Input or Output Wattage

[ban-all-sheds]

My point is this: if you say it's something other than 'it's to protect the wire' I can't see why a 13 Amp fuse wouldn't suffice in every case?

So if I said "it's to protect the internals of the appliance" you'd say that a 13A fuse would always be OK for that?

How bizarre.

 

[ban-all-sheds]

The insulation on flexible cable rated at 3 amps safe carrying current started to melt when the flex was tested at 9 amps. ( Quality assurance testing of materials for a new product )

That's an overload situation, not a fault.

With a 13 amp fuse, depending on its current / time rating, a short in the flex could have as much a 6 Kw of power "liberated" at the short circuit ( fuse carries 26 amps for a short while before melting ).

For how long?

Never mind power - what's the let-through energy of the fuse?

Have you done the calculations to show that the energy would be sufficient to set fire to the cable?

 

[JohnW2]

The insulation on flexible cable rated at 3 amps safe carrying current started to melt when the flex was tested at 9 amps. ...

That's an overload situation, not a fault.

We've been through this one several times. Since BS7671 seems only to consider 'bolted faults' ('dead shorts') you are right in terms of BS7671-speak. However, what I have suggested (and I think Bernard agrees) is that there could be situations in which an appliance normally drawing <3A could draw 9A (or whatever) under certain 'fault' (in everyday sense) conditions, rather than a 'bolted short' current. Whether one calls that a 'fault situation' or an 'overload' one is a matter of semantics and definitions - but the important thing is that, if it happens, it can result in much increased currents, but currents far less than would be seen in a BS7671 'fault' situation.

You, and others, may argue that what I'm describing is very unlikely to occur - and you might be right. However, unless you can think of some problem of using a 1A or 3A fuse when such is adequate for the load, is not a 'just in case' (even if of something very unlikely) approach reasonable and prudent?

Kind Regards, John.