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Re: relay AC using DC?
Fuses ALWAYS on LIVE wire, ALWAYS as close to SOURCE as possible (we Brits have them in our power plugs regardless of whether there is also one inside the unit being powered)
5A @ 120Vac = 600W
there are two types of fuses
Fast & Time delay
fast means that an initial surge on the fuse might blow the fuse so you have to use a fuse than can cope with initial surge due to the sudden flow of current. These fuses have either an F or NO letter in front of the fuse rating. ie F1A or 1A
Time delay fuses have a retarding mechanism in the form of a coil like winding, perhaps a ball of solder or even a zigzag effect along the conductor. All designed to allow that initial current surge to pass without blowing.
They are usually marked with a T to indicate that the blow slower than FAST fuses.
ie T1A.
I remember many years ago playing with some units in production and trying different types of fuse on the input to a transformer. I found that, in THAT PARTICULAR UNIT, a T1A was the minimum value "slow blow fuse" whilst a F4A was the smallest value "fast blow fuse" that I could use on the same unit and have it running at the point that I threw the mains switch.
Also note that fuses DO NOT blow at rated value .. normally you can expect the fuse to blow at approx one and a half times the rated value. However the fuse is also liable to fail due to aging if the current flowing through it is approximately the rated value. This may happen though after a few weeks or even a few years
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