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Electrical Applications 2 by David W. Tyler

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8 Fuse protection
Aims:
At the end of this chapter you should be able to:
Explain the action of circuit protection using fuses.
Describe the construction of common types of fuse.
Define fusing factor.
Explain how afuse limits the energy input to a circuit.
Define arcing andpre-arcing time and sketch a typical current-time
graph for
a
fuse.
FAULT LEVEL
When considering circuit protection, the fault level at the point to be
protected must be taken into account. The fault level is the number
of volt-amperes which would flow into a short circuit if one
occurred at the particular point. On a 415 V three-phase street main
this could be around 2000 kVA, which represents a current of nearly
3000 A. The fault level