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Topic Title: 100a SP&N switchfuse + 100a cut-out fuse
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Created On: 07 November 2017 04:29 PM
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 07 November 2017 04:29 PM
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yobby1

Posts: 5
Joined: 30 October 2017

Hi guys

Has anyone ever installed a 100a switch fuse for a sub-main ? Since the cut-out fuse is also 100a, I am wondering whether under fault conditions the cut-out may blow before the sub-main switch fuse ? The sub-main supply is for a workshop.
 07 November 2017 04:36 PM
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WiredScience

Posts: 321
Joined: 25 January 2012

There's no discrimination, but it doesn't matter.

http://www.theiet.org/forums/f...tid=205&threadid=50879
 08 November 2017 11:07 AM
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daveparry1

Posts: 7745
Joined: 04 July 2007

Subject to load required i'd fit a 60/80 amp fuse in there.
 08 November 2017 10:01 PM
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MHRestorations

Posts: 40
Joined: 22 October 2017

Fitted one the other week (Existing CU needed to stay in place but due to an extension the overhead TN-C-S feed needed to be moved).

My view on the discrimination is 'if a fault of that level happens, i'd rather either of them blew' . IF there were 2 submains fed from the same place (think henley blocks with 2 switchfuses) then I'd be more concerned to downrate the fuses on the customer side.
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