An ELCB is an Earth Leakage Circuit Breaker. They protect against shorts or current
leakage to ground/earth, such as someone touching a live wire. They are more
important where high earth resistance exists in
isolated systems like a generator. This is because a single ground stake may
not allow enough fault current to flow to blow the fuse, even with a short.
This would be the situation if someone stuck a fork in a toaster, so that the
mains was connected (shorted) to its metal body. The ground connection, earth
stake and the frames of appliances connected can rise up to the full mains
voltage. They are an older type of protective circuit that senses current
leakage to earth. There is a sense coil in the wire connection to the ground
earth stake. They are more or less superseded by Residual Current Devices
(RCDs), which are current balance circuit breakers
where the current in the active and the neutral lines must be the same. If not
balanced we can surmise some is leaking to other places, like ground.
A fuse is an overload protection. The fuse is very simple. It is a piece of
wire in the line that is smaller than the rest of the wiring, so it blows
(melts) first, before the wiring gets too hot. The wire is chosen so that it
can carry a specified current indefinitely, and opens/blows within a specified
time for a specified overload current. A large fuse shows why the term
"blows" is used. They really do blow with a loud bang and brilliant
flash. There are also overload circuit breakers (a circuit breaker is an
automatic switch) operated by magnetic or thermal means. These are more
precise, and perhaps quicker than fuses when the overload is marginal.
No comments:
Post a Comment