Big Clive Examines ‘Things you should know about fuses.’

Big Clive takes a look at the construction, design, and application of a few different fuse types including ‘automotive’ (blade) fuses, passive fuses, and industrial fuses, among others. It’s a lengthy video (27 minutes!) but captivating, and I won’t spoil the 15kV expulsion fuse design.


This was supposed to be a short video, but that didn’t happen.
In summary:-

A fuse is designed to be the weakest point in a circuit so that it fails first and breaks the circuit protecting other components and cables.

A 1A fuse does not blow at 1A. It will blow quickly at very high fault currents, but take progressively longer to open the circuit as the current is lowered to nearer its rating.

Glass fuses are only rated to break a low fault current.
Ceramic sand filled fuses can break much higher fault current.

Time delay or slow blow fuses (T) can withstand surges.
Quick blow or fast blow fuses (F) will blow faster in a fault.
Semiconductor fuses (FF) are very sensitive and expensive.

The voltage rating of a fuse indicates its ability to work safely up to that voltage. 3A is 3A so a 250V fuse will work fine on 12V.

If a slow blow is replaced with a quick blow fuse it may keep blowing intermittently. It’s not uncommon for less aware people to replace an anti-surge fuse with the quick blow one they had handy. Then when the fuse blows again the person changing it may replace it with another quick blow because that was what was fitted. Assess the type of load and make an informed decision.

Never short out fuses. People who get over-confident in their fuse-shorting repair skills usually learn the hard way when they bypass too many and cables start going on fire or the last one they put in blows up in their hand causing a shock and burn.
Wrapping fuses in tin foil or adding external wire can end badly due to the unconstrained nature of the fault breaking element. If you create/use a fuse that has a higher current handling ability than the thinnest cable in the circuit, then that cable may go on fire along its full length and cause significant damage to its surroundings.

HRC (High Rupturing Capacity) fuses have the fuse wire running through a fine powder that quenches the arc quickly and forms a solid glass-like substance internally in the process.

Industrial multimeters use HRC fuses so they can break the circuit safely if accidentally applied across a high current supply while in current measuring mode, or if another inappropriate range causes failure. I know they’re expensive, but you must replace them with the correct type of fuse to avoid a scenario where the meter literally explodes in your hands causing shock and burns.

Electronic PTC (Positive Temperature Coefficient) fuses are ideal in many low voltage electronic applications. They work by going high resistance when they get hot and will reset when the power is turned off for a while.

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1 Comment

  1. You forgot the best fuse diagram!

    (BTW, it’s a complete joke ^^ Don’t use those!)

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