What is required for all electric equipment taken into or used inby the last open crosscut?

For all electric equipment taken into or used inby the last open crosscut, it is essential that the equipment is classified as permissible. This classification means that the equipment is designed and constructed with safety features that minimize the risk of ignition in potentially explosive atmospheres, which are common in mining environments due to the presence of flammable gases or dust.

Permissible equipment is built to stringent standards and undergoes rigorous testing to ensure that it can operate safely under the specific hazardous conditions found in mines. This requirement is crucial in maintaining the safety of miners and preventing catastrophic incidents related to electrical equipment failures.

The other options present different safety measures but do not meet the specific regulatory requirement for equipment used in such hazardous areas. Testing annually or ensuring explosion-proof characteristics, while important in certain contexts, are not the primary classifications required for equipment inby the last open crosscut according to mining safety regulations. Operating equipment solely by a certified electrician also reflects a best practice for maintaining safety, but it does not address the fundamental requirement that the equipment itself must be permissible to protect against ignition hazards.