Which of the following characteristics is not required of grounding electrodes according to Article 250?

Grounding electrodes are essential for ensuring safety in electrical installations by providing a pathway for fault currents and reducing the risk of electric shock. Article 250 of the National Electrical Code (NEC) details the requirements for grounding and bonding systems, including grounding electrodes.

In regards to the characteristic mentioned, grounding electrodes do not have to be plated. This means that while certain materials might be used to enhance corrosion resistance or conductivity, there is no universal requirement under Article 250 that mandates grounding electrodes to be plated in a specific way. Therefore, the absence of a plating requirement allows for greater flexibility in the materials that can be used, provided they meet other required characteristics, such as being adequately bonded together and having appropriate dimensions to ensure effective grounding.

The other options mention necessary characteristics that grounding electrodes must possess. For instance, specific thickness and surface area are important because they relate to the grounding electrode's performance in conducting fault currents efficiently. Additionally, bonding grounding electrodes together is crucial for maintaining a low-resistance path for fault current, which is a key safety feature. Hence, while grading and surface area matter, plating is not a required characteristic for grounding electrodes outlined in Article 250.