Fuses and circuit breakers are designed to interrupt the power
	to a circuit when the current flow exceeds safe levels.  For
	example, if your toaster shorts out, a fuse or breaker should
	"trip", protecting the wiring in the walls from melting.  As
	such, fuses and breakers are primarily intended to protect the
	wiring -- UL or CSA approval supposedly indicates that the
	equipment itself won't cause a fire.

	Fuses contain a narrow strip of metal which is designed to melt
	(safely) when the current exceeds the rated value, thereby
	interrupting the power to the circuit.  Fuses trip relatively
	fast.  Which can sometimes be a problem with motors which have
	large startup current surges.  For motor circuits, you can use
	a "time-delay" fuse (one brand is "fusetron") which will avoid
	tripping on momentary overloads.  A fusetron looks like a
	spring-loaded fuse.  A fuse can only trip once, then it must be
	replaced.

	Breakers are fairly complicated mechanical devices.  They
	usually consist of one spring loaded contact which is latched
	into position against another contact.  When the current flow
	through the device exceeds the rated value, a bimetallic strip
	heats up and bends.  By bending it "trips" the latch, and the
	spring pulls the contacts apart.  Circuit breakers behave
	similarly to fusetrons - that is, they tend to take longer to
	trip at moderate overloads than ordinary fuses.  With high
	overloads, they trip quickly.  Breakers can be reset a finite
	number of times - each time they trip, or are thrown
	when the circuit is in use, some arcing takes place, which
	damages the contacts.  Thus, breakers should not be used in
	place of switches unless they are specially listed for the
	purpose.

	Neither fuses nor breakers "limit" the current per se.  A dead
	short on a circuit can cause hundreds or sometimes even
	thousands of amperes to flow for a short period of time, which
	can often cause severe damage.


User Contributions:
Dev
Dec 21, 2011 @ 12:00 am
In a fire protection circuit, circuts are shown witha no example 6,8,4etc. what it mean?these circuits are connected between smode detector,junction box etc
kevin
Dec 24, 2011 @ 12:12 pm
My daughter dropped a small necklace behind her dresser. The necklace crossed a plug terminal and shorted the receptacle.

I bought a new receptacle and installed the same. I still have no power  I suspect there could be a bigger problem,this is aluminum wiring.

I've killed the breaker and call an electrician but am curious as to what happened.P.s. there is a dimmer switch on the same circuit.
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