Fuse Ratings
My test multimeter has a current range, protected by a 440mA fuse.
The fuse is rated to blow at, typically, 440mA to protect the meter but can cope with 10kA.
If I connect the meter across the mains when set to amps range (STUPID
) there will be a finite time that the meter will carry a high current - way in excess of 44mA - this will be limited by the circuit impedance (mains supply, test leads and meter - guess at 1000 A ?). There will be molten copper where the test lead probe tips were. There will be an audible 'pop'.
When the meter designers chose the fuse (I hope) they will have considered the above and rated the fuse to safely break the circuit. The moten copper from the probe tips could be forming a growing arc now, due to the high temperatures causing the air to ionise.
My meter is now history but I survived to buy a new one :wink: (sounds like I tried it?).
HRC = high rupture capacity - now called ...
HBC = high breaking capacity
Typical breaking capacity = current that will eventually blow the fuse (could take a second or so)
FF = super-quick action (for semiconductor protection)
F = Quick Acting (normal fuses)
M = Medium (slower than normal !!!)
T = Time Lag (Slow-Blow)
TT = Super Time Lag
FF will blow in 1mS with 10 (TEN) times its rated current.
TT will last nearly a second with 10 (TEN) times its rated current.
All this for a thin bit of wire !