Design of transformer manholes and vaults

SECONDARY network systems serving a distributed load, without substantial concentrations of power, generally are supplied from individual transformer installations strategically located for maximum economy in distribution. Such single-transformer installations are commonly located in the roadway where they may be subjected to flooding and hence submersible equipment is used. These manhole units are connected to the network mains and usually have no customer service connection. On the other hand, where substantial concentrations of load occur, say in the order of 200 kva or more, transformer installations adjacent to the customer's service point are indicated. These vault installations provide for a customer's service connection and have a secondary tie to the street network. The number of banks required in a multiple-bank installation will be determined by the customer's maximum demand, the size of transformer used, the design of the secondary network system, and the permissible loading of the transformers under emergency conditions.