Which method is not effective in reducing the resistance of the earth?

Using a single grounding electrode is not an effective method for reducing the resistance of the earth. This is because grounding resistance is influenced by several factors, including the type of soil, moisture levels, and the physical dimensions of the electrode itself. A single electrode can often create a high resistance path to ground, especially in less conductive soils.

In contrast, installing multiple grounding electrodes can significantly lower resistance by providing more pathways for electrical currents to dissipate into the earth. This increases the contact area with the earth, which is particularly helpful when individual electrodes may not have sufficient contact to maintain a low resistance.

Chemical grounding enhancement involves the use of specific compounds or materials that increase soil conductivity around the grounding electrode. This can dramatically improve grounding effectiveness, especially in challenging soil conditions.

Increasing the grounding depth can also be effective, as deeper installations typically reach more conductive soil layers, which helps to reduce overall resistance.

Therefore, the method of using a single grounding electrode is less effective because it limits the ability to achieve a low resistance path to ground compared to the other methods listed.