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blackrose

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On 10/01/2022 at 19:26, Tacet said:

 

Apologies if I was unclear.  That's about it.  It doesn't really contribute much by saying you can run a 150amp gadget via a nominal 5amp plug when there is a transformer involved.

 

I don't know how much a welder draws via the mains but my 140amp welder has yet to break its 13amp (nominal) fuse

 

Standard fuses take a long time to blow even at well above rated current:

 

https://www.pat-testing-training.net/articles/fuse-operation-characteristics.php

 

The grey shaded area shows the minimum and maximum currents at which the fuse will blow -- so for 10 seconds a 13A fuse will carry at least 25A without blowing, and is guaranteed to blow at less than 55A. It will carry 21A forever.

 

Relying on fuses to limit operating current (as opposed to fault currents) is a *bad* idea...

Edited by IanD
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1 hour ago, IanD said:

 

Standard fuses take a long time to blow even at well above rated current:

 

https://www.pat-testing-training.net/articles/fuse-operation-characteristics.php

 

The grey shaded area shows the minimum and maximum currents at which the fuse will blow -- so for 10 seconds a 13A fuse will carry at least 25A without blowing, and is guaranteed to blow at less than 55A. It will carry 21A forever.

 

Relying on fuses to limit operating current (as opposed to fault currents) is a *bad* idea...

 

Indeed, and miniature circuit breakers perform even worse than fuses.

 

As a rough rule of thumb, encapsulated fuses take over twice their rated current to blow reasonably quickly and miniature circuit breakers 3-5 times their rated current.

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I have used 2amp round pin plugs on the boat for decades, with no adverse effect, admittedly most of the appliances have been low consumption items, the only higher consumption unit being a 12v fridge which was hard wired into it's own dedicated circuit.

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On 12/01/2022 at 12:41, IanD said:

 

Standard fuses take a long time to blow even at well above rated current:

 

https://www.pat-testing-training.net/articles/fuse-operation-characteristics.php

 

The grey shaded area shows the minimum and maximum currents at which the fuse will blow -- so for 10 seconds a 13A fuse will carry at least 25A without blowing, and is guaranteed to blow at less than 55A. It will carry 21A forever.

 

Should not the 13a fuse shown blow (at the 10 second scale) on more, not less, than 55a?

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2 hours ago, Tacet said:

Should not the 13a fuse shown blow (at the 10 second scale) on more, not less, than 55a?

No. The current at which the fuse blows after 10 seconds is between 25A and 55A, varying from one fuse to another. Below 25A, no fuse will blow within 10s. Above 55A, all fuses will blow within 10s. In between 25A and 55A the fuse might or might not blow within 10s.

Edited by IanD
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On 12/01/2022 at 12:41, IanD said:

 

 

... 10 seconds a 13A fuse will carry at least 25A without blowing, and is guaranteed to blow at less than 55A. It will carry 21A forever.

 

 

 

13 hours ago, Tacet said:

Should not the 13a fuse shown blow (at the 10 second scale) on more, not less, than 55a?

 

10 hours ago, IanD said:

No. The current at which the fuse blows after 10 seconds is between 25A and 55A, varying from one fuse to another. Below 25A, no fuse will blow within 10s. Above 55A, all fuses will blow within 10s. In between 25A and 55A the fuse might or might not blow within 10s.

 You say No - but seem to mean Yes.  You are saying that a fuse is both certain to blow at less than 55A and yet may not blow at all between 25A and 55A - all in the 10s timeframe.  Between 25A and 55A is definitely less than 55A, of that I am sure

 

In the graph provided, it is only more than 55A at which the fuse is certain to blow within 10s.

 

 

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5 minutes ago, Tacet said:

 

 

 You say No - but seem to mean Yes.  You are saying that a fuse is both certain to blow at less than 55A and yet may not blow at all between 25A and 55A - all in the 10s timeframe.  Between 25A and 55A is definitely less than 55A, of that I am sure

 

In the graph provided, it is only more than 55A at which the fuse is certain to blow within 10s.

 

 

I think we're arguing about different interpretations of what was written, not disagreeing on the facts... 😉

 

You said:

 

"Should not the 13a fuse shown blow (at the 10 second scale) on more, not less, than 55A?"

 

Yes it will definitely blow within 10s above 55A -- but it might also blow above 25A.

 

It will definitely not blow within 10s below 25A -- but it might also not blow below 55A.

 

25A to 55A is a region of uncertainly, where we don't know if it will blow within 10s or not.

 

Agreed?

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Originally designed and rated for single phase 240V A.C. however commonly used on boats for 12v (or 24V if appropriate). Beware there are some who advocate using the neutral and earth pins for the conductors rather than live and neutral on the grounds that you must create a 12V "appliance" with a 240V compatible plug to make use of the socket and if someone unknowingly plugged that "appliance" in to a 240V socket it shouldn't go pop. Personally I'd ensure clear labelling on both plugs and sockets. 

 

5A and 2A AC ratings are common, mostly unfused, they are an old UK standard and quite solidly built (or at least old ones are).  

 

springy

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I  have met the 2A and 5A ones  on hire boats used for the 12V supply for things like the TV.  

 

On land, the 5A ones are often found  used in hotel rooms for mains-voltage standard lamps  which are controlled via wall switches.  

Edited by Ronaldo47
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I have a set of four 2amp sockets in the loft on a fused spur from the lighting circuit, this feeds three security lights and the loft light. It was originally  13amp sockets without the fused spur (done by the previous owner) so I changed it to meet current regs.

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14 minutes ago, blackrose said:

 

Blimey, and I thought I was a hoarder! 😂

There was a time at Berko when I had two lockups, reduced that to one which filled the workshop mezzanine and a shed when I moved to Ringstead. Back to the equivalent of one lock up now hopefully by the end of February I will have got rid of much of it. I still have a full set of Whitworth/BSF spanners and I haven't owned a boat with an engine that needs them for 20years but you never know when I might need them😉

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