Wednesday, February 23, 2011

The Fuse Vs The Breaker


Yes the lowly Fuse is still superior to Circuit Breakers simple in design it melts it self-open when there is an overload or short circuit and that’s the end of the story.
In fact fuses are still required to be used in the National Electrical Code for such items as
Large Motors and other pieces of equipment that have a large short circuit capability
Why you might ask because
Fuses and breakers are rated 3 ways the first is running amps of the circuit the second a fuse is fast acting or timed delayed to allow high draw devices like motors to start up and third and even more important rating is the short circuit amps, this is the amount of amperage
Available when a particular device short circuits. Even a typical simple house circuit when it short circuits, it has been estimated produces enough energy to light 100 houses for a year in the split second the electrical short circuit is produced. This high- energy flash
Is what is responsible for hundreds of deadly accidents each year and many serious and fatal burns? Individuals suffer from what are known as thermal blasts, which sear the skin .These blasts are measured in Calorie units because they are so high in power.

The average residential breaker is 15/20 amps and has a short circuit rating of 10,000
Amps. Were the typical short circuit power you will find is 6000 amps or less. Were you can find Commercial 15/20 amp breakers with ratings up to 45,000 and fuses up to 300,000 short circuit interrupting amps.
If you improperly design an Residential , industrial or commercial circuit and put in the wrong amount of short circuit protection the fuse or circuit breaker will be destroyed, as it cannot handle the high short circuit amperage. Even if the main fuse rating is correct.
I have seen many times were a fuse will blow in a business and the store owner hires some handyman to come out and correct the situation the handy man pulls out the fuse on a very large Air-conditioning unit which is marked for fuses only and he finds a 60 amp fuse no problem he goes down to the local hardware and gets an of the shelf fuse which is usually only rated at 7000 amps when he should have bought a time delayed fuse with 100,000 amp protection often referred to as a type R fuse.
He puts the off the shelf fuse in starts the unit up and wham there’s a violent arc of light and the handyman is severely burned.
Now had the Air conditioning company done its job correctly when they installed the required fuse disconnect they should have installed the extra kit into the case which only allows Class R fuses as they should have known the potential for damage with an under rated fuse but of course they did not and we have an explosion. Another big problem we are seeing in this country with equipment is that many machines etc. now use European motor starters and relays designed to IEC standards, which call for no damage when an overload occurs and require a class J, fuse not an R, which will cause great damage to equipment. Compared to NEMA standards, which allow for limited damage to components and specifically call for Class R fuses. NEMA equipment is built to withstand limited damage, as IEC is not. Still another problem is when people try to bring home a motor or machine like a lathe from a shop and try to run it of residential power.
Many times again the wrong fuse or breaker is used and when the machine malfunctions it can be deadly.
As you can see electrical circuits can be extremely complicated to design and even more frustrating to investigate. This is why it is crucial that any one investigating fires have a complete knowledge of electrical systems before trying to just pass the buck and say faulty wiring caused the problem. Any one can guess faulty electric caused the fire it is another to get into a court and have to prove it. Yes electric is often to blame but it should
Based on solid science not guesses.

1 comment:

  1. I learned so much about fuses from this article. I did not know that a short can cause an energy surge with enough power to light 100 houses for a year! That is incredible to me and makes me want to make sure that the wiring in my house is more secure. I want to check my air conditioning to make sure that the fuses are correctly installed.