black cut out fuses

Question

i have come across black cut out fuses that light up my single pole tester, but only on the label. 
 my 2 pole tester does not light up from label to MET. 
 is this my single pole tester being over sensitive or should i call 105?

mapj1 · Accepted Answer

This means that L and N are well separated - if you like to imagine the field lines between a pair of wires as they pull apart, the further of the electric field lines fly off before returning, and some dont return at all, but head for the plate at the end of the universe, or local earth.... This illustration is from https://cococubed.com/images/energy/circuit_eb_fields.pdf The magnetic fields (orange/brown - where a compass would point if you put it ther) are proportional in strength to the current, while the Electric fields (black, along which a charge would feel a force if placed at that point) are proportional to the voltage. The closer the wires the more intense the electric field between them, and the less there is 'hanging out' as it were. As a very approximate rule of thumb once you get out to a distance of a few times the conductor centre to centre spacing, it has all but died away. But in some cut out designs, the spacing is an inch or two, so the field is very noticeable/ detectable out to a few times that... 
 PS This illustrates a DC. If it is an AC and a high enough frequency, then the fields at any snapshot in time, are all slightly offset in phase along the wire, completing a full cycle of phase shift over a distance of one wavelength. Not a big issue at 50Hz unless you are wiring a continent or across oceans, the wavelength at 50Hz is 6 megametres (6,000 km) (1GHz is 300mm 1MHz is 300m. 1Hz is 300Mm etc). Earth radius at equator is ~ 7Mm. Mike. 
 edited for silly typo..

black cut out fuses

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