which response answers his question....therefore quite a few threads and fair do to him for keeping on trying to get a correct answer.
Regards
Antric
 26 August 2013 01:02 AM
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alancapon

Posts: 5789
Joined: 27 December 2005

Originally posted by: aatomic69
. . . Why do we rate service head fuses to tail cable size when the max load is under tail rating? . . .

You don't. The tails are protected by the DNO's service fuse. The DNO fit either their standard size, or a larger size if the load justifies it. You then size the tails to meet the DNO's requirements for the tails being protected by their fuse.

Regards,

Alan.
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