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Q54PE
Expert-verifiedA short circuit to the grounded metal case of an appliance occurs as shown in Figure \({\rm{23}}{\rm{.60}}\). The person touching the case is wet and only has a \({\rm{3}}{\rm{.00 k\Omega }}\) resistance to earth/ground.
(a) What is the voltage on the case if \({\rm{5}}{\rm{.00 mA}}\) flows through the person?
(b) What is the current in the short circuit if the resistance of the earth/ground wire is \({\rm{0}}{\rm{.200 \Omega }}\)?
(c) Will this trigger the \({\rm{20}}{\rm{.0 A}}\) circuit breaker supplying the appliance?
(a) The voltage on the case is \(V = 15\;\;{\rm{V}}\), if \({\rm{5}}{\rm{.00 mA}}\) current flows through the person.
(b) The current in the short circuit is \(I = 75\;{\rm{A}}\), if the resistance is \({\rm{0}}{\rm{.200 \Omega }}\).
(c) Yes, the current will trigger the \({\rm{20}}{\rm{.0\;A}}\) circuit breaker.
When we place a closed coil in a continuously changing magnetic field, a current is induced in the coil such that it opposes the change in the magnetic field. This phenomenon is known as electromagnetic induction.
\(\begin{aligned} {I_p} &= 5.00 {\rm{mA}}\\ &= \left( {\frac{{5.00}}{{1000}}} \right)\;{\rm{A}}\\ &= 0.005 {\rm{A}}\end{aligned}\).
(a)
The voltage on the case will be equal to the voltage drop for the person’s body. For the resistance of body \({R_p} = 3.0\;{\rm{k}}\Omega \) and the current through the body \({I_p} = 0.005 {\rm{A}}\)voltage can be calculated as –
\(\begin{aligned} {V_p} &= {I_p}{R_p}\\ &= 0.005\;{\rm{A}} \times 3000\;\Omega \\ &= 15\;{\rm{V}}\end{aligned}\)
Therefore, the value of voltage is found to be \({V_p} = 15\;{\rm{V}}\).
(b)
The current through the grounding can be calculated using the relation –
\(\begin{aligned} {I_g} &= \frac{V}{{{R_g}}}\\ &= \frac{{15\;{\rm{V}}}}{{0.2\;\Omega }}\\ &= 75\;{\rm{A}}\end{aligned}\)
Therefore, the value of current through the grounding is \(I = 75\;{\rm{A}}\).
(c)
As the current rating for the circuit breaker is \(20.0\;{\rm{A}}\), a grounding current of \(75\;{\rm{A}}\) will trigger the circuit breaker.
Therefore, the circuit breaker will be triggered.
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