Mark I don't know were you or the OP are located so I'll answer as if both of you are in the United States. It may indeed be acceptable in a power station that is operated by a utility under the National Electrical Safety Code (NESC). The NESC is the code that is enforced by the public utility regulatory bodies in most states to govern the installation and operation of electrical generating and distribution systems. It is not however compliant with the National Electric Code (NEC) that is adopted and enforced as law by the vast majority of local or state governments in the United States. The NEC is also incorporated by reference into the vast majority of insurance contracts in the US. The NEC requires that materials be approved by the Authority Having Jurisdiction (AHJ). The AHJ can be the local building official, electrical inspector, or the insurance companies loss prevention department. No responsible AHJ will approve the use of an interlock that is not listed by a national electrical testing laboratory.