Originally Posted by
Barry
Agreed, it's what I use.
Also agree.
Apropos the additional series impedance imposed by a 3A fuse, it is easily calculated.
BS1362 cartridge fuses are 1" long, and for a 3A rated fuse contain a copper wire 0.15mm in diameter. The series resistance is thus 0.025 Ω.
At 50Hz, the skin depth in copper is 9.33mm, so since the wire has a radius of 0.075mm, the current density in the wire is uniform over the cross section of the wire. The inductance is thus μ0/8π = 5.10-8 Hm-1, or 1.27nH. At 50Hz the inductive reactance will be 0.4μΩ.
Thus the series impedance at 50Hz is 0.025 + j4.10-7Ω. This to be compared with the typical source impedance of the UK mains supply at the wall socket of 0.25 + j0.23 Ω (IEC 725:1981 assumes 0.4 + j0.25Ω, so the UK mains supply is a little better in this regard).
Of course with current surges the effective frequency will momentarily be much higher, but even at 1000Hz, the series impedance of the fuse will still be small relative to the source impedance.
Therefore the series impedance of a 3A BS1362 fuse is normally less than one tenth of the mains source impedance, and thus should have absolutely no audible consequences; though some might dispute that.