Fake Fuses.

Could a fake 13 Amp. plug fuse really blow off the top of


Well in the best 'blow the bloody doors off' tradition, lets do some thinking.



1) gut feel not likely if the circuit feeding it is a modern MCB, either C type 16A or B type 32A.


However, if it was plugged into a circuit protected by a BS3036 hot wire fuse, especially one with a bit of metal coat hanger instead of the original fuse wire, then the let -through energy would be that of the company fuse.

Let's see...


If we assume the fake fuse has a similar resistance to a real one and dissipates 1 watt at 13A, then its resistance is 1/13^2 ohms or about 6 milliohms.



So what is the energy that it will dissipate in joules, well that resistance times the I2t value for the upstream fuse/ADS.


I2t for 30A BS3036 perhaps 160 kilojoules per ohm (say 400A for 0,1 seconds), or about 90 joules in our fake fuse.


if the hot wire fuse has been by-passed for show, then we are looking at maybe a 60A BS1361 perhaps

I2t  is then more like 800kjoules per ohm , so more like 500 joules in the fake fuse (and enough to overheat the plastic,  but not fuse the metal on any 2.5mm2 cable supplying it as well)


To  put that into perspective the energy of a bullet leaving the strongest  air rifle that does not need a licence in the UK is a  little under 5 joules. At point blank range you may get that to crack a plug, but more likely take a chip out of it.

A gram of TNT releases about 4000 joules,  400J or 0.1grams of TNT equivalent would destroy a UK plug, I'm less sure about the total destruction of the plug with 90 joules. It may well blow the back off though.

Mike.

Could a fake 13 Amp. plug fuse really blow off the top of


Well in the best 'blow the bloody doors off' tradition, lets do some thinking.



1) gut feel not likely if the circuit feeding it is a modern MCB, either C type 16A or B type 32A.


However, if it was plugged into a circuit protected by a BS3036 hot wire fuse, especially one with a bit of metal coat hanger instead of the original fuse wire, then the let -through energy would be that of the company fuse.

Let's see...


If we assume the fake fuse has a similar resistance to a real one and dissipates 1 watt at 13A, then its resistance is 1/13^2 ohms or about 6 milliohms.



So what is the energy that it will dissipate in joules, well that resistance times the I2t value for the upstream fuse/ADS.


I2t for 30A BS3036 perhaps 160 kilojoules per ohm (say 400A for 0,1 seconds), or about 90 joules in our fake fuse.


if the hot wire fuse has been by-passed for show, then we are looking at maybe a 60A BS1361 perhaps

I2t  is then more like 800kjoules per ohm , so more like 500 joules in the fake fuse (and enough to overheat the plastic,  but not fuse the metal on any 2.5mm2 cable supplying it as well)


To  put that into perspective the energy of a bullet leaving the strongest  air rifle that does not need a licence in the UK is a  little under 5 joules. At point blank range you may get that to crack a plug, but more likely take a chip out of it.

A gram of TNT releases about 4000 joules,  400J or 0.1grams of TNT equivalent would destroy a UK plug, I'm less sure about the total destruction of the plug with 90 joules. It may well blow the back off though.

Mike.