What is the maximum rating allowed for the overcurrent protective device for a circuit using 10 AWG XHHW aluminum conductors supplying an electric water heater?

In determining the maximum rating for the overcurrent protective device for a circuit using 10 AWG XHHW aluminum conductors, it is important to consider the National Electrical Code (NEC) and the ampacity of the conductors. For 10 AWG aluminum conductors, the typical ampacity is generally considered to be 30 amps under favorable conditions.

However, there are specific rules in the NEC regarding the application of overcurrent protection for specific types of loads, such as water heaters. The NEC requires that overcurrent protective devices be sized to protect the conductors from being damaged and to ensure a safe operation of the equipment. For most residential water heaters, it is common to use a lower ampacity to account for continuous loads and potential inrush currents.

In this context, the National Electrical Code specifies that for a water heater, the maximum rating of the overcurrent device should not exceed 25 amps when using 10 AWG aluminum conductors. This takes into account the continuous duty nature of water heaters, as they can draw close to their full load current under certain conditions. Therefore, the selected answer of 25 amps aligns with the NEC standards for providing adequate protection while preventing overheating and potential failure of the conductors.

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