per ring, one on each of L and N, and this duplicated for each of the two feeds for the ring. Manufacturer differences Most of the time, the panels and the breakers inserted inside them must be by the same manufacturer. Each manufacturer has one or more "systems", or kinds of breaker panels, that will only accept breakers of that type. In Europe, this is still the case, despite the adoption of a standard DIN rail for mounting and a standard cut-out shape, as the positions of the busbar connections are not standardized. Certain panels use seemingly interchangeable breakers. However, a given manufacturer will specifically mention exactly which devices may be installed in their equipment. These assemblies have been tested and approved for use by a recognized authority. Replacing or adding equipment which "just happens to fit" can result in unexpected or even dangerous conditions. Such installations should not be done without first consulting knowledgeable sources, including manufacturers. Location and designation For reasons of aesthetics and security, domestic circuit breaker panels and consumer units are normally located in out-of-the-way closets, attics, garages, or basements, but sometimes they are also featured as part of the aesthetic elements of a building (as an art installation, for example) or where they can be easily accessible. However, current U.S. building codes prohibit installation of a panel in a bathroom (or similar room), in closets intended for clothing, or where there is insufficient space for an electrician to gain access to the panel. Specific situations, such as an installation outdoors, in a hazardous environment, or in other out-of-the-ordinary locations might require specialized equipment and more stringent installation practices. Distribution boards may be designated for three phase or single phase and normal power or emergency power, or designated by use such as distribution panels for supplying other panels, lighting panels for lights, power panels for equipment and receptacles and special uses. Panels are located throughout the building in electric closets serving a section of the building. Theatre lighting In a theatre, a specialty panel known as a dimmer rack is used to feed stage lighting instruments. A U.S. style dimmer rack has a 208Y/120 volt 3-phase feed. Instead of just circuit breakers, the rack has a solid state electronic dimmer with its own circuit breaker for each stage circuit. This is known as a dimmer-per-circuit arrangement. The dimmers are equally divided across the three incoming phases.