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Fused spur to Sunamp melted! Why?


oranjeboom

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What turned out not to be the smell of dog's piss in the hallway, but instead a  slowly melting FCU! I have 2 electrical sunamp units ( one is dormant as only 1 bathroom is in action and they are only used for DHW) but the other one will hit charge mode every day  (usually each time after someone's had a shower). So I noticed that the area around the fuse was getting bloody hot, so hot that i have to get my thermal thermometer which read over 110 C! Each time the Sunamp unit would call for heat the smell from the FCU would get worse and towards the end it would start smoking. Not sufficient smoke to set off the smoke alarm, but a real concern that the actual fuse didn't just go pop. 

 

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It's a 13A fuse in there. This is now the 2nd fused outlet that I have had from Toolstation's 'Axiom' range that has seriously overheated but never to this extent. I've got a spare Axiom FCU but a bit hesitant to put that in if it can't cope with the load. Or is there another explanation for the meltdown? The Sunamp's been in use for just over a year with no glitch.

 

The MCB in the CPU is 20A.  The Sunamp units and wiring were all completed by a SA-approved installer. 

 

Any ideas?

 

 

 

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If there was a loose electrical connection the combination of high current and high resistance in the loose ccontact could cause overheating.  On some cheap plates the fuse holder isn't very springy so doesn't press on the fuse very hard.

 

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For these sorts of permanently on big loads, they are best fed from their own radial circuit with a 16A mcb in the consumer unit, and then you don't need an FCU but a 20A double pole switch instead.

 

As others have said this is common with some makes of FCU.

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Each Sunamp has it's own radial with 20A MCB on the fuse board.

 

I'll replace the FCU's with 20A DP switches then and see how that goes. I've switched on the dormant Sunamp unit in the meantime so that we have DHW today at least - bloody expensive backup for a £4 FCU failure!! ?

 

Thanks for the comments!

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