Fusing of Plugtops (UK)

Hi,

The UK mains lead has a fuse in the plugtop that is used to plug into the wall socket. Typically, these fuses are rated at either 13A, 10A, 5A or 3A. The lead may be hard-wired into the unit that it is providing power to - which may, or may not, have an additional protective device fitted internally.

Now, I have just bought a 40W glue gun, wired to a 2A flex connected to a plugtop fitted with a 13A fuse (Mains voltage is 240V)

My question is, what is the likely failure scenario?

A short circuit in the gun or 1m of cable would cause the

13A fuse to blow. Others have used this as an argument that it doesn't matter whether a 3A or 13A fuse is fitted. Does it matter? Why?

If the heater element in the gun could have a failure mode whereby it partially short-circuited, the gun could dissipate 750W, without a 3A fuse blowing. This could easily start a fire. If the partial short-circuit was even more severe, a 13A fuse would not only allow the unit to get very hot - but the cable would be a fire hazard too. However, is a partial short-circuit a viable scenario?

There is another issue in the case of this particular glue gun, in that it has no standards marks of any kind on it. But I did wonder if I could also raise with trading standards the rating of the fuse.

Reply to
Palindr☻me
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Reply to
crugera

This product if new will be suitable for use anywhere in the EU. This means the flex must safely clear a fault where the circuit is protected at 16A as done in some other parts of Europe. The effect of this requirement is to limit the length of lower current rated flex so the resistance of the flex allows rapid clearing of the fault by the fault protection device before the flex has time to become unsafe. So for an appliance which meets current EU standards, you should in theory be able to use a 13A fuse in the plug -- in much of the rest of the EU it will be protected at 16A anyway.

Having said that, I still try and fit the correct rated fuse for the appliance load. There seems little point in not doing so, and it might afford better protection in some cases.

The UK plugtop fuse is only for protecting the appliance flex. If the appliance requires overcurrent (or any other) type of protection for safe operation, the appliance must include such protection in itself. It's not allowed to rely on the plugtop fuse for the appliance safety.

Faults in appliances which generate overcurrent conditions (drawing more current that designed for) rather than fault current conditions (short circuit fault) are rather rare in practice. In your scenario above, the element would probably open circuit in a few seconds quite harmlessly. To draw 750W, the circuit would need to include only around

5% of the 40W element. That 5% would be designed to give off around 2W, and is likely to break rather rapidly if it suddenly starts trying to dissipate 750W, 300 times its designed power dissipation.

It should have a CE mark on it, which means the manufacturer or importer certifies it complies to the relevant EU standards. If the CE mark is missing or applied without ensuring the product meets the EU standards, the manufacturer or importer goes to jail. If you have concerns, contact trading standards who enforce this in the UK.

Reply to
Andrew Gabriel

That makes a great deal of sense.

Thanks, Sue

Reply to
Palindr☻me

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