ChatterBank1 min ago
Blown 13 Amp Fuse
This may seem like a strange question.. at the time a 13 amp fuse blows what current is actually flowing?
Answers
For domestic electrical systems, Sammo....... ...... what you're referring to is the PFC (Prospective Fault Current) Using Ohm's Law........ R = E/I Therefore I (in this case the PFC) = E/R R, in this case is the value of the EXTERNAL resistance between you and the Power Station or Transformer .......... called Ze Ze will depend on your system...... .. TNCS...
17:52 Thu 02nd May 2013
Any value over 13 amps. It's not that at 12.9999 amps the fuse is fine, and at 13 .00001 amps the fuse will break immediately. There's a transition period where the fuse will start to blow, but will take some time to do so.
For 13 A fuses the guidelines are, according to wikipedia, that the fuse should last for :
1–400 s at 30 A,
0.1–20 s at 50 A
0.01–0.2 s at 100 A.
For 13 A fuses the guidelines are, according to wikipedia, that the fuse should last for :
1–400 s at 30 A,
0.1–20 s at 50 A
0.01–0.2 s at 100 A.
Not exactly in practice -- there is a range associated with the material of which the fuse is made, the characteristics of the current flowing through it, and so on.
Basically a 13 amp fuse has guaranteed tolerance up to about 13 amps, and then a level of tolerance up to maybe 15 or 16, and will start to break for currents somewhere above that value -- the time taken depending on the design and the particular value of current.
Basically a 13 amp fuse has guaranteed tolerance up to about 13 amps, and then a level of tolerance up to maybe 15 or 16, and will start to break for currents somewhere above that value -- the time taken depending on the design and the particular value of current.
For domestic electrical systems, Sammo............. what you're referring to is the PFC (Prospective Fault Current)
Using Ohm's Law........ R = E/I
Therefore I (in this case the PFC) = E/R
R, in this case is the value of the EXTERNAL resistance between you and the Power Station or Transformer .......... called Ze
Ze will depend on your system........
TNCS system 0.35 ohms PFC = 657 amps
TNS system 0.8 ohms PFC = 287 amps
I (PFC) = 230/Ze
In practice, Ze can be much lower. I have a sub-station at the end of my garden, so my Ze is actually 0.1 ohms giving me a PFC of 2300 Amps.
In effect, PFCs are around 600 - 800 Amps. It'll vary around the country of course, but power supplies are unlikely to have the capacity to give a PFC of much more than that.
Using Ohm's Law........ R = E/I
Therefore I (in this case the PFC) = E/R
R, in this case is the value of the EXTERNAL resistance between you and the Power Station or Transformer .......... called Ze
Ze will depend on your system........
TNCS system 0.35 ohms PFC = 657 amps
TNS system 0.8 ohms PFC = 287 amps
I (PFC) = 230/Ze
In practice, Ze can be much lower. I have a sub-station at the end of my garden, so my Ze is actually 0.1 ohms giving me a PFC of 2300 Amps.
In effect, PFCs are around 600 - 800 Amps. It'll vary around the country of course, but power supplies are unlikely to have the capacity to give a PFC of much more than that.
As Jim.....95a..0.1sec
76a...0.2sec
65a...0.4sec
55a...1sec
If the impedance of the circuit is 0.1ohm between phase and earth on a TNCS system then the fault current will be around the 2300 mark resulting in a fuse fail disconnection time of a few micro seconds on a circuit of negligible impedence.The actual fail current of a healthy new fillament would be around 25 a.
76a...0.2sec
65a...0.4sec
55a...1sec
If the impedance of the circuit is 0.1ohm between phase and earth on a TNCS system then the fault current will be around the 2300 mark resulting in a fuse fail disconnection time of a few micro seconds on a circuit of negligible impedence.The actual fail current of a healthy new fillament would be around 25 a.
-- answer removed --