why there is a fault occurs, if a phase wire touches ground.. and the fault no

why there is a fault occurs, if a phase wire touches ground..
and the fault not occurs when we connect a bulb between phase
and ground..??

Question Posted / sudeshkmr16

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why there is a fault occurs, if a phase wire touches ground.. and the fault not occurs when we con..

Answer / 7anoter4

Let's say the cable supplying the outlet [phase-neutral-
ground] is 3*14 awg copper and the length up to supply
panel is 300 ft. The conductor resistance is about 1 ohm[at
rated temperature].For 120 V voltage supply at panel if the
phase contact the grounding conductor the current will be
120/2=60 A. A 15A fuse will burn in less than 1 sec.
However, usually the short circuit current is 500-1000A.
If a bulb is connected between phase and ground ,for a 100
w bulb 120 V the resistance will be 120*120/100=144 ohm.
The current will be 120/144=0.83 A.

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