Today’s blog is a bit technical...but I hope to illustrate the topic with a very easy to understand analogy...so stick with me here...
Okay...let’s say that you’re doing some plumbing...and for whatever reason one of the pipes burst...how do you measure the damage that the water is going to do to your new floor?...by how long it takes you to turn off the main shut-off valve or by how much water actually came out of the pipe?
More than likely you’ll decide on the latter...how much water actually came out of the pipe and is now sitting in a puddle on your floor.
The same basic principle works with over-current protective devices (fuses and circuit breakers) when they’re protecting against a short-circuit (meaning that the device will open VERY quickly...just like you going very quickly to shut off the water)...
So here’s the scoop...each circuit protective device has its own unique rating associated with individual type of fuse or circuit breaker AND the associated amperage. This rating is call the "Let-Thru" rating and is measured in I²t or amp² ï¿½ sec. The clearing I²t is the amount of energy that will be "let-thru" the fuse (or circuit breaker) before it clears the fault.
The clearing I²t of a fuse is like the amount of water that will come out of the pipe before the shut-off valve is turned. The smaller and faster the valve...the less water gets on the floor...the smaller and faster the fuse...the less I²t and the less damage to downstream components.
Engineers will generally choose a fuse that limits the I²t to the withstandability of the downstream components making sure that these components are protected in case of a dangerous short circuit..
Now that concept wasn’t too technical...was it?
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