Which of the following methods are permitted for making a splice in grounding electrode conductors?

The correct answer is based on the fact that exothermic welding and irreversible compression connections are widely recognized methods for making splices in grounding electrode conductors due to their reliability and durability.

Exothermic welding creates a strong, permanent bond as it involves a chemical reaction that generates heat to melt the metals being joined, resulting in a robust joint that can withstand environmental stresses. Irreversible compression connections also provide a solid electrical connection by mechanically compressing a connector onto the conductors, ensuring that the joint doesn't come apart easily and providing good conductivity.

In contrast, the other methods listed, while they may work in certain applications, do not meet the stringent requirements for grounding that ensure safety and long-term reliability. Twisted wire connections can be prone to oxidation and corrosion, which can weaken the electrical connection over time. Soldering, although it can create a good electrical joint, may not provide the same level of mechanical strength required for grounding systems and can also be vulnerable to heat-related failures. Insulated crimp connectors, while they are useful for other applications, may not meet the specific requirements for grounding electrode conductors due to potential insulation interference with the grounding function.

Thus, exothermic welding and irreversible compression connections stand out as the most