Final answer:
The minimum size equipment-grounding conductor for a branch circuit protected by a 40-ampere overcurrent device supplying a range receptacle rated at 50 amperes is typically 10 AWG copper wire, as per NEC Table 250.122. The equipment-grounding conductor size is based on the rating of the overcurrent protection device.
Step-by-step explanation:
To determine the minimum size equipment-grounding conductor required for a branch circuit protected by an overcurrent device rated at 40 amperes (and supplying a range receptacle rated at 50 amperes), one needs to refer to the National Electrical Code (NEC) tables. The NEC specifies the minimum conductor sizes based on the overcurrent protection device rating and the conditions of use.
It is generally recommended that the equipment-grounding conductor should not be less than the circuit conductors or rating of the device that is extended. For a 40-ampere circuit, we would typically look at Table 250.122 of the NEC to find the appropriate conductor size. The NEC indicates that an equipment-grounding conductor of 10 AWG copper wire should typically be used for a 40-ampere overcurrent device.
When sizing an equipment-grounding conductor, it is also essential to consider factors like the length of the run and the possibility of voltage drop. Although the question refers to a range receptacle rated at 50 amperes, the minimum size equipment-grounding conductor is determined by the overcurrent device's rating, in this case, the 40-ampere breaker.