What must be true about every electrical connection or splice?

Every electrical connection or splice must be made in a box to ensure safety and compliance with electrical codes. This requirement serves several important purposes. First, making a connection within a box provides physical protection for the wires and connections from damage, reducing the risk of shorts or failures due to exposure to environmental factors. Second, boxes allow for easy access for future maintenance or inspections, which is critical in residential and commercial settings. Additionally, boxes help contain any potential sparks or heat generated by faulty connections, which enhances overall safety by preventing ignition of surrounding materials.

The other options present misunderstandings about electrical installation standards. Visibility outside the box could pose a safety hazard, and making connections anywhere in the wall could lead to code violations and unsafe conditions. Using any type of fastener might not ensure the stability and integrity required for safe electrical connections, as specific types of connectors and fasteners are designed to meet performance standards.