Chapter 19.2, Problem 1R

To determine

State which ungrounded conductors should be disconnected by the high-temperature limit control as per NEC 422.47 and provide the maximum water temperature that is limited by the high-temperature control.

Answer to Problem 1R

The high-temperature limit control should disconnect all the ungrounded conductors and the maximum water temperature limits to $\underset{\_}{190}°\text{F}\left(\underset{\_}{88}°\mathrm{C}\right)$.

Explanation of Solution

Discussion:

According to National Electric code NEC 422.47, the high-temperature limit control must disconnect all the ungrounded conductors.

Electric water heaters, which are utilized in residential, are listed under UL safety Standard 174, “Household Electric Storage Tank Water Heaters”.

The NEC and UL standard suggest that the electric water heater should be equipped with high temperature cut-off for safety purpose. The high-temperature control limits the water temperature into the maximum limit of $190°\text{F}\left(88°\mathrm{C}\right)$.

Conclusion:

Thus, the high-temperature limit control should disconnect all the ungrounded conductors and the maximum water temperature limits to $\underset{\_}{190}°\text{F}\left(\underset{\_}{88}°\mathrm{C}\right)$.