Physics Question

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Hi all

I’m doing an assignment for physics class and its to do with electrics. The question is:

Which one of the following would cause an unsafe situation?

a. A 6 amp fuse in a 60 amp circuit
b. A 60 amp fuse in a 6 amp circuit
c. A 60 amp wire fuse in a 80 amp circuit
d. A 6 amp cartridge fuse in a 60 amp wire fuse way

I do not just want the answer but an explanation would be helpful in helping me understand why it is the answer, many thanks.
 
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a. A 6 amp fuse in a 60 amp circuit
The fuse would go pop, it depends what the circuit is running as to wether or not it will cause danger.
b. A 60 amp fuse in a 6 amp circuit
Not a good combination, can cause meltdown and fire.
c. A 60 amp wire fuse in a 80 amp circuit
See a.
d. A 6 amp cartridge fuse in a 60 amp wire fuse way
See a, also how would you fit a cartridge fuse into a rewirable fuse way?
 
So would you go with "b"?

also do u go with bigger or smaller fuses if your circuit is 60 amp, just trying to understand how all this works, sorry for sounding thick.
 
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Yes b.
Never fit a bigger fuse than the circuit is designed for, the fuse is a safety device to protect the circuit.
 
The fuse is there to protect the wiring/circuit etc. It is basically a purposefull weakest link which you want to fail before the circuit gets hot, melts, explodes etc.

Yep, you can get 60A fuse wire, BS7671 even has a graph for it in the appendix.
 
Thanks guys

Now why couldn’t our physics teacher explain it in simple terms like u guys, instead she rather stand in front of the class and read from a “how to teach physic when you have no idea what your talking about” guide book for teachers!
 
Which one of the following would cause an unsafe situation?

a. A 6 amp fuse in a 60 amp circuit
b. A 60 amp fuse in a 6 amp circuit
c. A 60 amp wire fuse in a 80 amp circuit
d. A 6 amp cartridge fuse in a 60 amp wire fuse way
None, until an electrical load is put through the circuits.

As for b, the vastly overrated fuse does not make the circuit unsafe, it's the fault in the circuit that will cause the house to burn down. Which would be a pity, as the correct fuse might have saved it.

These comments are not likely to move you to the top of the class, but you will impress with your wit and analytical skill.
 
As for b, the vastly overrated fuse does not make the circuit unsafe, it's the fault in the circuit that will cause the house to burn down. Which would be a pity, as the correct fuse might have saved it.

These comments are not likely to move you to the top of the class, but you will impress with your wit and analytical skill.
No - they are likely to make him look like a fool.

Of course the vastly overrated fuse makes the circuit unsafe!

A car with no brakes is unsafe to drive whether you drive it or not.

A ladder with broken rungs is unsafe to climb whether you climb it or not.
 
I have to agree with BAS; there doesn't have to be a fault to make (b) unsafe. The question must be "Is it possible that somebody will severely overload this circuit?"

I have a vivid memory of my mother plugging her electric iron into an overhead light socket. :eek: :eek: :eek: It was common practice in the fifties and early sixties when wall sockets, mostly two pin five amp, were few and far between. We had a 750W 'heater' lamp too. Now imagine that circuit with a 60 amp fuse in the box! :!: :!: :!:

That particular scenario is unlikely to happen today but in its place we have room lighting on a scale undreamt of in the fifties when a 100W bulb was big. Today we have massed arrays of halogen spotlights that can outdo a football stadium. And why not, as long as the wiring can take the load. :cool: :cool: :cool:

It's true that nothing nasty will happen unless the circuit is overloaded but that doesn't make it safe. Fuses are there to save the day when somebody DOES overload it. :) :) :) I once knew a lab technician who got fed up with a 3kW electric furnace that kept blowing its plug fuse. His unorthodox 'cure' was to put some brass bar in the plug! :rolleyes: :rolleyes: :rolleyes: Luckily for him - and the building - there was a 30 amp breaker upstream.

PS: The furnace was eventually scrapped and that technician got a job as a lecturer in electronic engineering!
 
As for b, the vastly overrated fuse does not make the circuit unsafe, it's the fault in the circuit that will cause the house to burn down. Which would be a pity, as the correct fuse might have saved it.

These comments are not likely to move you to the top of the class, but you will impress with your wit and analytical skill.
No - they are likely to make him look like a fool.

Of course the vastly overrated fuse makes the circuit unsafe!

A car with no brakes is unsafe to drive whether you drive it or not.

A ladder with broken rungs is unsafe to climb whether you climb it or not.
Perhaps the words you are looking for are "potentially dangerous or unsafe"?
 
No - I'm not.

There is potential for a fire (for example). There is no potential for danger - the danger is real.

People do things which are dangerous, or unsafe, all the time. The fact that they get away with it does not mean that what they did was not dangerous or unsafe, it just means that the potential for <whatever> to happen remained just a potential.
 
The fuse is supposed to be the weakest link in the circuit. All other components, cable, connectors etc are supposed to be rated higher than the fuse, so if a fault occurs, the fuse melts and not the cable.

b is the most dangerous because the wire which may only be rated at 6 Amps will melt before the fuse blows
 

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