A portable appliance tester (PAT) performs an earth bond continuity test by flowing 25,text A through the earth conductor and measuring voltage. If the voltage drop is 625,text mV , the earth bond resistance is:

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Electronics Engineering QUESTION #11747

Question 1

A portable appliance tester (PAT) performs an earth bond continuity test by flowing $25\,\text{A}$ through the earth conductor and measuring voltage. If the voltage drop is $625\,\text{mV}$, the earth bond resistance is:

$25\,\text{m}\Omega$✔️
$0.25\,\Omega$
$25\,\Omega$
$0.025\,\Omega$

Correct Answer Explanation

$R = \dfrac{V}{I} = \dfrac{0.625\,\text{V}}{25\,\text{A}} = 0.025\,\Omega = \mathbf{25\,\text{m}\Omega}$. IEC 60950 and EN 60335 require earth bond resistance $\leq 0.1\,\Omega$ (100 mΩ) for Class I appliances. A high earth bond resistance indicates a faulty earth connection that will not safely clear a fault current.

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