It must be in duplicate.

Such duplication may be pro- Sec 44 vided either by not fewer than two separate boilers, engines, and dynamos, each capable of supplying the maxi- mum ordinary load, or, in lieu of one engine and dynamo, a battery of approximately equal capacity for a minimum period of five hours, and such battery shall be fully charged before the commencement of every performance, or another alternative may be adopted by obtaining a full supply from the mains of a public company or borough council by means of proper change-over switches.

The position and the construction of the change-over switches shall be subject to the approval of the Council.

Where gas engines are used, a battery or other duplicate supply shall be provided, gas engines alone shall not be accepted as sufficient.

No un- licensed building or unlicensed portion of a building shall be supplied from any part of the installation of the licensed part of the building unless the installation in such un- licensed portion is open to inspection and testing by the Council.