The classification of areas for electrical installations requires consideration of all aspects of the construction and operation of the equipment involved. For something like a gas compressor skid, this means at least evaluating the mechanical process, gas process, and the electrical implications. If all these aspects are not considered, then those who operate the equipment may find that what they have is not compatible with their needs. This situation is aggravated when there are only limited inspections to ensure continued conformance. The author discusses a specification developed for the wiring on gas compressors and the process by which it was developed. >